EXCHANGE-COUPLED FILM, MAGNETORESISTIVE ELEMENT INCLUDING THE SAME, AND MAGNETIC SENSING DEVICE

Abstract

An exchange-coupled film includes an antiferromagnetic layer, pinned magnetic layer, and free magnetic layer which are stacked. The antiferromagnetic layer is composed of a Pt—Cr sublayer and an X—Mn sublayer (where X is Pt or Ir). The X—Mn sublayer is in contact with the pinned magnetic layer.

Description

CLAIM OF PRIORITY

This application is a Continuation of International Application No. PCT/JP2017/009172 filed on Mar. 8, 2017, which claims benefit of Japanese Patent Application No. 2016-157441 filed on Aug. 10, 2016. The entire contents of each application noted above are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exchange-coupled film, a magnetoresistive element including the same, and a magnetic sensing device.

2. Description of the Related Art

Exchange-coupled films including an antiferromagnetic layer and a pinned magnetic layer are used as magnetoresistive elements or magnetic sensing devices. Japanese Unexamined Patent Application Publication No. 2000-215431 (hereinafter referred to as the patent document) describes that in a magnetic recording medium, an exchange-coupled film can be configured by combining a Co alloy serving as a ferromagnetic film with various alloys serving as antiferromagnetic films. As antiferromagnetic films, alloys such as Co—Mn, Ni—Mn, Pt—Mn, and Pt—Cr are exemplified.

A magnetic sensing device requires solder reflowing (melting) when a magnetoresistive element is mounted on a board. The magnetic sensing device is used in a high-temperature environment such as the vicinity of an engine in some cases. Therefore, an exchange-coupled film for use in the magnetic sensing device preferably exhibits such a high magnetic field (Hex) that the magnetization direction of a pinned magnetic layer is reversed and also exhibits high stability under high-temperature conditions for the purpose of enabling a magnetic field to be detected in a wide dynamic range.

The patent document relates to an exchange-coupled film used as a magnetic recording medium and therefore does not describe the stability of a magnetic sensing device including an exchange-coupled film under high-temperature conditions. Although the patent document exemplifies Pt—Cr as an antiferromagnetic film, the patent document does not describe that composing Pt—Cr at what composition ratio is preferable.

SUMMARY OF THE INVENTION

The present invention provides an exchange-coupled film which exhibits such a high magnetic field (Hex) that the magnetization direction of a pinned magnetic layer is reversed and which exhibits high stability under high-temperature conditions, a magnetoresistive element including the same, and a magnetic sensing device.

An exchange-coupled film according to the present invention includes an antiferromagnetic layer and pinned magnetic layer which are stacked. The antiferromagnetic layer is composed of a Pt—Cr sublayer and X—Mn sublayer (where, X is Pt or Ir). The X—Mn sublayer is in contact with the pinned magnetic layer.

The pinned magnetic layer may be a self-pinned layer including a first magnetic sublayer, intermediate sublayer, and second magnetic sublayer which are stacked.

The thickness of the Pt—Cr sublayer is preferably greater than the thickness of the X—Mn sublayer.

The ratio of the thickness of the Pt—Cr sublayer to the thickness of the X—Mn sublayer is preferably 5:1 to 100:1.

The Pt—Cr sublayer preferably has a composition represented by the formula Pt_XCr_{100 at %-X} (X is 45 at % to 62 at %) and more preferably a composition represented by the formula Pt_XCr_{100 at %-x} (X is 50 at % to 57 at %).

The exchange-coupled film preferably includes a base layer next to the antiferromagnetic layer. The base layer is preferably made of Ni—Fe—Cr.

A magnetoresistive element according to the present invention includes the exchange-coupled film according to the present invention and a free magnetic layer, the exchange-coupled film and the free magnetic layer being stacked.

A magnetic sensing device according to the present invention includes the magnetoresistive element according to the present invention.

The magnetic sensing device according the present invention includes a plurality of magnetoresistive elements, placed on a single substrate, identical to the magnetoresistive element according to the present invention. The magnetoresistive elements include those having different pinned magnetization directions.

A method for manufacturing an exchange-coupled film according to the present invention includes forming a Pt—Cr sublayer by a process for co-sputtering Pt and Cr.

An exchange-coupled film according to the present invention includes an antiferromagnetic layer composed of a Pt—Cr sublayer and an X—Mn sublayer (where X is Pt or Ir) and therefore exhibits such a high magnetic field (Hex) that the magnetization direction of a pinned magnetic layer is reversed is high and increased stability under high-temperature conditions. Thus, using the exchange-coupled film according to the present invention enables a magnetic sensing device which is stable even if the magnetic sensing device is reflowed at high temperature or is used in a high-temperature environment to be obtained.

In accordance with a manufacturing method according to the present invention, an exchange-coupled film including a pinned magnetic layer with high Hex can be manufactured by co-sputtering Pt and Cr.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration showing the film configuration of an exchange-coupled film according to a first embodiment of the present invention;

FIG. 2 is an illustration showing the film configuration of an exchange-coupled film according to a second embodiment of the present invention;

FIG. 3 is a circuit block diagram of a magnetic sensor according to an embodiment of the present invention;

FIG. 4 is a plan view showing magnetic sensing elements 11 used in the magnetic sensor;

FIG. 5 is a graph showing R—H curves of a magnetic sensing element prepared in Example 1;

FIG. 6 is a graph showing R—H curves of a magnetic sensing element prepared in Example 2;

FIG. 7 is a graph showing R—H curves of a magnetic sensing element prepared in Comparative Example 1;

FIG. 8 is a graph showing the Hex of each of exchange-coupled films prepared in Examples 3 to 5;

FIG. 9 is a graph showing the Hex of each of exchange-coupled films prepared in Example 6;

FIGS. 10A to 10C are graphs showing R—H curves of a magnetic sensing element prepared in Example 7;

FIGS. 11A to 11C are graphs showing R—H curves of a magnetic sensing element prepared in Example 8;

FIGS. 12A to 12C are graphs showing R—H curves of a magnetic sensing element prepared in Comparative Example 2;

FIG. 13 is a graph showing the relationship between the percentage of Pt contained in Pt—Cr prepared in each of Reference Example 1 and Reference Example 2 and the Hex;

FIG. 14 is a graph showing the relationship between the percentage of Pt contained in Pt—Cr prepared in each of Reference Example 1 and Reference Example 3 and the Hex;

FIG. 15 is an illustration showing the film configuration of an exchange-coupled film prepared in each of Examples 9 to 12 and Comparative Examples 3 and 4; and

FIG. 16 is a graph showing the relationship between the temperature of an exchange-coupled film prepared in each of Examples 9 to 12 and Comparative Examples 3 and 4 and the Hex.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIG. 1 shows the film configuration of a magnetic sensing element 11 including an exchange-coupled film 10 according to a first embodiment of the present invention.

The magnetic sensing element 11 is formed by stacking a base layer 1, an antiferromagnetic layer 2, a pinned magnetic layer 3, an nonmagnetic material layer 4, a free magnetic layer 5, and a protective layer 6 in that order from a surface of a substrate. The antiferromagnetic layer 2 is composed of a Pt—Cr sublayer 2A and an X—Mn sublayer 2B (where, X is Pt or Ir). The X—Mn sublayer 2B is in contact with the pinned magnetic layer 3. These layers are formed by, for example, a sputtering process or a CVD process. The base layer 1 and the pinned magnetic layer 3 form the exchange-coupled film 10.

The magnetic sensing element 11 is a multilayer element using a so-called single spin valve type of giant magnetoresistive effect (GMR effect) and the electrical resistance thereof varies depending on the relative relation between the vector of the pinned magnetization of the pinned magnetic layer 3 and the vector of magnetization that varies depending on the external magnetic field of the free magnetic layer 5.

The base layer 1 is formed from a Ni—Fe—Cr alloy (nickel-iron-chromium alloy), Cr, Ta, or the like. In the exchange-coupled film 10, the Ni—Fe—Cr alloy is preferable for the purpose of increasing the magnetic field (hereinafter also appropriately referred to as the “Hex”) at which the magnetization of the pinned magnetic layer 3 is reversed.

The antiferromagnetic layer 2 has a multilayer structure composed of the Pt—Cr sublayer 2A and the X—Mn sublayer 2B (where, X is Pt or Ir). In order to increase the Hex, the thickness D1 of the Pt—Cr sublayer 2A is preferably greater than the thickness D2 of the X—Mn sublayer 2B. The ratio of the thickness D1 to the thickness D2 (D1:D2) is preferably 5:1 to 100:1 and more preferably 10:1 to 50:1.

From the viewpoint of increasing the Hex, the Pt—Cr sublayer 2A preferably has a composition represented by the formula Pt_XCr_{100 at %-X} (X is 45 at % to 62 at %) and more preferably a composition represented by the formula Pt_XCr_{100 at %-X} (X is 50 at % to 57 at %). From the same viewpoint, the X—Mn sublayer 2B is preferably a Pt—Mn sublayer.

In this embodiment, the antiferromagnetic layer 2 is regularized by annealing, whereby exchange coupling is induced between (at the interface between) the antiferromagnetic layer 2 and the pinned magnetic layer 3. The exchange coupling increases the strong-magnetic field resistance of the pinned magnetic layer 3 to increase the Hex.

The pinned magnetic layer 3 is formed from a Co—Fe alloy (cobalt-iron alloy). Increasing the content of Fe in the Co—Fe alloy increases the coercive force thereof. The pinned magnetic layer 3 is a layer contributing to the spin valve type of giant magnetoresistive effect. A direction in which the pinned magnetization direction P of the pinned magnetic layer 3 extends is the sensitivity axis direction of the magnetic sensing element 11.

The nonmagnetic material layer 4 can be formed using Cu (copper) or the like.

The free magnetic layer 5 is not limited in material or structure. The free magnetic layer 5 can be formed using, for example, material such as a Co—Fe alloy (cobalt-iron alloy) or a Ni—Fe alloy (nickel-iron alloy) in the form of a single-layer structure, a multilayer structure, or a multilayered ferrimagnetic structure.

The protective layer 6 can be formed using Ta (tantalum).

Second Embodiment

FIG. 2 is an illustration showing the film configuration of a magnetic sensing element 21 including an exchange-coupled film 20 according to a second embodiment of the present invention. In this embodiment, layers having the same function as that of the magnetic sensing element 11 shown in FIG. 1 are given the same reference numerals and will not be described in detail.

In the magnetic sensing element 21, the exchange-coupled film 20 is composed of a pinned magnetic layer 3 with a self-pinned structure and an antiferromagnetic layer 2 joined thereto. The magnetic sensing element 21 differs from the magnetic sensing element 11 shown in FIG. 1 in that a nonmagnetic material layer 4 and a free magnetic layer 5 are placed under the pinned magnetic layer 3.

The magnetic sensing element 21 is also a multilayer element using a so-called single spin valve type of giant magnetoresistive effect. The electrical resistance thereof varies depending on the relative relation between the vector of the pinned magnetization of a first magnetic sublayer 3A of the pinned magnetic layer 3 and the vector of magnetization that varies depending on the external magnetic field of the free magnetic layer 5.

The pinned magnetic layer 3 has a self-pinned structure composed of the first magnetic sublayer 3A, a second magnetic sublayer 3C, and a nonmagnetic intermediate sublayer 3B located between these two sublayers. The pinned magnetization direction P1 of the first magnetic sublayer 3A is antiparallel to the pinned magnetization direction P2 of the second magnetic sublayer 3C because of interaction. The first magnetic sublayer 3A is next to the nonmagnetic material layer 4 and the pinned magnetization direction P1 of the first magnetic sublayer 3A is the pinned magnetization direction of the pinned magnetic layer 3. A direction in which the pinned magnetization direction P1 extends is the sensitivity axis direction of the magnetic sensing element 21.

The first magnetic sublayer 3A and the second magnetic sublayer 3C are formed from an Fe—Co alloy (iron-cobalt alloy). Increasing the content of Fe in the Fe—Co alloy increases the coercive force thereof. The first magnetic sublayer 3A, which is next to the nonmagnetic material layer 4, is a layer contributing to the spin valve type of giant magnetoresistive effect.

The nonmagnetic intermediate sublayer 3B is formed from Ru (ruthenium) or the like. The nonmagnetic intermediate sublayer 3B, which is made of Ru, preferably has a thickness of 3 Å to 5 Å or 8 Å to 10 Å.

Configuration of Magnetic Sensor

FIG. 3 shows a magnetic sensor (magnetic sensing device) 30 including a plurality of magnetic sensing elements identical to the magnetic sensing element 11 shown in FIG. 1.

Referring to FIG. 3, the magnetic sensing elements are different in pinned magnetization direction P (refer to FIG. 1) and are given different reference numerals 11Xa, 11Xb, 11Ya, and 11Yb for discrimination purposes. In the magnetic sensor 30, the magnetic sensing elements 11Xa, 11Xb, 11Ya, and 11Yb are placed on a single substrate.

As shown in FIG. 3, the magnetic sensor 30 includes a full bridge circuit 32X and a full bridge circuit 32Y. The full bridge circuit 32X includes the two magnetic sensing elements 11Xa and the two magnetic sensing elements 11Xb. The full bridge circuit 32Y includes the two magnetic sensing elements 11Ya and two magnetic sensing elements 11Yb. The magnetic sensing elements 11Xa, 11Xb, 11Ya, and 11Yb have the film structure of the exchange-coupled film 10 of the magnetic sensing element 11 shown in FIG. 1. These are hereinafter appropriately referred to as the magnetic sensing elements 11 unless these are discriminated.

The full bridge circuit 32X and the full bridge circuit 32Y include the magnetic sensing elements 11 having different pinned magnetization directions indicated by arrows as shown in FIG. 3 for the purpose of allowing detected magnetic field directions to differ and have the same mechanism for detecting a magnetic field. A mechanism for detecting a magnetic field using the full bridge circuit 32X is described below.

The full bridge circuit 32X is composed of a first series section 32Xa and second series section 32Xb connected in series to each other. The first series section 32Xa is composed of the magnetic sensing elements 11Xa and 11Xb connected in series to each other. The second series section 32Xb is composed of the magnetic sensing elements 11Xb and 11Xa connected in series to each other.

A power-supply voltage Vdd is applied to a power-supply terminal 33 common to the magnetic sensing element 11Xa included in the first series section 32Xa and the magnetic sensing element 11Xb included in the second series section 32Xb. A ground terminal 34 common to the magnetic sensing element 11Xb included in the first series section 32Xa and the magnetic sensing element 11Xa included in the second series section 32Xb is set to the ground potential GND.

The differential output (OutX1)−(OutX2) between the output potential (OutX1) of the midpoint 35Xa of the first series section 32Xa and the output potential (OutX2) of the midpoint 35Xb of the second series section 32Xb is obtained as a detection output (detection output voltage) VXs in an X-direction.

The full bridge circuit 32Y works similarly to the full bridge circuit 32X and therefore the differential output (OutY1)−(OutY2) between the output potential (OutY1) of the midpoint 35Ya of a first series section 32Ya included in the full bridge circuit 32Y and the output potential (OutY2) of the midpoint 35Yb of a second series section 32Yb included in the full bridge circuit 32Y is obtained as a detection output (detection output voltage) VYs in a Y-direction.

As indicated by arrows in FIG. 3, the sensitivity axis direction of each of the magnetic sensing elements 11Xa and 11Xb forming the full bridge circuit 32X is perpendicular to the sensitivity axis direction of each of the magnetic sensing elements 11Ya and 11Yb forming the full bridge circuit 32Y.

As shown in FIG. 3, in the magnetic sensor 30, the orientation of the free magnetic layer 5 of each magnetic sensing element 11 varies so as to follow the direction of an external magnetic field H. In this event, the resistance varies depending on the vector relationship between the pinned magnetization direction P of the pinned magnetic layer 3 and the magnetization direction of the free magnetic layer 5.

Supposing that, for example, the external magnetic field H acts in a direction shown in FIG. 3. The magnetic sensing element 11Xa included in the full bridge circuit 32X exhibits a reduced electrical resistance because the sensitivity axis direction coincides with the direction of the external magnetic field H. However, the magnetic sensing element 11Xb exhibits an increased electrical resistance because the sensitivity axis direction is opposite to the direction of the external magnetic field H. The change of the electrical resistance allows the detection output voltage VXs=(OutX1)−(OutX2) to peak. As the external magnetic field H changes rightward with respect to the plane of FIG. 3, the detection output voltage VXs decreases. As the external magnetic field H changes upward or downward with respect to the plane of FIG. 3, the detection output voltage VXs decreases to zero.

On the other hand, in the full bridge circuit 32Y, when the external magnetic field H is leftward with respect to the plane of FIG. 3, the magnetization direction of the free magnetic layer 5 of every magnetic sensing element 11 is perpendicular to the sensitivity axis direction (pinned magnetization direction P) and therefore the magnetic sensing elements 11Ya and 11Xb exhibit the same resistance. Thus, the detection output voltage VYs is zero. When the external magnetic field H acts downward with respect to the plane of FIG. 3, the detection output voltage VYs=(OutY1)−(OutY2) of the full bridge circuit 32Y peaks. As the external magnetic field H changes upward with respect to the plane thereof, the detection output voltage VYs decreases.

As described above, as the direction of the external magnetic field H changes, the detection output voltage VXs of the full bridge circuit 32X and the detection output voltage VYs of the full bridge circuit 32Y vary. Thus, the movement direction and travel distance (relative position) of a detection target can be detected on the basis of the detection output voltages VXs and VYs obtained from the full bridge circuits 32X and 32Y.

FIG. 3 shows the magnetic sensor 30, which is configured to be capable of detecting a magnetic field in the X-direction and a Y-direction perpendicular to the X-direction. However, the magnetic sensor 30 may be configured to include the full bridge circuit 32X or the full bridge circuit 32Y only so as to detect a magnetic field in the X-direction or the Y-direction, respectively, only.

FIG. 4 shows the planar structure of each of the magnetic sensing elements 11Xa and 11Xb. In FIGS. 3 and 4, a BXa-BXb direction is the X-direction. In FIG. 4, (A) and (B) show the pinned magnetization directions P of the magnetic sensing elements 11Xa and 11Xb as indicated by arrows. The pinned magnetization directions P of the magnetic sensing elements 11Xa and 11Xb are the X-direction and are opposite to each other.

As shown in FIG. 4, the magnetic sensing elements 11Xa and 11Xb each include stripe-shaped element sections 12. The longitudinal direction of each element section 12 is directed in a BYa-BYb direction. A plurality of the element sections 12 are placed in parallel to each other. Illustrated right end portions of the neighboring element sections 12 are connected to each other with conductive sections 13a. Illustrated left end portions of the neighboring element sections 12 are connected to each other with conductive sections 13b. The conductive sections 13a and 13b are alternately connected to the illustrated right and left end portions of the element sections 12, whereby the element sections 12 are coupled to each other in a so-called meander pattern. In the magnetic sensing elements 11Xa and 11Xb, the conductive section 13a shown in a lower right portion is united with a connection terminal 14a and the conductive section 13b shown in an upper left portion is united with a connection terminal 14b.

Each element section 12 is composed of a plurality of stacked metal layers (alloy layers). FIG. 1 shows the multilayer structure of the element section 12. The element section 12 may have a multilayer structure shown in FIG. 2.

In the magnetic sensor 30 shown in FIGS. 3 and 4, the magnetic sensing element 11 can be replaced with the magnetic sensing element 21, shown in FIG. 2, according to the second embodiment.

EXAMPLES

Example 1

A magnetic sensing element 11 (refer to FIG. 1) including an exchange-coupled film 10 having a film configuration below was prepared. In examples, comparative examples, and reference examples below, a parenthesized value is a thickness (Å). The exchange-coupled film 10 was annealed at 400° C. for 5 hours in a magnetic field of 1 kOe, whereby the magnetization of each of a pinned magnetic layer 3 and an antiferromagnetic layer 2 was pinned.

Substrate/base layer 1: Ni—Fe—Cr (60)/antiferromagnetic layer 2 [Pt—Cr sublayer 2A: Pt_{51 at %}-Cr_{49 at %} (280)/X—Mn sublayer 2B: Pt_{50 at %}-Mn_{50 at %} (20)]/pinned magnetic layer 3: Co_{90 at %}-Fe_{10 at %} (50)/nonmagnetic material layer 4: Cu (40)/free magnetic layer 5: Co_{90 at %}-Fe_{10 at %} (15)/Ni_{81.5 at %}-Fe_{18.5 at %} (30)/protective layer 6: Ta (50)

Example 2

A magnetic sensing element 11 including an exchange-coupled film 10 having a film configuration below was prepared by changing a Pt—Cr sublayer 2A of an antiferromagnetic layer 2 from Pt_{51 at %}-Cr_{49 at %} (280) prepared in Example 1 to Pt_{54 at %}-Cr_{46 at %} (280).

Substrate/base layer 1: Ni—Fe—Cr (60)/antiferromagnetic layer 2 [Pt—Cr sublayer 2A: Pt_{54 at %}-Cr_{46 at %} (280)/X—Mn sublayer 2B: Pt_{50 at %}-Mn_{50 at %} (20)]/pinned magnetic layer 3: Co_{90 at %}-Fe_{10 at %} (50)/nonmagnetic material layer 4: Cu (40)/free magnetic layer 5: Co_{90 at %}-Fe_{10 at %} (15)/Ni_{81.5 at %}-Fe_{18.5 at %} (30)/protective layer 6: Ta (50)

Comparative Example 1

A magnetic sensing element 11 including an exchange-coupled film 10 having a film configuration below was prepared by changing an antiferromagnetic layer 2 from [Pt—Cr sublayer 2A: Pt_{51 at %}-Cr_{49 at %} (280)/X—Mn sublayer 2B: Pt_{50 at %}-Mn_{50 at %} (20)] prepared in Example 1 to Pt_{50 at %}-Mn_{50 at %} (300).

Substrate/base layer 1: Ni—Fe—Cr (60)/antiferromagnetic layer 2: Pt_{50 at %}-Mn_{50 at %} (300)/pinned magnetic layer 3: Co_{90 at %}-Fe_{10 at %} (50)/nonmagnetic material layer 4: Cu (40)/free magnetic layer 5: Co_{90 at %}-Fe_{10 at %} (15)/Ni_{81.5 at %}-Fe_{18.5 at %} (30)/protective layer 6: Ta (50)

Application of External Magnetic Field

An external magnetic field H was applied to the magnetic sensing element 11 prepared in each of Example 1, Example 2, and Comparative Example 1 from a direction parallel to the pinned magnetization direction (a P-direction in FIG. 1) of the pinned magnetic layer 3 of the exchange-coupled film 10, whereby the rate (rate of change in resistance) ΔMR (ΔR/R) at which the electrical resistance R was changed by the magnetic field H was determined.

FIG. 5, FIG. 6, and FIG. 7 show R—H curves of the magnetic sensing element 11 prepared in Example 1, R—H curves of the magnetic sensing element 11 prepared in Example 2, and R—H curves of the magnetic sensing element 11 prepared in Comparative Example 1, respectively. In each of these figures, the horizontal axis represents the intensity [Oe] of the magnetic field H, the vertical axis represents the rate of change in resistance ΔMR [%], a curve (a curve located on a lower side at H=1,000 [Oe]) marked “Inc.” represents ΔMR in the case of increasing the magnetic field H, and a curve (a curve located on an upper side at H=1,000 [Oe]) marked “Dec.” represents ΔMR in the case of reducing the magnetic field H.

Referring to FIGS. 5 to 7, hysteresis appears in the variation curve “Inc.” of the rate of change in resistance ΔMR [o] in the case of changing the magnetic field to a positive side and the variation curve “Dec.” of the rate of change in resistance ΔMR [o] in the case of changing the magnetic field to a negative side and the median of the full width at half maximum of each of the variation curve “Inc.” and the variation curve “Dec.” substantially coincides with the magnetic field (Hex) at which the magnetization direction of a pinned magnetic layer is reversed.

It was clear that the magnetic sensing element 11 prepared in Example 1 and the magnetic sensing element 11 prepared in Example 2 exhibited a higher magnetic field (Hex) as compared to the magnetic sensing element 11 prepared in Comparative Example 1. That is, the magnetic sensing elements 11 including the exchange-coupled films 10 prepared in Examples 1 and 2 can sufficiently measure a magnetic field in a strong-magnetic field environment.

Example 3

Exchange-coupled films 10 (refer to FIG. 1) having a film configuration below were prepared by varying the thickness D1 of a Pt—Cr sublayer 2A of an antiferromagnetic layer 2 and the thickness D2 of a Pt—Mn sublayer 2B thereof. The exchange-coupled films 10 were annealed at 400° C. for 5 hours in a magnetic field of 1 kOe, whereby the magnetization of each of a pinned magnetic layer 3 and the antiferromagnetic layer 2 was pinned.

Substrate/base layer 1: Ni—Fe—Cr (60)/antiferromagnetic layer 2 [Pt—Cr sublayer 2A: Pt_{54 at %}-Cr_{46 at %} (300−x)/X—Mn sublayer 2B: Pt_{50 at %}-Mn_{50 at %} (x)]/pinned magnetic layer 3: Co_{90 at %}-Fe_{10 at %} (50)/nonmagnetic material layer 4: Cu (40)/free magnetic layer 5: Co_{90 at %}-Fe_{10 at %} (15)/Ni_{81.5 at %}-Fe_{18.5 at %} (30)/protective layer 6: Ta (50)

For each exchange-coupled film 10 including the Pt—Cr sublayer 2A and Pt—Mn sublayer having a thickness shown in Table 1, the Hex calculated from an R—H curve was as described below. Hereinafter, Pt_{54 at %}-Cr_{46 at %} is appropriately referred to as 54Pt—Cr, Pt_{51 at %}-Cr_{49 at %} is appropriately referred to as 51Pt—Cr, and Pt_{50 at %}-Mn_{50 at %} is appropriately referred to as Pt—Mn.

TABLE 1
Thickness of 54Pt—Cr	Thickness of Pt—Mn
sublayer	sublayer	Hex at room temperature
D1 [Å] (300 − x)	D2 [Å] (x)	Hex [Oe]
300	0	238
298	2	364
296	4	519
294	6	634
292	8	790
290	10	917
288	12	1033
286	14	1149
284	16	1263
282	18	1348
280	20	1430
278	22	1462
276	24	1463
274	26	1466
272	28	1423
270	30	1372
266	34	1034
262	38	842
250	50	721
200	100	620
100	200	724
0	300	590

Example 4

Exchange-coupled films 10 having a film configuration below were prepared by changing a Pt—Cr sublayer 2A of an antiferromagnetic layer 2 from 54Pt—Cr (280-x) prepared in Example 3 to 51Pt—Cr (280-x). The exchange-coupled films 10 were annealed at 400° C. for 5 hours in a magnetic field of 1 kOe, whereby the magnetization of each of a pinned magnetic layer 3 and the antiferromagnetic layer 2 was pinned.

Substrate/base layer 1: Ni—Fe—Cr (60)/antiferromagnetic layer 2 [Pt—Cr sublayer 2A: Pt_{51 at %}-Cr_{49 at %} (300-x)/X—Mn sublayer 2B: Pt_{50 at %}-Mn_{50 at %} (x)]/pinned magnetic layer 3: Co_{90 at %}-Fe_{10 at %} (50)/nonmagnetic material layer 4: Cu (40)/free magnetic layer 5: Co_{90 at %}-Fe_{10 at %} (15)/Ni_{81.5 at %}-Fe_{18.5 at %} (30)/protective layer 6: Ta (50)

For each exchange-coupled film 10 including the Pt—Cr sublayer 2A and Pt—Mn sublayer having a thickness shown in Table 2, the Hex calculated from an R—H curve was as described below.

TABLE 2
Thickness of 51Pt—Cr	Thickness of Pt—Mn	Hex at room temperature
sublayer D1 [Å]	sublayer D2 [Å]	Hex [Oe]
300	0	111
296	4	298
292	8	522
288	12	717
284	16	893
280	20	1039
276	24	1141
272	28	1113
250	50	610
200	100	523
100	200	663
0	300	590

Example 5

Exchange-coupled films 10 having the same film configuration as that of Example 4 were prepared and the temperature of annealing was changed from 400° C. of Example 4 to 350° C.

For each exchange-coupled film 10 including a 51Pt—Cr sublayer and Pt—Mn sublayer having a thickness shown in Table 3, the Hex calculated from an R—H curve was as described below.

TABLE 3
Thickness of 51Pt—Cr	Thickness of Pt—Mn	Hex at room temperature
sublayer D1 [Å]	sublayer D2 [Å]	Hex [Oe]
300	0	210
296	4	407
292	8	709
288	12	840
284	16	951
280	20	1056
276	24	1064
272	28	1131
250	50	740
200	100	600
100	200	688
0	300	612

FIG. 8 is a graph showing the Hex of each of the exchange-coupled films 10 prepared in Examples 3 to 5. In this figure, the horizontal axis represents the thickness of a Pt—Mn sublayer (Pt—Mn thickness, [Å]) and the vertical axis represents the Hex [Oe] of an exchange-coupled film. As is clear from FIG. 8 and Tables 1 to 3, using either of 51Pt—Cr and 54Pt—Cr as a Pt—Cr sublayer allows the exchange-coupled films 10 to exhibit a higher Hex as compared to those including an antiferromagnetic layer composed of a Pt—Mn sublayer only.

From the viewpoint of allowing an exchange-coupled film 10 to have a high Hex, 54Pt—Cr is preferably used as a Pt—Cr sublayer. Even if the annealing temperature is 350° C., an exchange-coupled film 10 having substantially the same Hex as that at 400° C. is obtained. Therefore, from the viewpoint of reducing the annealing temperature, 51Pt—Cr is preferably used as a Pt—Cr sublayer.

Example 6

Exchange-coupled films 10 having a film configuration below were prepared by changing an X—Mn sublayer 2B of an antiferromagnetic layer 2 from Pt—Mn prepared in Example 3 to Ir—Mn. The exchange-coupled films 10 were annealed at 400° C. for 5 hours in a magnetic field of 1 kOe, whereby the magnetization of each of a pinned magnetic layer 3 and the antiferromagnetic layer 2 was pinned.

Substrate/base layer 1: Ni—Fe—Cr (60)/antiferromagnetic layer 2 [Pt—Cr sublayer 2A: Pt_{54 at %}-Cr_{46 at %} (300-x)/X—Mn sublayer 2B: Ir_{50 at %}-Mn_{50 at %} (x)]/pinned magnetic layer 3: Co_{90 at %}-Fe_{10 at %} (50)/nonmagnetic material layer 4: Cu (40)/free magnetic layer 5: Co_{90 at %}-Fe_{10 at %} (15)/Ni_{81.5 at %}-Fe_{18.5 at %} (30)/protective layer 6: Ta (50)

For each exchange-coupled film 10 including a Pt—Cr sublayer and Ir—Mn sublayer having a thickness shown in Table 4, the Hex calculated from an R—H curve was as described below.

TABLE 4
Thickness of Pt—Cr	Thickness of Ir—Mn	Hex at room temperature
sublayer D1 [Å]	sublayer D2 [Å]	Hex [Oe]
300	0	238
298	2	283
296	4	293
294	6	281
292	8	199
290	10	156
280	20	85
260	40	167
0	80	162

FIG. 9 is a graph showing the Hex of each of the exchange-coupled films 10 prepared in Example 6. In this figure, the horizontal axis represents the thickness of an Ir—Mn sublayer (Ir—Mn thickness [Å]) and the vertical axis represents the Hex [Oe] of an exchange-coupled film. As is clear from FIG. 9 and Table 4, the effect of increasing the Hex of a Pt—Cr sublayer is provided by an antiferromagnetic layer combined with Ir—Mn similarly to a Pt—Mn sublayer.

Example 7

A magnetic sensing element 21 (refer to FIG. 2) including an exchange-coupled film 20 having a film configuration below was prepared. A parenthesized value is a thickness (Å) The exchange-coupled film 20 was annealed at 350° C. for 5 hours in no magnetic field and was thereby stabilized.

Substrate/base layer 1: Ni—Fe—Cr (42)/free magnetic layer 5: Ni_{81.5 at %}-Fe_{18.5 at %} (18)/:Co_{90 at %}-Fe_{10 at %} (14)/nonmagnetic material layer 4: Cu (30)/pinned magnetic layer 3 [first magnetic sublayer 3A: Co_{90 at %}-Fe_{10 at %} (24)/nonmagnetic intermediate sublayer 3B: Ru (3.6)]/second magnetic sublayer 3C: Fe_{60 at %}-Co_{40 at %} (17)/antiferromagnetic layer 2 [X—Mn sublayer: Pt_{50 at %}-Mn_{50 at %} (20)/Pt_{51 at %}-Cr_{49 at %} (280)]/protective layer 6: Ta (90)

Example 8

A magnetic sensing element 21 including an exchange-coupled film 20 having a film configuration below was prepared by changing an antiferromagnetic layer 2 from [X—Mn sublayer: Pt—Mn (20)/51Pt—Cr (280)] prepared in Example 7 to [X—Mn sublayer: Ir—Mn (4)/51Pt—Cr (296)].

Substrate/base layer 1: Ni—Fe—Cr (42)/free magnetic layer 5: Ni_{81.5 at %}-Fe_{18.5 at %} (18)/:Co_{90 at %}-Fe_{10 at %} (14)/nonmagnetic material layer 4: Cu (30)/pinned magnetic layer 3 [first magnetic sublayer 3A: Co_{90 at %}-Fe_{10 at %} (24)/nonmagnetic intermediate sublayer 3B: Ru (3.6)]/second magnetic sublayer 3C: Fe_{60 at %}-Co_{40 at %} (17)/antiferromagnetic layer 2 [X—Mn sublayer: Ir_{50 at %}-Mn_{50 at %} (4)/Pt_{51 at %}-Cr_{49 at %} (296)]/protective layer 6: Ta (90)

Comparative Example 2

A magnetic sensing element 21 including an exchange-coupled film 20 having a film configuration below was prepared by changing an antiferromagnetic layer 2 from [X—Mn sublayer: Pt—Mn (20)/51Pt—Cr (280)] prepared in Example 7 to Pt—Mn (300).

Substrate/base layer 1: Ni—Fe—Cr (42)/free magnetic layer 5: Ni_{81.5 at %}-Fe_{18.5 at %} (18)/:Co_{90 at %}-Fe_{10 at %} (14)/nonmagnetic material layer 4: Cu (30)/pinned magnetic layer 3 [first magnetic sublayer 3A: Co_{90 at %}-Fe_{10 at %} (24)/nonmagnetic intermediate sublayer 3B: Ru (3.6)]/second magnetic sublayer 3C: Fe_{60 at %}-Co_{40 at %} (17)/antiferromagnetic layer 2: Pt_{50 at %}-Mn_{50 at %} (300)/protective layer 6: Ta (90)

Application of External Magnetic Field

An external magnetic field H was applied to the magnetic sensing element 21 prepared in each of Example 7, Example 8, and Comparative Example 2 from a direction parallel to the pinned magnetization direction (a P1 direction in FIG. 2) of the pinned magnetic layer 3, whereby the rate of change in resistance ΔMR (ΔR/R) was determined.

FIGS. 10A to 10C, FIGS. 11A to 11C, and FIGS. 12A to 12C show R—H curves of the magnetic sensing element 21 prepared in Example 7, R—H curves of the magnetic sensing element 21 prepared in Example 8, and R—H curves of the magnetic sensing element 21 prepared in Comparative Example 2, respectively. In each of these figures, the horizontal axis represents the intensity [Oe] of the magnetic field H, the vertical axis represents ΔMR (%), a curve marked “Inc.” represents ΔMR in the case of increasing the magnetic field H, and a curve marked “Dec.” represents ΔMR in the case of reducing the magnetic field H.

FIGS. 10A to 10C and FIGS. 11A to 11C show less hysteresis as compared to FIGS. 12A to 12C and show an improvement in a ΔMR reduction process down to +5 kOe. This result shows that an antiferromagnetic layer which is composed of a Pt—Cr sublayer and a Pt—Mn sublayer and in which the Pt—Mn sublayer is in contact with a pinned magnetic layer enhances the stabilization of an exchange-coupled film even when the pinned magnetic layer is a self-pinned layer including a first magnetic sublayer, intermediate sublayer, and second magnetic sublayer which are stacked.

Reference Example 1

Magnetic sensing elements having a film configuration below were prepared. A parenthesized value is a thickness (Å). Each exchange-coupled film 10 was annealed at 400° C. for 5 hours in a magnetic field of 1 kOe, whereby the magnetization of each of a pinned magnetic layer 3 and an antiferromagnetic layer 2 were pinned.

Substrate/base layer 1: Ni—Fe—Cr (60)/antiferromagnetic layer 2: Pt_XCr_{100 at %-X} (300)/pinned magnetic layer 3: Co_{90 at %}-Fe_{10 at %} (50)/nonmagnetic material layer 4: Cu (40)/free magnetic layer 5: [Co_{90 at %}-Fe_{10 at %} (15)/81.5Ni—Fe (30)]/protective layer 6: Ta (50)

By co-sputtering Pt and Cr, Pt_XCr_{100 at %-X} (300) films having different Pt-to-Cr ratios were prepared.

Reference Example 2

Pt_XCr_{100 at %-X} (300) films having different Pt-to-Cr ratios were prepared in substantially the same manner as that used in Reference Example 1 except that Pt and Cr were alternately stacked instead of co-sputtering Pt and Cr.

Reference Example 3

Pt_XCr_{100 at %-X} (300) films having different Pt-to-Cr ratios were prepared in substantially the same manner as that used in Example 1 except that a base layer 1 was changed from Ni—Fe—Cr (60) prepared in Example 1 to Ta (50).

Sputtering and Alternate Stacking

FIG. 13 is a graph showing the relationship between the percentage of Pt contained in Pt—Cr prepared in each of Reference Example 1 (co-sputtering) and Reference Example 2 (alternate stacking) and the Hex. As is clear from this figure, Reference Example 1, in which Pt_XCr_{100 at %-X} films were formed by co-sputtering, provides a higher Hex as compared to Reference Example 2, in which Pt_XCr_{100 at %-X} films were formed by alternate stacking, within the Pt percentage range of 51 at % to 57 at %.

Base Layer

FIG. 14 is a graph showing the relationship between the percentage of Pt contained in Pt—Cr prepared in each of Reference Example 1 and Reference Example 3 and the Hex. As is clear from this figure, exchange-coupled films Reference Example 1 (Ni—Fe—Cr base) exhibits a significantly higher Hex as compared to Reference Example 3 (Ta base) within the Pt percentage range of 51 at % to 57 at %.

Example 9

In order to investigate the relationship between the temperature and the Hex, an exchange-coupled film 40 having a structure shown in FIG. 15 was prepared.

Substrate/base layer 1: Ni—Fe—Cr (42)/antiferromagnetic layer 2/pinned magnetic layer 3: 90Co—Fe (100)/protective layer 6: Ta (90)

The exchange-coupled film 40 was formed by setting an antiferromagnetic layer 2 to 51Pt—Cr (280)/Pt—Mn (20) and was annealed at 350° C. for 5 hours in a magnetic field of 1 kOe such that the magnetization of each of a pinned magnetic layer 3 and the antiferromagnetic layer 2 was pinned.

Comparative Example 3

An exchange-coupled film 40 was formed by setting an antiferromagnetic layer 2 to 51Pt—Cr (300) and was annealed at 350° C. for 5 hours in a magnetic field of 1 kOe such that the magnetization of each of a pinned magnetic layer 3 and the antiferromagnetic layer 2 was pinned.

Table 5 shows results obtained by measuring the exchange-coupled film 40 prepared in each of Example 9 and Comparative Example 3 for a change in Hex due to a change in temperature. In Tables 5 to 7, Tb represents the temperature at which the Hex vanishes and Hex (200° C. or 300° C.)/Hex (room temperature) represents a normalized value obtained by dividing the Hex at 200° C. or 300° C. by the Hex at room temperature.

TABLE 5
Thickness of	Thickness
51Pt—Cr	of Pt—Mn		Hex (200° C.)/	Hex (300° C.)/
sublayer	sublayer	Tb	Hex (room	Hex (room
D1 [Å]	D2 [Å]	(° C.)	temperature)	temperature)
300	0	460	0.96	0.66
280	20	>500	0.88	0.75

Example 10

An exchange-coupled film 40 was formed by setting an antiferromagnetic layer 2 to 51Pt—Cr (280)/Pt—Mn (20) and was annealed at 400° C. for 5 hours in a magnetic field of 1 kOe such that the magnetization of each of a pinned magnetic layer 3 and the antiferromagnetic layer 2 was pinned.

Comparative Example 4

An exchange-coupled film 40 was formed by setting an antiferromagnetic layer 2 to Pt—Mn (300) and was annealed at 400° C. for 5 hours in a magnetic field of 1 kOe such that the magnetization of each of a pinned magnetic layer 3 and the antiferromagnetic layer 2 was pinned.

Table 6 shows measurement result of Example 10 and Comparative Example 4.

TABLE 6
	Thickness
Thickness of	of Pt—Mn		Hex (200° C.)/	Hex (300° C.)/
51Pt—Cr sublayer	sublayer	Tb	Hex (room	Hex (room
D1 [Å]	D2 [Å]	(° C.)	temperature)	temperature)
280	20	>500	0.86	0.76
0	300	400	0.82	0.35

Example 11

An exchange-coupled film 40 was formed by setting an antiferromagnetic layer 2 to 54Pt—Cr (290)/Pt—Mn (10) and was annealed at 400° C. for 5 hours in a magnetic field of 1 kOe such that the magnetization of each of a pinned magnetic layer 3 and the antiferromagnetic layer 2 was pinned.

Example 12

An exchange-coupled film 40 was formed by setting an antiferromagnetic layer 2 to 54Pt—Cr (280)/Pt—Mn (20) and was annealed at 400° C. for 5 hours in a magnetic field of 1 kOe such that the magnetization of each of a pinned magnetic layer 3 and the antiferromagnetic layer 2 was pinned.

Table 7 shows measurement result of Examples 11 and 12 and Comparative Example 4.

TABLE 7
	Thickness
Thickness of	of Pt—Mn		Hex (200° C.)/	Hex (300° C.)/
54Pt—Cr sublayer	sublayer	Tb	Hex (room	Hex (room
D1 [Å]	D2 [Å]	(° C.)	temperature)	temperature)
290	10	500	0.98	0.86
280	20	>500	0.91	0.80
0	300	400	0.82	0.35

FIG. 16 is a graph showing the relationship between the temperature of the exchange-coupled film 40 prepared in each of Examples 9 to 12 and Comparative Examples 3 and 4 and the Hex. This graph shows results obtained by measuring the quantity corresponding to the Hex in the R—H curve of each of FIGS. 5 to 7 using a VSM (vibrating sample magnetometer).

As shown in FIG. 16 and Tables 5 to 7, an exchange-coupled film 40 including an antiferromagnetic layer 2 including a Pt—Mn sublayer and a Pt—Cr sublayer inserted therein exhibited higher Tb as compared to an exchange-coupled film including an antiferromagnetic layer 2 made of Pt—Mn only and also exhibited high stability under high-temperature conditions for maintaining high Hex.

Claims

1. An exchange-coupled film comprising

an antiferromagnetic layer composed of a Pt—Cr sublayer and an X—Mn sublayer (where X is Pt or Ir); and

a pinned magnetic layer, the antiferromagnetic layer and the pinned magnetic layer being stacked,

wherein the X—Mn sublayer of the antiferromagnetic layer is in contact with the pinned magnetic layer.

2. The exchange-coupled film according to claim 1, wherein the pinned magnetic layer is a self-pinned layer including a first magnetic sublayer, intermediate sublayer, and second magnetic sublayer which are stacked.

3. The exchange-coupled film according to claim 1, wherein the thickness of the Pt—Cr sublayer is greater than the thickness of the X—Mn sublayer.

4. The exchange-coupled film according to claim 3, wherein the ratio of the thickness of the Pt—Cr sublayer to the thickness of the X—Mn sublayer is 5:1 to 100:1.

5. The exchange-coupled film according to claim 1, wherein the Pt—Cr sublayer has a composition represented by the formula PtXCr100 at %-X (X is 45 at % to 62 at %).

6. The exchange-coupled film according to claim 1, wherein the Pt—Cr sublayer has a composition represented by the formula PtXCr100 at %-X (X is 50 at % to 57 at %).

7. The exchange-coupled film according to claim 1, further comprising a base layer next to the antiferromagnetic layer, wherein the base layer is made of Ni—Fe—Cr.

8. A magnetoresistive element comprising the exchange-coupled film according to claim 1 and a free magnetic layer, the exchange-coupled film and the free magnetic layer being stacked.

9. A magnetic sensing device comprising the magnetoresistive element according to claim 8.

10. The magnetic sensing device according to claim 9, further comprising a plurality of magnetoresistive elements, placed on a single substrate, identical to the magnetoresistive element according to claim 8, wherein the magnetoresistive elements include those having different pinned magnetization directions.

11. A method for manufacturing the exchange-coupled film according to claim 1, comprising forming the Pt—Cr sublayer by a process for co-sputtering Pt and Cr.