Abstract: A resistive electromagnet assembly comprises a pair of coils with a gap defined between the coils. The resistive electromagnet assembly is configured to generate a field having a magnetic flux density of at least about 4 Tesla and at a sweep rate to complete a hysteresis loop in less than about 1 minute. A support assembly is configured to support a sample of magnetic material within the gap. An optics module is configured to expose a test region of the magnetic material sample to an optical beam probe while the test region is subjected to the field and to receive a reflected beam from the test region. A processor is coupled to the optics module and configured to measure one or more properties of the magnetic material using the received reflected beam.

Abstract: Determining a Curie temperature (Tc) distribution of a sample comprising magnetic material involves subjecting the sample to an electromagnetic field, heating the sample over a range of temperatures, generating a signal representative of a parameter of the sample that changes as a function of changing sample temperature while the sample is subjected to the electromagnetic field, and determining the Tc distribution of the sample using the generated signal and a multiplicity of predetermined parameters of the sample.

Abstract: An optical profiler for an ultra-smooth surface, such as a magnetic recording disk, provides for a normally incident beam deflection against the target surface to be profiled. A linearly polarized laser light of a first polarization is focused on the target surface in a normally incident direction. The beam is reflected back along its original path from the focal point. Optics are provided that change the polarization of the reflected beam to a second polarization. A reflected beam, with a second polarization, is directed onto a position sensitive detector for evaluation.

Abstract: An arrangement and method for reliably finding the wave form extrema of interference signals produced by a quadrature phase shift interferometer (QPSI) takes advantage of the quadrature property of I and Q signals. The zero-crossing points in the I and Q signals are determined. Peak detection is performed for peaks and valleys in the Q signal in close proximity to the zero-crossing points in the I signal, and for peaks and valleys in the I signal in close proximity to the zero-crossing points in the Q signal. These represent the maximum and minimum points of the I and Q signals. From these points, intensity envelopes are created and QPSI phase wrapping is performed to determine the phase angle and ultimately, out-of-plane displacement may be determined.

Abstract: An arrangement and method of measuring head-media spacing modulation (HMS_Wq) removes the portion of out-of-plane motion caused by disk modes from the dynamic measurements of hard disk surface topography. Employing time-domain measurement techniques, circumferential surface topographical measurements are made for a hard disk surface. A boundary wavelength is determined, and a first partial HMS_Wq value is determined based upon measurements taken at a first disk rotational speed. A second partial HMS_Wq value is determined based upon measurements taken at a second disk rotational speed. The first and second partial HMS_Wq values are combined to provide a complete and accurate HMS_Wq value, taking advantage of the principle that the disk mode location in the spatial domain topography spectrum converted from the measured time-domain data shifts when the disk rotation speed is changed during the measurement.

Abstract: A method and arrangement for measuring head-media spacing modulation (HMS_Wq) employs a profilometer to measure the surface topography of a disk. A cumulative power spectral density (PSD) distribution is generated from the measured surface topography. Discontinuities and steps are identified in the PSD distribution. The discontinuities and steps are removed to create a corrected PSD distribution. A noise free spectrum is then reconstructed from the corrected PSD distribution.

Abstract: A method and apparatus for using a dual-beam interferometer to test surface flatness is provided. The interferometer directs two beams focused at distinct points on a testing surface, such as the surface of a magnetic recording disc. An offset distance “d” between the two beams is provided on the target surface. In the present invention, the separation distance “d” is adjustable. The feature of adjustable separation distance in the interferometer allows the interferometer to meet the different spatial frequency requirements of various applications. In operation, first and second reflected beams are returned to an intensity beam splitter, where they are split and then recombined into two new beams of substantially equal intensity. The second of the two new light beams is constructed by the interference of half intensity of the first and half intensity of second beams, and is sent to a photodiode.

Abstract: The present invention provides a method for detecting missing servo patterns on printed recording media. In general, the method first comprises the step of generating a map of anticipated servo burst patterns for a magnetic medium. The magnetic medium is typically a magnetic storage disc. Next, the magnetic medium is placed onto a disc reading assembly. Using the disc reading assembly, individual servo bursts on the magnetic medium are identified. In one embodiment, signals from the magnetic medium are processed through a frequency down conversion process, coupled with band pass filtering and rms-to-DC conversion. This enables higher throughput of signal processing. A map of identified servo bursts on the magnetic medium can then be generated. The map of identified servo bursts is then compared with the map of anticipated servo burst patterns. In this way, missing servo bursts can be detected.

Abstract: A method and apparatus for using a dual-beam interferometer to test surface flatness is provided. The interferometer directs two beams focused at distinct points on a testing surface, such as the surface of a magnetic recording disc. An offset distance “d” between the two beams is provided on the target surface. In the present invention, the separation distance “d” is adjustable. The feature of adjustable separation distance in the interferometer allows the interferometer to meet the different spatial frequency requirements of various applications. In operation, first and second reflected beams are returned to an intensity beam splitter, where they are split and then recombined into two new beams of substantially equal intensity. The second of the two new light beams is constructed by the interference of half intensity of the first and half intensity of second beams, and is sent to a photodiode.

Abstract: A method and arrangement for measuring head-media spacing modulation (HMS_Wq) employs a profilometer to measure the surface topography of a disk. A cumulative power spectral density (PSD) distribution is generated from the measured surface topography. Discontinuities and steps are identified in the PSD distribution. The discontinuities and steps are removed to create a corrected PSD distribution. A noise free spectrum is then reconstructed from the corrected PSD distribution.

Abstract: An arrangement and method of measuring head-media spacing modulation (HMS_Wq) removes the portion of out-of-plane motion caused by disk modes from the dynamic measurements of hard disk surface topography. Employing time-domain measurement techniques, circumferential surface topographical measurements are made for a hard disk surface. A boundary wavelength is determined, and a first partial HMS_Wq value is determined based upon measurements taken at a first disk rotational speed. A second partial HMS_Wq value is determined based upon measurements taken at a second disk rotational speed. The first and second partial HMS_Wq values are combined to provide a complete and accurate HMS_Wq value, taking advantage of the principle that the disk mode location in the spatial domain topography spectrum converted from the measured time-domain data shifts when the disk rotation speed is changed during the measurement.

Abstract: An optical profiler for an ultra-smooth surface, such as a magnetic recording disk, provides for a normally incident beam deflection against the target surface to be profiled. A linearly polarized laser light of a first polarization is focused on the target surface in a normally incident direction. The beam is reflected back along its original path from the focal point. Optics are provided that change the polarization of the reflected beam to a second polarization. A reflected beam, with a second polarization, is directed onto a position sensitive detector for evaluation.

Abstract: A method and apparatus for interferometnc measurement of a medium surface is disclosed. More particularly, a quadrature phase shift interferometer and a process for unwrapping phase are described. The interferometer has a reduced number of optical components though yields results sufficient to measure surface of a hard disc for final inspection. Defects on such a surface are characterized by their out-of-plane displacement with nanometer resolution.

Abstract: A method and apparatus for interferometric measurement of a medium surface is disclosed. More particularly, a quadrature phase shift interferometer and a process for unwrapping phase are described. The interferometer has a reduced number of optical components though yields results sufficient to measure surface of a hard disc for final inspection. Defects on such a surface are characterized by their out-of-plane displacement with nanometer resolution.

Abstract: An apparatus and a method for measuring the magnetic properties of recording media. Particularly, the invention is directed to the measurement of the coercivity of recording media having high coercivity values. The apparatus for measuring the magnetic properties of recording media contains a thermal source to increase the temperature of a selected portion of the recording media, thus temporally decreasing the coercivity of the recording media in the selected portion. Magnetic transitions are induced by applying a magnetic field to the regions of the medium affected by the thermal source. The electromagnet applies an incrementally increasing DC field to the selected portion to generate variable magnetization data.

Abstract: Processing two interference signals to reconstruct a target image includes splitting a laser beam into a reference beam and a measurement beam, and in turn splitting the reference beam into two sub-reference beams. A phase shift is introduced into one of the sub-reference beams, the phase shift being substantially 90 degrees. A measurement beam is reflected from a surface of a moving target, and split into two sub-measurement beams. A first respective sub-reference beam is combined with a first sub-measurement beam, and the second sub-reference beam is combined with the second sub-measurement beam, and the in phase and out of phase signals reconstruct the target surface. Adjustment of the split sub-reference beams is effected by Pockels cells to achieve the desired phase difference between the two sub-reference beams. The reconstructed motion of the target surface is effected with a selected frequency characteristic, spatial resolution and range characteristic.

Abstract: A system for magnetically evaluating magnetic data storage media includes a spindle for rotatably supporting magnetic disks, a read/write transducer, and an erasing transducer, both supported for radial movement relative to the disk. The read/write transducer records a sequence of magnetically isolated transitions. When sensing the sequence, the read/write transducer generates a fringing field signal which is low pass filtered and RMS processed to provide a voltage proportional to the remanence-thickness product. The erasing transducer is a ring head transducer having a substantially larger gap and transducer/disk spacing as compared to an aerodynamically supported transducer. Consequently a Hall effect probe is positionable within the gap to directly measure the magnetic intensities of erase fields.

Abstract: A system is disclosed for detecting local surface discontinuities in magnetic data storage disks. The system includes a spindle that rotatably supports a magnetic disk being tested. An interferometer generates a laser beam which is guided through an optics assembly supported above the magnetic disk, for linear movement radially of the disk. The combined radial and linear movement causes the laser beam to trace a spiral scanning path on the disk surface. The disk surface scatters the laser energy, a portion of which is returned to the interferometer and caused to interfere with a reference beam. The resulting interference intensity fluctuates in response to changes in the optical path length, thus measuring topographies of the discontinuities. A discontinuity recognition triggering pulse can be positioned in time with respect to indexing pulses, to identify the location of the associated discontinuity radially and angularly of the disk.

Abstract: This invention relates to an instrument or device capable of performing a non-destructive evaluation of the major magnetic properties of a recording disc member that determines the basic digital recording performance of said member. These measurements include the non-destructive evaluation of parameters including coercive force and remanence-thickness product of the recording member as a function of the circumference and/or the radius of the recording member. These parameters determine the signal amplitude as well as the frequency response of the disc member.