Abstract: Disclosed is a magnetic material comprising a crystal of ?-GaxFe2-xO3 (wherein 0<x<1) prepared by substituting a part of Ga3+ ion sites of an ?-Fe2O3 crystal with Fe3+ ions and having X-ray diffraction peaks corresponding to the crystal structure of ?-Fe2O3. The coercive force of the magnetic material lowers in accordance with the Ga content thereof, and the saturation magnetization thereof has a maximum value.

Abstract: [Problem] When a nonreciprocal device operating at 100 GHz to 300 GHz is to be realized by using a conventional magnetic material of garnet-type ferrite or spinel-type ferrite, a huge permanent magnet is required and, therefore, it is very difficult to achieve a millimeter-wave band nonreciprocal device for practical use. [Solving means] To solve this problem, there is provided a millimeter-wave band nonreciprocal device composed of a magnetic material represented by a formula ?-MxFe2-xO3 (0<x<2), wherein M is at least one of elements In, Ga, Al, Sc, Cr, Sm, Yb, Ce, Ru, Rh, Ti, Co, Ni, Mn, Zn, Zr, and Y and the magnetic material having ?-phase hematite as a principal phase exhibits strong coercive force and anisotropic magnetic field at room temperature. Dimensions of a magnetic circuit containing a permanent magnet for operations of the nonreciprocal device can be made remarkably small and, by optimum design, the use of the magnetic circuit can be made unnecessary.

Abstract: A magnetic material is provided that has an iron oxide phase whose principal phase is a crystal of a structure which has the same space group as ?-Fe2O3 crystal and in which Al is substituted for a portion of the Fe sites of the ?-Fe2O3 crystal. The molar ratio of Al to Fe in the iron oxide phase, when expressed as Al:Fe=x:(2?x), satisfies 0?x?1. The value of x is preferably in the range of 0.3 to 0.7. The average particle diameter of the powder determined from a TEM image is preferably 5 to 200 nm, more preferably 10 to 100 nm. The magnetic material has very high practical value because it enables the extremely high coercive force Hc of the ?-Fe2O3 crystal to be regulated to a level enabling utilization in magnetic recording medium and various other applications. The magnetic powder can be produced by a method combining the reverse micelle method and the sol-gel method.

Abstract: A magnetic material composed of ?-InxFe2-xO3 (wherein 0<x?0.30) crystal in which In is substituted for a portion of the Fe sites of the ?-Fe2O3 crystal. The crystal exhibits an X-ray diffraction pattern similar to that of an ?-Fe2O3 crystal structure and has the same space group as that of an ?-Fe2O3. The In content imparts to the magnetic material a magnetic phase transition temperature that is lower than that of the ?-Fe2O3 and a spin reorientation temperature that is higher than that of the ?-Fe2O3. The In content can also give the magnetic material a peak temperature of the imaginary part of the complex dielectric constant that is higher than that of the ?-Fe2O3.