Highly Oriented Magnetic Film Composed of Ga-Substituted ε-Iron Oxide and the Angular Dependence of the Magnetic Hysteresis Loops

We report a magnetic film based on crystallographically oriented metal-substituted epsilon-iron oxide, epsilon-Ga0.45Fe1.55O3. This film was prepared by mixing nanoparticles and a vehicle resin under an applied external magnetic field. The a-axis of the orthorhombic crystal structure with a Pna2(1) space group is oriented out of the plane of the film. The degree of orientation is very high with a Lotgering factor of 0.94. The angular dependence of the magnetic hysteresis loops at room temperature shows a rectangular hysteresis loop with a coercive field of 9.7 kOe and a magnetization of 30.4 emug(-1) at 7 T (tesla) when the external field is along the out-of-plane direction with respect to the plane of the film, indicating that the easy axis corresponds to the crystallographic a-axis. To understand the origin of the high degree of orientation, we calculated the magnitude of the magnetic coupling between the epsilon-Ga0.45Fe1.55O3 magnetic nanoparticles based on the magnetic dipole-dipole interaction. The theoretical model considering uniaxial magnetic anisotropy reproduces the angular dependence of the magnetic loops well.