Magneto-optic effect and perpendicular magnetic anisotropy are investigated in thermally evaporated amorphous TbFeCo magnetic thin film which is a promising erasable, high density magneto-optic recording material. For the measurement of small rotation angle, polarization modulation using Faraday rotator and phase sensitive detection techniques are used. The measured Kerr hysteresis loops show good squareness and large coercivity which is desirable magnetic properties that magneto-optic recording material must have. The magneto-optic properties of the TbFeCo thin film degrade significantly with aging time in air at room temperature, particularly in the coercivity and remanent Kerr rotation angle which is explained by the oxidation of mainly Tb atom in the alloy due to the larger oxygen affinity of Tb than those of Fe and Co.
In order to clarify the origin of the perpendicular magnetic anisotropy, the effects of deposition angle on Kerr hysteresis loop, perpendicular anisotropy constant and internal stress are investigated.
The measurements of Kerr hysteresis loops in the polar and longitudinal directions show that, as the deposition angle increases, the polar Kerr hysteresis loop deteriorates, while the longitudinal Kerr hysteresis loop becomes prominent.
The perpendicular anisotropy constant is positive and its magnitude is $8×10^5 erg$/㎤ at normal incidence deposition. As the deposition angle increases, the perpendicular anisotropy constant decreases. It is positive at deposition angle smaller than 30˚, while it becomes negative for larger deposition angle than 30˚. Namely, the easy direction of magnetization shifts from the film normal direction to the in-plane direction.
The measurement of internal planar stress, which is due to the substrate constraint, reveals that the stress is compressive for deposition angle smaller than 30˚, while it is tensile for larger deposition angle than 30˚. The internal stress and the perpendicular anisotropy constant change their polarities at the same deposition angle of 30˚, which means that the perpendicular anisotropy can exist only when the internal stress is compressive in the plane of the film. The magnitude of the stress-induced anisotropy constant shows that the internal compressive stress contributes dominantly to the perpendicular anisotropy.
And the deterioration of the polar Kerr hysteresis loop with deposition angle is explaned from the change of the perpendicular anisotropy constant. Further, the normal incidence deposition is essential to obtain thin films with large perpendicular anisotropy constant and square hysteresis loop.
