Control of parameters in rare earth-transition metal alloys for magneto-optical recording media

Abstract

The techniques which can be used to control the magnetic and magneto-optical recording properties of sputtered amorphous thin films containing Fe,Co,Tb and Gd are reviewed. It is shown that by proper selection of composition one may independently vary the Curie temperature, the compensation temperature, and coercivity. On-the-other-hand it is shown that the uniaxial anisotropy perpendicular to the film plane and the magneto-optical Kerr rotation are dependent upon the substrate bias and argon pressure used during deposition. A procedure for optimizing the magnetic and magneto-optical properties of these materials for magneto-optical recording applications is outlined. Magneto-optic recording technology today employs amorphous thin films of rare earth-transition metal alloys. The films exhibit a preferred axis of magnetization perpendicular to the plane of the film. At room temperature the coercivity is high so the magnetization remains saturated perpendicular to the film plane, but at high temperatures (> 100°C) the coercivity is low, allowing the magnetization to reverse its direction in local submicrometer regions addressed by a focussed laser beam. To read out the recorded magnetization pattern, the kerr magneto-optic effect is used. This technology allows order of magnitude higher data densities than present rigid disk magnetic recording technology, freedom from head crashes, and removable media. The magnetization of the rare earth-transition metal thin films is determined by antiferromagnetic coupling between the rare earth and transition metal subnetwork magnetizations. Typically at low temperatures the rare earth magnetization dominates, whereas at high temperatures the transition metal magnetization is largest. At some intermediate temperature the two subnetwork magnetizations are equal and opposite resulting in zero net magnetization. At this so-called compensation temperature the coercivity tends toward infinity since there is no net magnetic moment to be acted upon by a magnetic field. At a sufficiently high temperature, the Curie temperature, the net magnetization and coercive force both tend toward zero. In this paper the factors which control the magnetic properties of sputtered GdTbFeCo amorphous films are discussed. Methods to independently control compensation point, Curie temperature, uniaxial anisotropy, and coercivity are explained.