The magnetic properties of amorphous and nanocrystalline cobalt-rare earth films.

摘要

Magnetic materials are of great technological importance for their use in transformers, electric motors, computer disks and hard drives, etc. Understanding the intrinsic physical properties of magnetic materials is essential in order to develop new and better materials for these applications. Presented here is a study of the magnetic properties of amorphous and nanocrystalline cobalt-rare earth (Co-R, where R = Y, Pr, Gd, and Dy) films composed of very small crystalline grains, about 2–200 nm in size. The films are produced by co-sputtering two single element targets onto a single substrate. Many are then annealed briefly to produce magnetic films composed of nanoscale crystallites. The magnetic properties of these films depend largely on the relative strengths of the exchange interaction, which tends to align the spins within a group of crystallites, and the magnetocrystalline anisotropy, which tends to align the spins within each crystallite to an easy direction defined by the crystal lattice. The ratio of these two competing interactions varies strongly with grain size as predicted by the random magnetic anisotropy model. The coercivity, remanent magnetization, initial magnetization, etc., are discussed in light of the predictions made by the models of Callen et al (1977), Chi and Alben (1977), Chudnovsky (1986), and Fukunaga and Inoue (1992).