Magnetic anisotropy energy in single crystal Y1.8Er0.2Fe14B (invited) (abstract)

Abstract

There has been considerable interest in tetragonal R2Fe14B compounds as a basis for a new class of permanent magnet materials because of the unusually large energy products they exhibit at room temperature for certain rare-earth substitutions. The origin of the high-energy products is directly related to the large saturation magnetization and magnetic anisotropy energy. The magnetocrystalline anisotropy energy is believed to be directly related to an interaction between the 4f-electrons and the crystal field: however, to date few if any direct comparisons have been made between the experimental magnetic anisotropy and crystal field theory. The reason being that the large anisotropy energy makes it very difficult to use conventional torque magnetometry techniques to determine the angular dependence of the magnetic free energy, particularly at low temperatures where the higher-order terms become important. In this investigation we determine the angular dependence of the magnetic free energy as a function of temperature for Y1.8Er0.2Fe14B using high field (6 T) torque magnetometry techniques and make a direct comparison of the free energy with the energy calculated using a model based on crystal field theory. Y1.8Er0.2Fe14B was chosen because the Fe and Er sublattice anisotropy energies nearly cancel at low temperatures making it possible to measure anisotropy. Excellent agreement was obtained between the model and experiment.