High-Field Magnetization Process and Crystalline Electric Field Interaction in Rare-Earth Permanent-Magnet Materials

Abstract

AbstractDuring the last two decades the performance of permanent magnets has been greatly improved by introducing rare-earth (R) elements to their constituents [1]. It is doubtless that the high coercivity of these magnets comes from the large magnetic anisotropy originated by the crystalline electric field (CEF) acting on R ions with large orbital angular momentum. Magnetization measurements up to the high-field region, where the hard-axis magnetization saturates, are indispensable in order to obtain the basic insight into the magnetic anisotropy. Since 1985, we have been investigating systematically the high-field magnetization in a series of Nd2Fe14B-type compounds using mainly single crystal samples [2]. On the other hand, we have developed a method of analyzing these magnetization curves which consists of a simplified Hamiltonian taking the exchange and crystal field at the R ions into account, with the Fe sublattice being treated phenomenologically [3]. The essential feature in this model is the coupling of the two different types of sublattices. One is the R sublattice, which gives a large magnetic anisotropy owing to the CEF interaction. Another is the Fe sublattice, which determines the large magnetization and high Curie temperature as a result of strong Fe-Fe exchange interactions. This method has proven to be applicable not only to the R 2 M 14B system, with M = Fe or Co, but also to the pseudo-ternary system (R 1−x R′ x )2Fe14B [4] or other R-Fe-X systems such as R 2Fe17N x [5]. In these systems an interplay among the R-Fe exchange interaction, CEF potential acting on R ions and a large magnetic moment of the Fe sublattice leads to a variety of magnetic properties such as a first-order magnetization process (FOMP) and spin reorientation (SR) transitions. In general, such SR transitions will be accompanied by a considerable lattice deformation, since there is a large orbital contribution to the R magnetic moments, resulting in a strong coupling between the spin and lattice systems. It is therefore of interest to investigate the magnetoelastic properties of these materials.KeywordsMagnetization CurveSpin ReorientationSpin Reorientation TransitionCrystalline Electric FieldVolume MagnetostrictionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.