Systematic Research on High-Field Magnetization Process in Nd_2Fe_<14>B-type Mixed Compounds

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(1) High-field magnetization process in R_2Fe_<14>B single crystals (R : rare earth element) has been investigated experimentally and theoretically. A wide variety of magnetizations including the first-order magnetization process (FOMP) and the spin reorientation phenomena is reproduced by the following calculation : the ferromagnetism of the Fe sublattice is treated phenomenologically, and the crystalline electric field (CEF) theory is strictly applied to the R ions which are subject to the molecular field due to the Fe sublattice.(2) The magnetic behavior of single crystal Nd_2(Fe_<1-x>Al_x)_<14>B has been studied in steady high magnetic fields up to 300 kOe. The field H_j where the FOMP occurs increases rapidly with x. The experimental data are interpreted in terms of molecular field H_m which decreases with increasing x and the CEF parameters.(3) High-field magnetization measurements on single crystals of (Nd-Y)_2Fe_<14>B and (Nd-La)_2Fe_<14>B have been performed in steady high magnetic fields. The observed data including FOMP are successfully described by a simple dilution model based on CEF and molecular field parameters obtained for Nd_2Fe_<14>B.(4) In the quasi-binary system (Nd_<1-x>Dy_x)_2Fe_<14>B, the field H_j increases rapidly with x, reaching 320 kOe for the sample with x=0.33. The spin reorientation temperature, on the other hand, decreases with increasing x. These data are well explained by a simple a simple mixture model, in which the total free energy is the simple superposition of those of the two end members, neglecting the Nd-Dy interaction.(5) The high reproducibility of the present calculations enables us that the magnetic properties of the quasi-binary system (R_<1-x>R'_x)_2Fe_<14>B can be predicted for any combination of rare earth elements R and R'.