Experimental determination of the saturation polarization and the anisotropy field in ThMn₁₂-type magnets using the LAFS method

The law of approach to ferromagnetic saturation (LAFS) method is required for the accurate measurement of the magnetic properties of magnetically isotropic materials. In this study, we examined the accuracy of the following two LAFS methods for determining the saturation polarization (J_s) and anisotropy field (H_a) of isotropic magnets: (1) the method based on the relationship between polarization (J) and applied field (H; 1/H²); and (2) the method based on the relationship between susceptibility (dJ/dH) and 1/H³. We used an isotropic magnet prepared from a commercial ferrite magnet powder with well-known magnetic properties and low H_a as a standard magnet for evaluating the two LAFS methods. Then, we measured the J_s and H_a values of our -Ti_0.7 compounds with a ThMn₁₂ structure, (Nd_0.8Zr_0.2)(Fe_0.9Co_0.1)_11.3Ti_0.7N_1.5 and (Sm_0.9Zr_0.1)(Fe_0.8Co_0.2)_11.3Ti_0.7, including in the high-temperature region (>373 K), where the reduction of H_a was observed. Finding the adequate maximum magnetic fields, where the J_s and H_a values obtained by the two LAFS methods agree well, is important for the proper application of the method to isotropic magnet samples. The results of the LAFS methods revealed that the J_s values of the new compounds are similar at RT, but higher than that of the Nd₂Fe₁₄B phase in the high-temperature region. Because the -Ti_0.7 compounds are almost α-(Fe,Co)-phase-free, their H_a values are also higher than that of Nd₂Fe₁₄B over the whole temperature region.