Sm_2Fe_<17>N_3磁石の単磁区粒子と少数の磁区を有する粒子のエネルギー境界について

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The observation using magnetic force microscopy (MFM) of the Sm2Fe17N3 (SFN) particles having 2-4μm in diameters (D), totally about 15 particles, revealed that the particles show single-domain state and/or more than 3 domain state. Magnetic and domain wall energies of the single-domain particle (SDP) and these of two and three domain particles (2DP, 3DP) were calculated using the measured saturated polarization (Js) and the domain wall energy (γ). The results of the calculation are as follows : (1) the energy difference between the 2DP and 3DP is less than 6% in the total energies, in the range of ESDP > E3DP> E2DP : (2) the 3DP becomes stable, E2DP > E3DP, in the particles of D>3.0μm assuming the critical diameter is 2μm. Local demagnetizing field and existence of macroscopic defects in a particle strongly influence on the nucleation of domain wall formation, and it is obvious that the 2DP has a higher static magnetic energy compared to that of the 3DP. Therefore, it can be considered that the morphological complexity of the real particles results in the increase of stability of the 3DP than that of the 2DP in the sample particles. On the other hand, the discrepancy between the calculated critical diameter of SDP (dc≈0.18μm) and the measured one (dc≈2μm) can be explained by the temperature dependence of relative ratio of crystal magnetic anisotropy and saturated polarization in the SFN particles, i. e. (K=K(T) / KR. T.) vs. (Js= Js(T) / JsR. T.). It is revealed that the decrease in the anisotropy is pronounced in the higher temperature region near the Curie temperature than that in the saturated polarization (K1∝Jsn (n>4)). It should be the origin of the measured large SDP size than that of theoretically calculated critical radius using K1, and Js at room temperature.
社団法人電気学会の論文
2004-10-01

Sm_2Fe_<17>N_3磁石の単磁区粒子と少数の磁区を有する粒子のエネルギー境界について

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