Micromagnetic simulations of reversal magnetization in cerium-containing magnets

Single-grain models with different cerium contents or structural parameters have been introduced to investigate the reversal magnetization behaviors in cerium-containing magnets. All the micromagnetic simulations are carried out via the object oriented micromagnetic framework (OOMMF). As for single (Nd,Ce)₂Fe₁₄B type grain, the coercivity decreases monotonously with the increase of the cerium content. Four types of grain structure have been compared:single (Nd,Ce)₂Fe₁₄B type, core ((Nd,Ce)₂Fe₁₄B)-shell (Nd₂Fe₁₄B) type with 2 nm thick shell, core (Ce₂Fe₁₄B)-shell (Nd₂Fe₁₄B) type, and core (Nd₂Fe₁₄B)-shell (Ce₂Fe₁₄B) type. It is found that core ((Nd,Ce)₂Fe₁₄B)-shell (Nd₂Fe₁₄B) type grain with 2 nm thick shell always presents the largest coercivity under the same total cerium content. Furthermore, the relationship between the coercivity and the shell thickness t in core ((Nd,Ce)₂Fe₁₄B)-shell (Nd₂Fe₁₄B) type grain has been studied. When the total cerium content is kept at 20.51 at.%, the analyzed results show that as t varies from 1 nm to 7 nm, the coercivity gradually ascends at the beginning, then quickly descends after reaching the maximum value when t=5 nm. From the perspective of the positions of nucleation points, the reasons why t affects the coercivity are discussed in detail.