General theory of the coercive force due to domain wall pinning

Abstract

Due to the nonlinear nature of the relevant mathematical equations, previous solutions to the geometrically simple problem of pinning of a 180° ferromagnetic domain wall by a single planar defect in an infinite medium contain the approximation of small deviations in the nature of the defect material relative to the host matrix. We have enlarged the theory of such domain wall pinning to include all magnitudes of deviation of the magnetic anisotropy Ki , magnetization Mi , and/or magnetic exchange energy Ai , characterizing the defect for all defect widths. In particular, we have obtained graphs for the resultant reduced coercive force hc = HcM1/K1 , due to such domain wall pinning, as a function of the dimensionless constants F = A2M2/A1M1 and E = A2K2/A1K1 and of the defect width, as well as graphs for the maximum obtainable coercive force as a function of F and E. (Here i = 1 represents the host material and i = 2 the defect.) As an example, we discuss these results in terms of applications to the Sm2(Co,Cu,Zr,Fe)17 hard magnetic materials.

Effect of carbon on the coercivity and microstructure in fine-grained Nd–Fe–B sintered magnet

“…3 and 4. Therefore, the coercivity decrease due to the carbon contamination can be explained by the characteristics of the thin grain boundary phase, i.e., the increased carbon concentration causes the decrease of the Nd+Pr concentration in the grain boundary phase, resulting in a stronger intergranular exchange coupling [22]. Since the Nd+Pr concentration of the thin Nd-rich grain boundary phase is almost the same between the as-sintered low-C sample and post-sinter annealed high-C sample, Fig.…”

Isotropic, high coercive field in melt-spun tetragonal Heusler Mn3Ge

“…28 Inclusions and defects in hard magnetic materials might decrease the coercivity by serving as nucleation sites, or increase the coercivity by acting as pinning centers for domain walls. In this study, the large coercivity observed in Mn 74 Ge 26 and Mn 75 Ge 25 suggests that the κ-Mn 5 Ge 2 phase plays an important role in the coercivity enhancement as compared to single phase D0 22 Mn 76 Ge 24 and Mn 77 Ge 23 .…”

The study of negative thermal expansion and magnetic evolution in antiperovskite compounds Cu0.8-xSnxMn0.2NMn3(0 ≤ x ≤ 0.3)

“…Based on the essence of low-temperature meta-stable state, the larger H C at low temperature may be correlated with the pining of domain wall originating from magnetic frustration. 21 In addition, another interesting phenomenon can be found from Figs. 3(a), 3(b), and 3(c): around T L , the FC curve shows a discontinuous decrease for the sample x ¼ 0 while a discontinuous increase for the samples x Obviously, the value of DM FC =M FC decreases with increas-ing the magnetic field which is much contrary to the magnetic evolution for the sample x ¼ 0.…”