Coercivity Mechanism of Ga-Doped Nd-Fe-B Sintered Magnets

Abstract

The alignment dependence and angular dependence of coercivity (ALDC and ANDC, respectively) of aligned and isotropically aligned Ga-doped Nd 14.79 Ga 0.57 B 5,24 Co 1.11 Fe bal sintered magnets were analyzed, and the results were compared with those of ferrite magnets, which were reported in our previous paper. The coercivity of Ga-doped Nd-Fe-B magnets decreases as alignment improves. The ALDC of this magnet is similar to that of ferrite magnets. The angle of the magnetization-reversal area (AMRA) of the aligned Ga-doped magnets has at coercivity an angular tilt of 41.4 • , which is wider than that of the ferrite magnets. The ANDC of Ga-doped Nd-Fe-B sintered magnets displays similar behavior with that of ferrite magnets but is slightly lower than that of ferrite magnets, which is expected from AMRA of Ga-doped Nd-Fe-B sintered magnets. These results support our proposed coercivity mechanism; specifically, the magnetic domain walls are pinned at grains with tilted easy magnetization directions or c-axis tilted from the easy magnetization of the magnet. When the magnetic domain walls are de-pinned from the pinning sites, they jump through several grains, thereby determining the coercivity.

Alignment and Angular Dependences of Coercivity for (Sm, Ce)₂(Co, Fe, Cu, Zr)₁₇ Magnets

“…The ANDC of the Sm 0.67 Ce 0.33 (Co 0.73 Fe 0.2 Cu 0.05 Zr 0.02 ) 7.2 magnet only appears similar to the magnetization behavior obtained from the StonerWohlfarth or the coherent rotation model, to which the behavior of Ga-doped NdFeB sintered magnets and SrO•6Fe 2 O 3 is also similar. 25,28) Finally, for angles up to 50°, the ANDC of isotropically aligned magnets agrees well with the calculation results. This result holds for NdFeB sintered magnets, Ga-doped Nd FeB sintered magnets, and ferrite magnets.…”

“…The H cJ of these magnets decreases from 0°to 40°and increases thereafter, the trend being similar to that of ferrite magnets and Ga-doped NdFeB sintered magnets. 25,28) The ANDC of these magnets appears similar to that obtained from the StonerWohlfarth model. We explained the ANDC of ferrite magnets and Ga-doped Nd FeB magnets as arising from the motion of magnetic domain walls if the results from the ALDC of these magnets are used.…”

“…We explained the ANDC of ferrite magnets and Ga-doped Nd FeB magnets as arising from the motion of magnetic domain walls if the results from the ALDC of these magnets are used. 25,28) For Sm 0.67 Ce 0.33 (Co 0.73 Fe 0.2 Cu 0.05 Zr 0.02 ) 7.2 magnets, the ANDC and the ALDC do not exhibit the correlation observed in NdFeB magnets and ferrite magnets and, at first glance, the ANDC appears identical to that from the StonerWohlfarth model. Nevertheless, without doubt, the H cJ of Sm 2 Co 17 -type magnets is determined by this domain wall motion.…”

“…26) The ANDC of these magnets agrees well with these calculations, which are obtained assuming that each grain undergoes an independent magnetic reversal through the motion of the magnetic domain walls for angles up to 50°and is similar to those of NdFeB sintered magnets, Ga-doped NdFeB sintered magnets, and ferrite magnets. 25,26,28) The ANDC of isotropically oriented magnets also suggests that the motion of the magnetic domain wall determines the coercivity.…”

“…1009 to 1012 © 2021 The Japan Institute of Metals and Materials magnetic domain walls even though the ANDC manifests as a coherent rotation. 25,28) In determining their coercivity mechanism, we remarked that the ANDC does not suffice; both ALDC and ANDC need to be examined for this determination.…”