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Calculating temperature-dependent properties of Nd2Fe14 B permanent magnets by atomistic spin model simulations

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JournalPhysical Review B
DateAccepted/In press - 30 May 2019
DatePublished (current) - 6 Jun 2019
Issue number21
Volume99
Number of pages11
Original languageEnglish

Abstract

Temperature-dependent magnetic properties of Nd2Fe14B permanent magnets, i.e., saturation magnetization Ms(T), effective magnetic anisotropy constants Kieff(T)(i=1,2,3), domain-wall width δw(T), and exchange stiffness constant Ae(T), are calculated by using ab initio informed atomistic spin model simulations. We construct the atomistic spin model Hamiltonian for Nd2Fe14B by using the Heisenberg exchange of Fe-Fe and Fe-Nd atomic pairs, the uniaxial single-ion anisotropy of Fe atoms, and the crystal-field energy of Nd ions, which is approximately expanded into an energy formula featured by second-, fourth-, and sixth-order phenomenological anisotropy constants. After applying a temperature rescaling strategy, we show that the calculated Curie temperature, spin-reorientation phenomenon, Ms(T),δw(T), and Kieff(T), agree well with the experimental results. Ae(T) is estimated through a general continuum description of the domain-wall profile by mapping atomistic magnetic moments to the macroscopic magnetization. Ae is found to decrease more slowly than K1eff with increasing temperature and approximately scale with normalized magnetization as Ae(T)∼m1.2. Specifically, the possible domain-wall configurations at temperatures below the spin-reorientation temperature and the associated δw and Ae are identified. This work provokes a scale bridge between ab initio calculations and temperature-dependent micromagnetic simulations of Nd-Fe-B permanent magnets.

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