Anisotropy of exchange stiffness based on atomic-scale magnetic properties in the rare-earth permanent magnetNd2Fe14B

Abstract

We examine the anisotropic properties of the exchange stiffness constant, A, for rare-earth permanent magnet, Nd2Fe14B, by connecting analyses with two different scales of length, i.e., Monte Carlo (MC) method with an atomistic spin model and Landau-Lifshitz-Gilbert (LLG) equation with a continuous magnetic model. The atomistic MC simulations are performed on the spin model of Nd2Fe14B constructed from ab-initio calculations, and the LLG micromagnetics simulations are performed with the parameters obtained by the MC simulations. We clarify that the amplitude and the thermal property of A depend on the orientation in the crystal, which are attributed to the layered structure of Nd atoms and weak exchange couplings between Nd and Fe atoms. We also confirm that the anisotropy of A significantly affects the threshold field for the magnetization reversal (coercivity) given by the depinning process.

First-principles Study of Spin-Wave Dispersion in Sm(FeCo)12

“…Figure C.6 shows the D a /D c ratio for bcc Fe, fcc Co, and fcc Ni with the tetragonal deformation. The D a /D c ratio in Fe and Ni tend to have a negative correlation with c/a, which is opposite to the cases of SmFe 12 (this work) and Nd 2 Fe 14 B [17]. In contrast, fcc Co has a positive correlation to c/a.…”

“…(3). Toga et al [17] has recently reported the values of the exchange stiffness at finite temperatures in their Monte Carlo simulation for Nd 2 Fe 14 B, which is also an Fe-rich rare-earth compound. Though they did not present the value at zero temperature, the order of the exchange stiffness seem to agree with our results for SmFe 12 .…”

Anisotropic exchange in Nd–Fe–B permanent magnets

“…The temperature-dependent A e of Nd 2 Fe 14 B is evaluated through ASM simulation by using VAMPIRE [36] based on the atomistic spin Hamiltonian which is proposed and parameterized previously [37][38][39][40][41]. Detailed formulations for the ASM of Nd 2 Fe 14 B are provided in the Supplemental Material.…”

First-principles calculations of the magnetocrystalline anisotropy of the prototype 2:17 cell boundary phaseYCo1-x-yFePatrick1, Matsumoto2, Staunton3 2019Journal of Magnetism and Magnetic Materials132181View full textAdd to dashboardCite

“…We have not yet established a formal framework to extract the exchange stiffness constant A m from the DFT-DLM calculations. A similar challenge is encountered when performing calculations based on atomistic spin models [45].…”