Atomistic theory of thermally activated magnetization processes in Nd2Fe14B permanent magnet

Seiji Miyashita, Masamichi Nishino, Yuta Toga, Taichi Hinokihara, Ismail Enes Uysal, Takashi Miyake, Hisazumi Akai, Satoshi Hirosawa, Akimasa Sakuma

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

Abstract

To study the temperature dependence of magnetic properties of permanent magnets, methods of treating the thermal fluctuation causing the thermal activation phenomena must be established. To study finite-temperature properties quantitatively, we need atomistic energy information to calculate the canonical distribution. In the present review, we report our recent studies on the thermal properties of the Nd2Fe14B magnet and the methods of studying them. We first propose an atomistic Hamiltonian and show various thermodynamic properties, for example, the temperature dependences of the magnetization showing a spin reorientation transition, the magnetic anisotropy energy, the domain wall profiles, the anisotropy of the exchange stiffness constant, and the spectrum of ferromagnetic resonance. The effects of the dipole–dipole interaction (DDI) in large grains are also presented. In addition to these equilibrium properties, the temperature dependence of the coercivity of a single grain was studied using the stochastic Landau-Lifshitz-Gilbert equation and also by the analysis of the free energy landscape, which was obtained by Monte Carlo simulation. The upper limit of coercivity at room temperature was found to be about 3 T at room temperature. The coercivity of a polycrystalline magnet, that is, an ensemble of interactinve grains, is expected to be reduced further by the effects of the grain boundary phase, which is also studied. Surface nucleation is a key ingredient in the domain wall depinning process. Finally, we study the effect of DDI among grains and also discuss the distribution of properties of grains from the viewpoint of first-order reversal curve.

Original languageEnglish
Pages (from-to)658-682
Number of pages25
JournalScience and Technology of Advanced Materials
Volume22
Issue number1
DOIs
Publication statusPublished - 2021

Keywords

  • 40 Optical, magnetic and electronic device materials; 203 Magnetics / Spintronics / Superconductors; 400 Modeling/Simulations
  • Coercivity
  • dipole–dipole interaction
  • finite temperature
  • Monte Carlo method
  • stochastic LLG equation
  • thermal fluctuation

ASJC Scopus subject areas

  • Materials Science(all)

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