TY - JOUR
T1 - Role of atomic-scale thermal fluctuations in the coercivity
AU - Toga, Yuta
AU - Miyashita, Seiji
AU - Sakuma, Akimasa
AU - Miyake, Takashi
N1 - Funding Information:
We acknowledge fruitful discussions with Satoshi Okamoto, Munetaka Sasaki, Masamichi Nishino, Taichi Hinokihara, and Satoshi Hirosawa. This work is partially supported by ESICMM, Grant Number JPMXP0112101004, through MEXT; by MEXT as a social and scientific priority issue (CDMSI) to be tackled by using a post-K computer. The computation was performed on Supercomputers at NIMS; ISSP, University of Tokyo; ACCMS, Kyoto University; RIIT, Kyushu University.
Publisher Copyright:
© 2020, The Author(s).
PY - 2020/12/1
Y1 - 2020/12/1
N2 - The microscopic mechanism of coercivity at finite temperature is a crucial issue for permanent magnets. Here we present the temperature dependence of the coercivity of an atomistic spin model for the highest-performance magnet Nd2Fe14B. For quantitative analysis of the magnetization reversal with thermal fluctuations, we focus on the free energy landscape as a function of the magnetization. The free energy is calculated by the replica-exchange Wang–Landau method. This approach allows us to address a slow nucleation problem, i.e., thermal activation effects, in the magnetization reversal. We concretely observed that the thermal fluctuations lead to a downward convexity in the coercivity concerning the temperature. Additionally, through analyzing the microscopic process of the thermal activation (nucleation), we discover the activation volume is insensitive to a magnetic field around the coercivity. The insensitivity explains the linear reduction of the free energy barrier by the magnetic field in the nucleation process.
AB - The microscopic mechanism of coercivity at finite temperature is a crucial issue for permanent magnets. Here we present the temperature dependence of the coercivity of an atomistic spin model for the highest-performance magnet Nd2Fe14B. For quantitative analysis of the magnetization reversal with thermal fluctuations, we focus on the free energy landscape as a function of the magnetization. The free energy is calculated by the replica-exchange Wang–Landau method. This approach allows us to address a slow nucleation problem, i.e., thermal activation effects, in the magnetization reversal. We concretely observed that the thermal fluctuations lead to a downward convexity in the coercivity concerning the temperature. Additionally, through analyzing the microscopic process of the thermal activation (nucleation), we discover the activation volume is insensitive to a magnetic field around the coercivity. The insensitivity explains the linear reduction of the free energy barrier by the magnetic field in the nucleation process.
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U2 - 10.1038/s41524-020-0325-6
DO - 10.1038/s41524-020-0325-6
M3 - Article
AN - SCOPUS:85085843512
SN - 2057-3960
VL - 6
JO - npj Computational Materials
JF - npj Computational Materials
IS - 1
M1 - 67
ER -