First-principles calculations of magnetic properties for analysis of magnetization processes in rare-earth permanent magnets. Issue 1 (31st December 2021)

• Record Type: Journal Article
• Authors: Tsuchiura, Hiroki; Yoshioka, Takuya; Novák, Pavel; Fischbacher, Johann; Kovacs, Alexander; Schrefl, Thomas
• Is Part Of: Science and technology of advanced materials. Volume 22:Issue 1(2021)
• Page Start: 748
• Page End: 757
• Publication Date: 2021-12-31
• Subjects: Rare-earth permanent magnets -- crystal field theory -- first-principles calculations -- atomistic spin model -- micromagnetic simulations; 40 Optical, magnetic and electronic device materials -- 106 Metallic materials; 401 1st principles methods -- 404 Dynamics simulations -- 406 Multi-scale / multi-physics modelling; Materials -- Technological innovations -- Periodicals; 620.112
• DOI: 10.1080/14686996.2021.1947119
• Languages: English
• ISSNs: 1468-6996

Abstract

ABSTRACT: It has been empirically known that the coercivity of rare-earth permanent magnets depends on the size and shape of fine particles of the main phase in the system. Also, recent experimental observations have suggested that the atomic-scale structures around the grain-boundaries of the fine particles play a crucial role to determine their switching fields. In this article, we review a theoretical attempt to describe the finite temperature magnetic properties and to evaluate the reduction of the switching fields of fine particles of several rare-earth permanent magnetic materials based on an atomistic spin model that is constructed using first-principles calculations. It is shown that, over a wide temperature range, the spin model gives a good description of the magnetization curves of rare-earth intermetallic compounds such as R 2 Fe14 B ( R = Dy, Ho, Pr, Nd, Sm) and SmFe12 . The atomistic spin model approach is also used to describe the local magnetic anisotropy around the surfaces of the fine particles, and predicts that the rare-earth ions may exhibit planar magnetic anisotropy when they are on the crystalline-structure surfaces of the particles. The dynamical simulation of the atomistic spin model and the corresponding micromagnetic simulation show that the planar surface magnetic anisotropy causes a reduction in the switching field of fine particles by approximately 20–30%, which may be relevant to the atomic-scale surface effects found in the experimental studies. Graphical abstract: uf0001