Three- and two-dimensional calculations for the interface anisotropy dependence of magnetic properties of exchange-spring Nd₂Fe₁₄B/α-Fe multilayers with out-of-plane easy axes*

Abstract

Hysteresis loops, energy products and magnetic moment distributions of perpendicularly oriented Nd2Fe14B/α-Fe exchange-spring multilayers are studied systematically based on both three-dimensional (3D) and one-dimensional (1D) micromagnetic methods, focused on the influence of the interface anisotropy. The calculated results are carefully compared with each other. The interface anisotropy effect is very palpable on the nucleation, pinning and coercive fields when the soft layer is very thin. However, as the soft layer thickness increases, the pinning and coercive fields are almost unchanged with the increment of interface anisotropy though the nucleation field still monotonically rises. Negative interface anisotropy decreases the maximum energy products and increases slightly the angles between the magnetization and applied field. The magnetic moment distributions in the thickness direction at various applied fields demonstrate a progress of three-step magnetic reversal, i.e., nucleation, evolution and irreversible motion of the domain wall. The above results calculated by two models are in good agreement with each other. Moreover, the in-plane magnetic moment orientations based on two models are different. The 3D calculation shows a progress of generation and disappearance of vortex state, however, the magnetization orientations within the film plane calculated by the 1D model are coherent. Simulation results suggest that negative interface anisotropy is necessarily avoided experimentally.

Micromagnetic study of magnetization reversal in inhomogeneous permanent magnets

“…[18] Instead, micromagnetic simulation provides an important way to reveal the magnetization dynamics in permanent magnets. [23][24][25] Up to date, micromagnetic simulations [26][27][28][29] have been widely used to study the magnetization phenomena on the intermediate scale between the quantum mechanical scale of individual atoms and the macroscale, such as the dynamic response of a micromagnetic system and the characterization of 3D magnetization distribution. [9,30] By employing large-scale micromagnetic simulations, the effects of grain size, [31] grain shape, [32] and grain boundary phase [33] on the coercivity of Nd-Fe-B permanent magnets were well investigated.…”

Magnetic anisotropy in 5d transition metal–porphyrin molecules*

“…To compromise this contradiction, different approaches such as strain and electric field have been proposed to manipulate the MAE in writing information. [23][24][25][26][27] In this paper, we investigate the electronic and magnetic properties of 5d TM-P molecules and the manipulation of MAE for iridium-porphyrin-based (Ir-P) SMM by biaxial tensile strain based on the first-principles calculations. We find that W-P, Re-P, Os-P, and Ir-P possess the considerable MAE and the magnitude of MAE can be manipulated by the biaxial tensile strain.…”