First-principles study on interface magnetic structure in Nd${}_2$Fe${}_{14}$B/(Fe,Co) exchange spring magnets

TL;DR

This study uses first-principles calculations to explore how different interface structures in Nd2Fe14B/(Fe,Co) multilayers affect magnetic coupling and magnetization, revealing conditions for enhanced or degraded magnetic properties.

Contribution

It provides detailed insights into the interface magnetic structures and coupling mechanisms in Nd2Fe14B/(Fe,Co) systems, highlighting the impact of crystallographic alignment and interlayer distances.

Findings

Improved remanent magnetization in certain NFB/Fe and NFB/Co configurations.

Remanence degradation due to anti-parallel alignment in NFB(100)/Fe.

Anti-ferromagnetic coupling at the interface with short interlayer distance.

Abstract

The magnetic properties of Nd${}_2$Fe${}_{14}$B (NFB)/transition metal (TM = Fe, Co) multilayer systems are studied on the basis of first-principles density functional calculations. We optimize the model structure under a variety of crystallographic alignments of the NFB layer, and analyze the mechanism of interface magnetic coupling. Improvements in remanent magnetization compared to that of single NFB are observed in NFB(001)/Fe, NFB(110)/Fe, and NFB(100)/Co. On the other hand, in NFB(100)/Fe, remanence degradation due to the anti-parallel magnetization alignment between NFB and Fe layers is observed. In this system, which has the shortest optimized interlayer distance among all considered systems, an itinerant electron magnetism is required around the interface to lower the total energy, and accordingly, anti-ferromagnetic coupling is preferred. The significant difference in property between NFB(100)/Fe and NFB(100)/Co is attributed to the difference between their interface structures, optimized interlayer distances, and magnetic stiffness of TM layers.