Chiral Spin Bobbers in Exchange-Coupled Hard-Soft Magnetic Bilayers

TL;DR

This paper reports the discovery of chiral spin bobbers in exchange-coupled MnBi:Co-Fe bilayers, revealing a new skyrmionic spin structure with potential implications for magnetic materials and spintronics.

Contribution

It introduces a novel chiral spin bobber structure in hard-soft magnetic bilayers, combining experimental and simulation evidence.

Findings

Identification of curling-type magnetization reversal

Observation of a new skyrmionic spin structure

Relevance for permanent magnets and spintronics

Abstract

The spin structure of exchange-coupled MnBi:Co-Fe bilayers is investigated by X-ray magnetic circular dichroism (XMCD), polarized neutron reflectometry (PNR), and micromagnetic simu-lations. The purpose of the present research is two-fold. First, the current search for new permanent-magnet materials includes hard-soft nanocomposites, and the analysis of coercivity mechanisms in these structures is an important aspect of this quest. Second, topological micro-magnetic structures such as skyrmions have recently become of intense fundamental and applied research, for example in the context of spin-based electronics. We find that the magnetization reversal of the MnBi:Co-Fe bilayer structure involves a curling-type twisting of the magnetization in the film plane. This curling in the exchange-coupled hard-soft magnetic bilayers is reminiscent of chiral spin structures known as bobbers and, in fact, establishes a new type of skyrmionic spin structure.