Quantitative magnetic-moment mapping of a permanent-magnet material by X-ray magnetic circular dichroism nano-spectroscopy

Tetsuro Ueno,Ai Hashimoto,Kanta Ono,Yasuo Takeichi

doi:10.1063/1.4975043

Abstract

We demonstrate the quantitative mapping of magnetic moments in a permanent-magnet material by X-ray magnetic circular dichroism nano-spectroscopy. An SmCo5 specimen was prepared from the bulk material by using a micro-fabrication technique. Scanning transmission X-ray microscopy images were obtained around the Sm M4,5 absorption edges. By applying the magneto-optical sum rules to these images, we obtained quantitative maps of the orbital and spin magnetic moments as well as their ratio. We found that the magnitudes of the orbital and spin magnetic moments and their ratio do not depend on thickness of the specimen.

Highlights

Recent progress in X-ray microscopy has enabled us to visualize microstructures in magnetic materials such as magnetic domains.[1]
Magnetic domains have been observed using several techniques such as photoemission electron microscopy (PEEM),[2] full-field transmission X-ray microscopy (TXM),[3,4] and X-ray ptychography,[5,6] for thin films and multilayers artificially fabricated on membranes
A spatial resolution of approximately 10 nm can be achieved using ptychography owing to the high coherence of synchrotron radiation X-rays.[5]. The microstructures such as crystallinity, grain size, and grain boundaries of actual permanent magnet materials are known to be different from those of films, and the magnetic domain imaging of bulk permanent magnet materials has rarely been reported, except for a study on the scanning transmission X-ray microscopy (STXM) of Nd–Fe–B magnets.[7]. These imaging techniques are based on X-ray magnetic circular dichroism (XMCD), a magneto-optical effect in core absorption that is induced by circularly polarized X-rays.[8]

Summary

Introduction

Recent progress in X-ray microscopy has enabled us to visualize microstructures in magnetic materials such as magnetic domains.[1]. A spatial resolution of approximately 10 nm can be achieved using ptychography owing to the high coherence of synchrotron radiation X-rays.[5] the microstructures such as crystallinity, grain size, and grain boundaries of actual permanent magnet materials are known to be different from those of films, and the magnetic domain imaging of bulk permanent magnet materials has rarely been reported, except for a study on the scanning transmission X-ray microscopy (STXM) of Nd–Fe–B magnets.[7] These imaging techniques are based on X-ray magnetic circular dichroism (XMCD), a magneto-optical effect in core absorption that is induced by circularly polarized X-rays.[8] XMCD spectroscopy is known to be a powerful experimental technique to probe the magnetic properties of materials.[9,10] As a unique characteristic of XMCD spectroscopy, the orbital and spin magnetic moments can be separately evaluated for specific elements by using the magneto-optical sum rules.[11,12,13] In this context, XMCD nano-spectroscopy can be performed using X-ray microscopes to investigate magnetic moments at very specific areas of materials. Robertson et al reported the spatial distribution of the orbital-to-spin magnetic-moment ratio in the vicinity of magnetic domain walls of a Co/Pt multilayer.[3]

Methods

Results

Conclusion