Photon correlation spectroscopy with heterodyne mixing based on soft-x-ray magnetic circular dichroism

TL;DR

This paper introduces a heterodyne mixing technique in soft-x-ray magnetic circular dichroism to directly measure magnetic correlations, overcoming previous limitations of weak signals and inability to detect anticorrelations in magnetic XPCS.

Contribution

It proposes a novel heterodyne mixing method for magnetic XPCS that reconstructs the linear magnetic correlation function, enabling more accurate and broader magnetic fluctuation studies.

Findings

First-order magnetic correlation function can be reconstructed via heterodyne mixing.

The method enhances signal strength and allows detection of negative correlations.

Implementation with an absorption mask improves measurement stability.

Abstract

Many magnetic equilibrium states and phase transitions are characterized by fluctuations. Such magnetic fluctuation can in principle be detected with scattering-based x-ray photon correlation spectroscopy (XPCS). However, in the established approach of XPCS, the magnetic scattering signal is quadratic in the magnetic scattering cross section, which results not only in often prohibitively small signals but also in a fundamental inability to detect negative correlations (anticorrelations). Here, we propose to exploit the possibility of heterodyne mixing of the magnetic signal with static charge scattering to reconstruct the first-order (linear) magnetic correlation function. We show that the first-order magnetic scattering signal reconstructed from heterodyne scattering now directly represents the underlying magnetization texture. Moreover, we suggest a practical implementation based on an absorption mask rigidly connected to the sample, which not only produces a static charge scattering signal but also eliminates the problem of drift-induced artificial decay of the correlation functions. Our method thereby significantly broadens the range of scientific questions accessible by magnetic x-ray photon correlation spectroscopy.