High-resolution resonant inelastic soft X-ray scattering as a probe of the crystal electrical field in lanthanides demonstrated for the case of CeRh2Si2

TL;DR

This paper demonstrates that high-resolution resonant inelastic soft X-ray scattering (RIXS) can effectively probe crystal electric field (CEF) excitations in lanthanides, offering advantages over traditional inelastic neutron scattering, exemplified by the study of CeRh2Si2.

Contribution

The study introduces high-resolution RIXS with polarization analysis as a new method for determining CEF schemes in lanthanides, providing a viable alternative to INS.

Findings

RIXS can determine CEF schemes consistent with INS and susceptibility data.

High energy resolution (~30 meV) enhances RIXS effectiveness.

RIXS is suitable for small samples and has high cross sections for lanthanides.

Abstract

The magnetic properties of rare earth compounds are usually well captured by assuming a fully localized f shell and only considering the Hund's rule ground state multiplet split by a crystal electrical field (CEF). Currently, the standard technique for probing CEF excitations in lanthanides is inelastic neutron scattering. Here we show that with the recent leap in energy resolution, resonant inelastic soft X-ray scattering has become a serious alternative for looking at CEF excitations with some distinct advantages compared to INS. As an example we study the CEF scheme in CeRh2Si2, a system that has been intensely studied for more than two decades now but for which no consensus has been reached yet as to its CEF scheme. We used two new features that have only become available very recently in RIXS, high energy resolution of about 30 meV as well as polarization analysis in the scattered beam, to find a unique CEF description for CeRh2Si2. The result agrees well with previous INS and magnetic susceptibility measurements. Due to its strong resonant character, RIXS is applicable to very small samples, presents very high cross sections for all lanthanides, and further benefits from the very weak coupling to phonon excitation. The rapid progress in energy resolution of RIXS spectrometers is making this technique increasingly attractive for the investigation of the CEF scheme in lanthanides.