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.
Highlights
When a rare-earth ion is placed in a crystalline environment, spherical symmetry is broken and its electronic levels are modified with respect to those of the free atom
We have recently shown that these excitations can in principle be seen with RIXS at the M4,5 edges of the lanthanides [4] but the available energy resolution of 100 meV and more was not sufficient for resolving the crystal electric field (CEF) splittings in rare earth ions
Our results show that RIXS could become a valuable alternative for CEF studies of rare-earth ions with some distinct advantages and disadvantages that make it very complementary to INS
Summary
When a rare-earth ion is placed in a crystalline environment, spherical symmetry is broken and its electronic levels are modified with respect to those of the free atom. The most modern RIXS spectrometers today can achieve an energy resolution of a few tens of meV at 1 keV incident photon energy, offer the possibility of truly three-dimensional mapping in q space, and allow for polarization analysis in the scattered beam This opens new perspectives for studying the low energy excitations in strongly correlated systems at energy scales relevant for the material properties. Recent examples that showcase these new possibilities are the work on orbital, spin, and chargedensity wave excitations in cuprates and other transition metal oxides [5,6,7,8,9,10,11] This high-resolution RIXS work has focused on strongly correlated, transition metal compounds.
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