Soft X‐Ray Magnetic Circular Dichroism of Vanadium in the Metal–Insulator Two‐Phase Region of Paramagnetic V2O3 Doped with 1.1% Chromium

Detlef Schmitz,Olle Eriksson,Sergey Ivanov,Chen Luo,Konrad Siemensmeyer,Silke Biermann,Florin Radu,Sumanta Bhandary,Hanjo Ryll,Heiko Wende,Carolin Schmitz-Antoniak

doi:10.1002/pssb.201900456

Abstract

V2O3 doped with 1.1% Cr is investigated at its isostructural correlation‐driven metal–insulator transition near room temperature in its paramagnetic state with X‐ray magnetic circular dichroism (XMCD) spectroscopy in external magnetic fields. A relative XMCD amplitude of about 2 permille is observed at the L2,3 absorption edges of vanadium as expected for magnetic moment per mass values of the order of 1 J T−1 kg−1 from magnetometry and the literature. Across the metal–insulator transition, the vanadium XMCD spectral shape significantly changes. According to atomic multiplet simulations, these changes are due to a changing orbital occupation indicating a changing phase composition. According to estimates used in this study, the dipole moment of the spin density distribution in the bulk increases such that the effective vanadium spin moment increases by a few percent with temperature in the two‐phase region. Thereby, it partially compensates for the decrease in the relative XMCD amplitude due to a decreasing alignment of the paramagnetic moments. After a few minor temperature cycles, the sample is in a two‐phase state in which the XMCD and X‐ray linear dichroism spectra hardly depend on the temperature, and the specific electrical resistance is intermediate, showing only a weak sign of the metal–insulator transition.

Highlights

The paramagnetic metal–insulator transition in (V1–xCrx)2O3 is generally considered as the prototypical example of a Mott transition, where electronic Coulomb interactions localize the electrons in the vanadium 3d shell
We show that after a few temperature cycles the sample is in a paramagnetic metallic (PM)–PI twophase state in which the relative X-ray magnetic circular dichroism (XMCD) amplitude, the electrical resistance, and the relative XLD amplitude hardly depend on the sample temperature
XMCD spectra in the PM–PI twophase region have to be taken at these elevated temperatures where the aligned paramagnetic moments are reduced by about two orders of magnitude compared with low temperatures of a few Kelvin as described by the Brillouin function (Figure 2)

Summary

Introduction

The paramagnetic metal–insulator transition in (V1–xCrx)2O3 is generally considered as the prototypical example of a Mott transition, where electronic Coulomb interactions localize the electrons in the vanadium 3d shell. The XMCD effect manifests itself in the dependence of the intensities of an X-ray absorption spectrum on the relative orientation between the magnetization of the sample and the polarization vector of the incident circularly polarized radiation It was first investigated experimentally in 1987.[20] It can be explained in an atomic model for the absorption process, in which an electron is excited from a core state to unoccupied valence states. Changes in spectral shape and intensity are discussed in terms of orbital occupation related to the phase transition by comparison with charge transfer multiplet simulations using the CTM4XAS program package.[25] Pure thermal effects, i.e., the incomplete alignment of paramagnetic moments by the external magnetic field and the thermally induced occupation of electronic states, are discussed and the influence of hTzi is estimated. We show that after a few temperature cycles the sample is in a PM–PI twophase state in which the relative XMCD amplitude, the electrical resistance, and the relative XLD amplitude hardly depend on the sample temperature

Results and Discussion

Conclusions

Experimental Section

Conflict of Interest