Local electronic structure of the Co2+ ions in the disordered perovskite phase of Ba3CoNb2O9: a temperature-dependent X-ray absorption and magnetic circular dichroism study

Abstract

We performed temperature-dependent X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) measurements on the disordered phase of Ba${}_3$CoNb${}_2$O${}_9$ to determine the local electronic structure of the Co${}^{2+}$ ions. We employed the line-fitting inverse partial fluorescence yield (iPFY) method to obtain reliable spectra from this insulating material. From the comparison between the experimental spectra and full multiplet cluster calculations we were able to constrain the local crystal-field environment and assess the spin-orbit-entangled nature of the Co${}^{2+}$ ground state. In this chemically disordered system, the Co${}^{2+}$ ions retain on average an effectively cubic crystal-field environment that supports a $J_{\mathrm{eff}}=1/2$ ground state. These results further establish that Ba${}_3$CoNb${}_2$O${}_9$ is a promising platform for investigating the effect of disorder on $J_{\mathrm{eff}}=1/2$ magnetism.