Spin transition in LaCoO3 investigated by resonant soft X-ray emission spectroscopy

– The spin transition in LaCoO3 is investigated by temperature-dependent resonant soft X-ray emission spectroscopy near the Co 2p absorption edges. This element-specific technique is more bulk sensitive with respect to the temperature-induced spin state of the Co ions in LaCoO3 than other high-energy spectroscopic methods. The spin transition is interpreted and discussed with ab initio density-functional theory within the fixed-spin moment method, which is found to yield consistent spectral functions to the experimental data. The spectral changes for LaCoO3 as a function of temperature suggest a change in spin state as the temperature is raised from 85 to 300K, while the system remains in the same spin state as the temperature is further increased to 510K. The interest in transition metal oxides has grown significantly in several branches of solidstate physics. Recent investigations have shown that some of these systems exhibit a variety of fascinating properties, e.g., high-temperature superconductivity in the cuprates and colossal magneto-resistance in the manganates [1]. For the cobaltates, one of the most important phenomena is the temperature-induced spin transition in LaCoO3 [2–4]. This material is unique in the sense that it undergoes one or more spin state transition(s) with increasing temperature and has therefore attracted attention as a compound with peculiar magnetic properties. Although the history of the issue of the spin transition(s) in LaCoO3 is quite long, the controversy has not yet completely settled down. One reason is difficulties of precise electronic-structure measurements at high temperatures above ∼ 500K. Depending on the method used, the literature reveals several conflicting interpretations with respect to which temperature the spin state transition(s) takes place. Studies using valence band X-ray photoelectron spectroscopy (XPS) [5, 6] and X-ray absorption spectroscopy (XAS) [7] have been performed at different temperatures up to about ∼ 600K. In a quasi-ionic picture, the ground state of LaCoO3 at 4.2K has Co ions in the 3d configuration which form a singlet S = 0, t2g low-spin (LS) state. The changes in the spectra have been interpreted to be due to thermal population into a S = 2, t2ge 2 g high-spin (HS) state from the LS state [5, 7, 8]. However, both XPS and