Effects of temperature and pressure on the spin state of cobalt ions in La1–xPrxCoO3 compounds
A.S. Panfilov, A.A. Lyogenkaya, G.E. Grechnev, V.A. Pashchenko, L.O.
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Nauky Ave., Kharkiv 61103, Ukraine
Vasylechko, V.M. Hreb
Lviv Polytechnic National University, 12 S. Bandera Str., Lviv 79013, Ukraine
Department of Materials and Ceramic Engineering, CICECO-Aveiro Institute of Materials University of Aveiro, 3810-193 Aveiro, Portugal
Received October 29, 2019, published online April 24, 2020
For perovskite type compounds La1–xPrxCoO3 (x = 0, 0,1, 0,2, and 0,3), we have studied the crystal structure and temperature dependence of magnetic susceptibility, χ(T), in the temperature range of 5–400 K, as well as the effect of hydrostatic pressure on χ at fixed temperatures T = 78, 150 and 300 K. The obtained experimental data were analyzed in the framework of a two-level model with an energy gap Δ between the ground and excited states of the system, which correspond to S = 0 and S = 1 spin values of Co3+ ions. In this model, the magnetism of Co3+ ions, which, in particular, determines the features of the χ(T) dependence, is originated from the temperature-induced change in population of the excited state. The observed anomalously large magnitude of the pressure effect is due to the strong dependence of the excited state energy Δ on the lattice volume changes under the influence of both hydrostatic pressure and chemical contraction upon substitution of La for Pr having smaller ion size. The supplemented theoretical calculations of the electronic structure for the boundary compounds LaCoO3 and PrCoO3 confirm a significant increase in Δ with a decrease in the lattice volume, giving also evidence in favour of scenario of the spin crossover between low and intermediate spin states of the cobalt ions.
Key words: RCoO3 compounds, spin crossover, magnetic measurements, high-pressure effects, electronic structure calculations.