Magnetic properties of RCoO3 cobaltites (R = La, Pr, Nd, Sm, Eu). Effects of hydrostatic and chemical pressure

Abstract We have investigated the temperature dependence of the magnetic susceptibility χ ( T ) of rare-earth cobaltites RCoO 3 (R = La, Pr, Nd, Sm, Eu) in the temperature range 4.2–300 K and also the influence of hydrostatic pressure up to 2 kbar on their susceptibility at fixed temperatures T  = 78 and 300 K. The specific dependence χ ( T ) observed in LaCoO 3 and the anomalously large pressure effect (dln χ /d P ∼−100 Mbar − 1 for T  = 78 K) are analyzed in the framework of a two-level model with energy levels difference Δ. The ground state of the system is assumed to be nonmagnetic with the zero spin of Co 3+ ions, and magnetism at a finite temperature is determined by the excited magnetic spin state. The results of the analysis, supplemented by theoretical calculations of the electronic structure of LaCoO 3 , indicate a significant increase in Δ with a decrease in the unit cell volume under the hydrostatic pressure. In the series of RCoO 3 (R = Pr, Nd, Sm, Eu) compounds, the volume of crystal cell decreases monotonically due to a decrease in the radius of R 3 + ions. This leads to an increase in the relative energy Δ of the excited state (the chemical pressure effect), which manifests itself in a decrease in the contribution of cobalt ions to the magnetic susceptibility at a fixed temperature, and also in a decrease in the hydrostatic pressure effect on the susceptibility of RCoO 3 compounds, which we have observed at T  = 300 K.