Pressure effect on magnetic susceptibility of LaCoO${}_3$

The effect of pressure on magnetic properties of LaCoO${}_3$ is studied experimentally and theoretically. The pressure dependence of magnetic susceptibility $\chi$ of LaCoO${}_3$ is obtained by precise measurements of $\chi$ as a function of the hydrostatic pressure $P$ up to 2 kbar in the temperature range from 78 K to 300 K. A pronounced magnitude of the pressure effect is found to be negative in sign and strongly temperature dependent. The obtained experimental data are analysed by using a two-level model and DFT+U calculations of the electronic structure of LaCoO${}_3$. In particular, the fixed spin moment method was employed to obtain a volume dependence of the total energy difference $\mathrm{\Delta }$ between the low spin and the intermediate spin states of LaCoO${}_3$. Analysis of the obtained experimental $\chi (P)$ dependence within the two-level model, as well as our DFT+U calculations, have revealed the anomalous large decrease in the energy difference $\mathrm{\Delta }$ with increasing of the unit cell volume. This effect, taking into account a thermal expansion, can be responsible for the temperatures dependence of $\mathrm{\Delta }$, predicting its vanishing near room temperature.