PRESSURE-DEPENDENCE OF THE 100 K SPIN-STATE TRANSITION IN LACOO3

The pressure dependence of the 100 K spin-state transition in LaCoO3 i s investigated through magnetization measurement under pressures of up to 18.2 kbar. The energy gap, Delta, between the low-spin ground stat e and the excited magnetic state (intermediate spin) increases remarka bly with increasing pressure. The linear part of the pressure dependen ce of Delta, which is dominant below 5 kbar, is interpreted consistent ly by the volume expansion due to the spin-state transition under ambi ent pressure. In the higher pressure region, a quadratic pressure depe ndence is dominant, which suggests a Very steep volume dependence of t he energy of the excited magnetic state under the highly compressed co ndition.