Effect of pressure on the magnetic phase transition in cupric oxide

The thermal expansion has been measured on the single crystalline CuO under pressure up to 1.3 GPa. Two anomalies in the temperature dependence of thermal expansion were observed at antiferromagnetic transition temperatures, T-N1=230 K and T-N2=212 K, at ambient pressure, suggesting a strong magnetoelastic coupling in CuO. T-N2 is found to decrease with increasing pressure at a rate of dT(N2)/dP similar to-2.9 K/GPa. Detailed comparison was made with a previous study on the rapid suppression of the antiferromagnetic coupling in Cu1-xLixO. The Seebeck coefficient has been measured on Cu1-xLixO as a function of temperature. The results indicate that hole hopping is remarkably enhanced by substituting Cu with Li. The present study suggests that the suppression of the magnetic coupling both in the CuO under pressure and in Cu1-xLixO is mainly due to the enhancement of hole hopping.