PRESSURE AND TEMPERATURE ELECTRON-PARAMAGNETIC-RESONANCE STUDIES OF CS2NALACL6-GD3(+) CRYSTAL

The effect of temperature and hydrostatic pressure on the spin-Hamilto nian parameter b(4)(0) for Gd3+ in elpasolite Cs2NaLaCl6 is studied up to a pressure of 700 MPa over the temperature range 180-360 K. It is found that 56% of the temperature change in b(4)(0)(T) is caused by th e spin-phonon interaction, and the remaining 44% is related to the the rmal expansion of the crystal. The temperature at which the phase tran sition from the cubic to the tetragonal phase occurs (T-c = 207 K) is a linear function of pressure, with the pressure coefficient dT(c)/dp = 53 +/- 0.6 K GPa(-1). The dependence of T-c on the lattice constant and hydrostatic pressure is interpreted within the rigid-sphere model. No precursive behaviour above T-c is observed.