MAGNETIC PHASES AND MAGNETOELASTIC PHENOMENA IN UNIGA UNDER PRESSURE

UNiGa exhibits several antiferromagnetic (AF) phases below T-N=39 K. T he related magnetic phase transitions cause pronounced thermoexpansion anomalies of opposite sign for the c- and a-axes, respectively, leavi ng volume effects nearly negligible. Magnetic fields applied along the c-axis induce transitions from the AF phases to an uncompensated AF a nd/or to a ferromagnetic (F) phase accompanied by magnetostriction eff ects. Our results on pressure influence on the thermoexpansion and mag netostriction anomalies allow us to propose a tentative p-T magnetic p hase diagram. A new AF phase induced by pressures above 1.8 GPa has be en found. Neutron-diffraction studies under hydrostatic pressure up to 0.9 GPa and in magnetic fields up to 2 T confirmed that the critical temperatures and the critical fields of transitions of UNiGa are stron gly pressure dependent (some phases are even suppressed) although rele vant magnetic structures themselves remain essentially unchanged. (C) 1998 Elsevier Science S.A.