Uniaxial pressure effect on the magnetic phase diagram and Fermi-surface properties of CeB₆

The magnetic phase diagram and the de Haas-van Alphen (dHvA) effect of CeB₆ have been studied under uniaxial pressures and magnetic fields applied parallel to [001]. Two phases IIA and IIB in the antiferroquadrupolar (AFQ) state and three phases III″, III and III′ in the antiferromagnetic (AFM) state are found. With application of a small uniaxial pressure, the low-field phases IIA and III″ change drastically and are likely to disappear. On the other hand, the AFQ transition temperature for the high-field phase IIB does not change within experimental error. The AFM transition temperature for phase III, the transition field between phases III and III″, III″ and paramagnetic phases all increase with uniaxial pressure. The dHvA frequency increases with uniaxial pressure, whereas it is expected to decrease from the area change of the reciprocal space. The effective mass increases rapidly with uniaxial pressure at low pressures and then does not change appreciably at high pressures. The present observations of the uniaxial pressure effects are qualitatively different from those of hydrostatic pressure effects. By comparing the hydrostatic and uniaxial pressure effects, we argue that the compressions along the [001] direction and in the (001) plane give very different effects, reflecting the quadrupolar order.