Influence of Hydrostatic Pressure on Magnetic Transitions in Terbium and Dysprosium

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Abstract
The effect of hydrostatic pressure on the magnetic transitions in terbium and dysprosium has been investigated. The transformer method is used, in which the toroidal core of the miniature transformer is the rare-earth metal itself. Results are obtained as curves of secondary voltage versus temperature. A cusp in the secondary voltage indicates the occurrence of a Néel temperature, at which a transformation takes place from a paramagnetic to an antiferromagnetic state, while a sharp rise in the secondary voltage indicates the passage through a Curie temperature, where a transformation from an antiferromagnetic to a ferromagnetic state occurs. The pressures, up to 25 kbar, are obtained by the piston-cylinder technique, using silver chloride as the pressure-transmitting medium. The temperature range is from 40°K to room temperature. This has been achieved with the use of a new 4-wall cryogenic Dewar and liquid helium as coolant. The pressure co-efficient of the transition temperature of terbium is found to be -1.0°K/kbar. Under pressure, the atmospheric Néel temperature either disappears or, because of the narrowness of the antiferromagnetic region, is difficult to separate from the Curie temperature. The pressure coefficient of the Néel temperature for dysprosium is -0.4°K/kbar. In the range of from zero to about 7 kbar, the Curie temperature appears to increase with increasing pressure; beyond 7 kbar, the Curie temperature appears to decrease with increasing pressure. In the low-pressure range, the pressure coefficient of the Curie temperature appears to be positive, and in the high-pressure range it is -0.8°K/kbar. The above results involving measurements on dysprosium must be taken as tentative. The shape of the secondary-voltage-versus-temperature curves is such that one cannot assign the coefficients in an unambiguous manner.