Adiabatic Demagnetization with Yttrium-Rare Earth Alloys

Alloys of yttrium with 0.3 and 1.0 atomic percent gadolinium, 1.0 at.% dysprosium, and 0.6 and 1.0 at.% holmium have been investigated to determine their usefulness as the working substance for adiabatic demagnetization. In addition, single crystals of 0.6 and 1.0 at.% holmium-yttrium alloys were studied. Those alloys which exhibited paramagnetic susceptibility behavior in the temperature range 1.2-4.2°K were demagnetized adiabatically from about 11 koe and 1.25°K. The lowest temperature attained was 0.76°K for the single crystal of 1.0 at.% holmium with the magnetic field parallel to the $a$ axis of the hexagonal crystal. Magnetization measurements obtained for the single crystals in the temperature range 1.2-4.2°K indicated strong anisotropy with the $a$ axis as the easy axis of magnetization. Hysteresis was observed in the magnetization of the 1.0 at.% holmium single crystal with the $a$ axis parallel to the field. Entropy removal during magnetization was calculated from the magnetization data for the single crystals and found to be only about 15% of that expected if the alloy behaved like an ideal paramagnetic substance.