MAGNETOCALORIC EFFECT IN DYSPROSIUM

The magnetocaloric effect in polycrystalline Dy was measured between 84 and 280 K in measuring fields from 1 to 7 T. These adiabatic temperature changes reflect structural changes in Dy with applied field and temperature, and include the first magnetocaloric data for a helical antiferromagnet. These measurements were made to evaluate Dy as working material in magnetic refrigeration applications. Above TN (179 K) a field increase always causes heating; below TN fields less than about 2 T cause cooling for some values of initial temperature. The largest temperature increase with a 7 T field occurs at the Neel point (-T=11.5 K), and at fields below 2 T near the Curie point (-T=2 K at 100 K). For refrigeration purposes, the optimal working region for a Dy cooling element is field dependent. This Dy data suggests that, because of complex magnetic structure changes, antiferromagnetic rare earths may be useful for refrigeration over a broad temperature range near TN at very high fields, and may be preferable to ferromagnetic materials over certain restricted temperature regions above the Curie point in low fields produced by permanent magnets (?1 T).