Effect of Gd polarization on the large magnetocaloric effect of GdCrO4 in a broad temperature range.

The ferromagnetic zircon-type phase of GdCrO4 presents high values for the magnetocaloric (MC) parameters. This compound has large isothermal entropy changes Delta S-T under the magnetic field action in a wide temperature range, from 5 to 35 K, reaching a maximum vertical bar Delta S-T vertical bar = 29.0 +/- 0.1 J/kgK at 22 K, for a field increment Delta B = 9 T. It orders ferromagnetically at T-C = 21.3 K via the Cr-Cr exchange interaction and shows a second transition at 4.8 K due to the ordering of the Gd sublattice. The large MC effect is enhanced by the polarization of the Gd3+ ions by the Cr5+ ones via a weaker Gd-Cr interaction. This effect is an interesting feature to be considered in the search for new compounds with a high MC effect in the range of liquid hydrogen or natural gas, regarding the liquefaction of gases by magnetization-demagnetization cycles. This paper contains experimental measurements of magnetization, heat capacity, and direct determinations of the MC effect. The magnetic contribution to the heat capacity C-m has been obtained after subtracting the lattice component. Approximate values for the exchange constants J(1) (Cr-Cr) and J(3) (Gd-Cr) have been deduced from C-m.