Rotating Magnetocaloric Effect in an Anisotropic Molecular Dimer

In contrast to the mainstream research on molecular refrigerants that seeks magnetically isotropic molecules, we show that the magnetic anisotropy of dysprosium acetate tetrahydrate, [{Dy(OAc)(3)(H2O)(2)}(2)]4H(2)O (1), can be efficiently used for cooling below liquid-helium temperature. This is attained by rotating aligned single-crystal samples in a constant applied magnetic field. The envisioned advantages are fast cooling cycles and potentially compact refrigerators.