Rotating magnetocaloric effect in highly anisotropic TbIII and DyIII single molecular magnets

Abstract

The magnetocaloric effect (MCE) was investigated in highly anisotropic single crystals of two single molecule magnets (SMMs): [LnIII(ZnIIL)2]CF3SO3, where Ln = Tb, Dy and L = tripodal hexadentate Schiff base ligand. The structure of these paramagnetic compounds consists of identically oriented linear trinuclear clusters in a trigonal system with an easy direction c∥Zn–Ln–Zn array and a hard plane ab⊥Zn–Ln–Zn array. The magnitude of MCE measured for c∥H was significantly greater than MCE for ab∥H at a wide temperature range regardless of the studied SMM. Therefore, the rotating magnetocaloric effect (RMCE) was evaluated. The maxima of the magnetic entropy change for RMCE were obtained at 2.0 K and moderate fields: 3.9 J K−1 kg−1 at µ0H = 1.3 T for Ln = Tb and 3.3 J K−1 kg−1 at µ0H = 1.1 T for Ln = Dy. The relative efficiency of RMCE compared to the MCE measured in c∥H was as high as 99% at low magnetic fields.

Dy(OH)3: a paramagnetic magnetocaloric material for hydrogen liquefaction

“…Correlations between magnetic entropy changes, sample alignment and applied magnetic field directions have previously been reported in materials with strong magnetic anisotropy. 56–58 Regardless of the field change applied −Δ S m decreases rapidly below 3.5 K, as would be anticipated since the emergence of long range ferromagnetic order will greatly decrease the entropy change under applied fields.…”