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.