Large magnetic anisotropy and a rotating cryomagnetocaloric effect in single-crystalline paramagnetic lanthanide calcium oxyborates LnCa4O(BO3)3 with Ln = Pr, Nd, Gd, Er, and Tm

Abstract

Lanthanide calcium oxyborate LnCa₄O(BO₃)₃ compounds form a family of multifunctional materials with promising nonlinear and linear optical properties and piezoelectric properties because of their polar crystal structure. In the present work, we report their anisotropic magnetic properties through the study of single-crystalline lanthanide calcium oxyborate LnCa₄O(BO₃)₃ samples with Ln = Pr, Nd, Gd, Er and Tm. A strong magnetic anisotropy was observed, mostly originating from the strong single-ion anisotropy and varies significantly from one magnetic Ln³⁺ ion to another. This causes a large rotating magnetocaloric effect (RMCE) in the helium liquid temperature range for the Nd, Er and Tm compounds. For the Nd and Er compound, the RMCE is larger than the polycrystalline MCE up to the largest investigated magnetic field, 7 T, whereas the RMCE is larger than the polycrystalline value below 4 T for the Tm and Er compounds. The RMCE of the Er compound also exceeds any polycrystalline MCE in this compound family below 3 T. This shows the exceptional potential of Er-based LnCOB for RMCE applications in the liquid He temperature range.