Searching beyond Gd for magnetocaloric frameworks: magnetic properties and interactions of the Ln(HCO2)3 series

Abstract

This study probes the magnetic properties and interactions of the Ln(HCO₂)₃ (Ln = Tb³⁺–Er³⁺) frameworks. We show that the magnetocaloric effect of Tb(HCO₂)₃ is significantly higher above 4 K in moderate magnetic fields compared to the promising Gd(HCO₂)₃. While the peak performance of Tb(HCO₂)₃ is lower than Gd(HCO₂)₃, we also find that the Gd-rich members of the solid solution Gd_1−xTb_x(HCO₂)₃ blend the advantages of both end-members. Using neutron diffraction experiments, Tb(HCO₂)₃ is found to be antiferromagnetic below 1.7 K with ferromagnetic face-sharing chains and antiferromagnetic coupling between them. Analysis of magnetic diffuse scattering of the paramagnetic phase indicates that ferromagnetic coupling is retained, and it is likely that this plays a role in improving its magnetocaloric performance in low fields.