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

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 Gd1-xTbx(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.