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.