Optimisation of the Magnetocaloric Effect in Low Applied Magnetic Fields in LnOHCO3 Frameworks

This study probes the structure and magnetocaloric effect of the LnOHCO3 (Ln = Gd3+, Tb3+, Dy3+, Ho3+ and Er3+) frameworks. A combination of single crystal X-ray and neutron powder diffraction indicate that these materials solely adopt the P212121 structure under these synthetic conditions and magnetic susceptibility measurements indicate they remain paramagnetic down to 2 K. We show that the magnetocaloric effect of TbOHCO3 and DyOHCO3 have a peak entropy change of 30.99 and 33.34 J Kg-1 K-1 for a 2-0 T field change respectively, which is higher than than the promising GdOHCO3 framework above 4 K in moderate magnetic fields. The magnetic entropy change of TbOHCO3 and DyOHCO3 above 4 K for sub-2T field changes also exceeds that of Gd3Ga5O12 and Dy3Ga5O12, making them suitable magnetic cooling materials for use at liquid helium temperatures using the low applied magnetic fields accessible using permanent magnets, advantageous for efficient practical cooling devices.