Optimization of the Magnetocaloric Effect in Low Applied Magnetic Fields in LnOHCO 3 Frameworks

This study probes the structure and magnetocaloric effect of the LnOHCO 3 (Ln = Gd 3+, Tb 3+, Dy 3+, Ho 3+, and Er 3+ ) frameworks. The combination of single crystal X-ray and neutron powder diffraction indicates that these materials solely adopt the P 2 1 2 1 2 1 structure under these synthetic conditions and magnetic susceptibility measurements indicate they remain paramagnetic down to 2 K. We show that the magnetocaloric effects of TbOHCO 3 and DyOHCO 3 have peak entropy changes of 30.99 and 33.34 J kg –1 K –1 for a 2–0 T field change, respectively, which are higher than that of the promising GdOHCO 3 framework above 4 K in moderate magnetic fields. The magnetic entropy changes of TbOHCO 3 and DyOHCO 3 above 4 K for smaller than 2 T field changes also exceed those of Gd 3 Ga 5 O 12 and Dy 3 Ga 5 O 12, 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.