The three‐dimensional metal–organic framework Gd(HCOO)₃ is characterized by a relatively compact crystal lattice of weakly interacting Gd³⁺ spin centers interconnected via lightweight formate ligands, overall providing a remarkably large magnetic:non‐magnetic elemental weight ratio. The resulting magnetocaloric effect per unit volume is decidedly superior in Gd(HCOO)₃ than in the best known magnetic refrigerant materials for liquid‐helium temperatures and low‐moderate applied fields.

The magnetic ordering structure of ${\mathrm{GdPO}}_4$ is determined at $T=60$ mK by the diffraction of hot neutrons with wavelength $\lambda =0.4696$ Å. It corresponds to a noncollinear antiferromagnetic arrangement of the Gd moments with propagation vector $\mathbf{k}=(1/2,0,1/2)$. This arrangement is found to minimize the dipole-dipole interaction and the crystal-field anisotropy energy, the magnetic superexchange being much smaller. The intensity of the magnetic reflections decreases with increasing temperature and vanishes at $T\approx 0.8$ K, in agreement with the magnetic ordering temperature $T_N=0.77$ K, as reported in previous works based on heat capacity and magnetic susceptibility measurements. The magnetocaloric parameters have been determined from heat capacity data at constant applied fields up to 7 T, as well as from isothermal magnetization data. The magnetocaloric effect, for a field change $\Delta B=0-7\mathrm{T}$, reaches $-\Delta S_T=375.8\mathrm{mJ}/{\mathrm{cm}}^3{\mathrm{K}}^{-1}$ at $T=2.1$ K, largely exceeding the maximum values reported to date for Gd-based magnetic refrigerants.

The magnetothermal properties of a coordination polymer and a metal–organic framework (MOF) based on Gd³⁺ ions are reported. An equally large cryogenic magnetocaloric effect (MCE) is found, irrespective of the dimensionality. This combined with their robustness makes them appealing for widespread magnetic refrigeration applications.

We have investigated the magnetocaloric effect in single and polycrystalline samples of quantum paraelectric $\mathrm{EuTi}{\mathrm{O}}_3$ by magnetization and heat capacity measurements. Single crystalline $\mathrm{EuTi}{\mathrm{O}}_3$ shows antiferromagnetic ordering due to $\mathrm{E}{\mathrm{u}}^{2+}$ magnetic moments below $T_{\mathrm{N}}=5.6\mathrm{K}$. This compound shows a giant magnetocaloric effect around its Néel temperature. The isothermal magnetic entropy change is $49\mathrm{J}{\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$, the adiabatic temperature change is 21 K, and the refrigeration capacity is $500\mathrm{J}{\mathrm{kg}}^{-1}$ for a field change of 7 T at $T_{\mathrm{N}}$. The single crystal and polycrystalline samples show similar values of the magnetic entropy and adiabatic temperature changes. The large magnetocaloric effect is due to suppression of the spin entropy associated with the localized $4f$ moment of $\mathrm{E}{\mathrm{u}}^{2+}$ ions. The giant magnetocaloric effect, together with negligible hysteresis, suggest that $\mathrm{EuTi}{\mathrm{O}}_3$ could be a potential material for magnetic refrigeration below 40 K.

We characterize supramolecular magnetic structures, consisting of two weakly coupled antiferromagnetic rings, by low-temperature specific heat, susceptibility, magnetization and electron paramagnetic resonance measurements. Intra- and inter-ring interactions are modeled through a microscopic spin-Hamiltonian approach that reproduces all the experimental data quantitatively and legitimates the use of an effective two-qubit picture. Spin entanglement between the rings is experimentally demonstrated through magnetic susceptibility below 50~mK and theoretically quantified by the concurrence.