DATASET for 'Large sub-Kelvin Magnetocaloric Effect and Phase Behavior of Gadolinium Nitrate Hexahydrate'

We report a comprehensive magnetothermal study of the classical gadolinium salt [Gd(NO3)3]·6H2O at temperatures approaching absolute zero. Despite its long-standing availability as a commercial compound, its magnetocaloric properties have remained unexplored. Using electron paramagnetic resonance, magnetic susceptibility, heat capacity, and direct measurements of the magnetocaloric effect, we reveal that weak dipolar interactions combined with axial crystal-field anisotropy drive antiferromagnetic ordering at T_N = 0.21 K. Remarkably, [Gd(NO3)3]·6H2O exhibits an isothermal magnetic entropy change of -\Delta S_m = 26.1 J / K kg at T = 0.6 K for a modest field variation of Delta-B = 1 T, and an adiabatic temperature change of Delta-T_ad = 5.0 K at T = 1.6 K for the same Delta-B, outperforming many state-of-the-art Gd-based refrigerants. These results provide a reference for understanding magnetocaloric behavior in hydrated salts and highlight the interplay between dipolar coupling and crystal-field anisotropy.