Experimental Study of Magnetocaloric Effect in Tetraaquabis(Hydrogen Maleato)Nickel(II), [Ni(C4H3O4)2(H2O)4]—A Potential Realization of a Spin-1 Spatially Anisotropic Square Lattice with Ferromagnetic Interactions

An experimental study of the magnetocaloric effect in tetraaquabis(hydrogen maleato)nickel(II), [Ni(C4H3O4)2(H2O)4] powder sample is presented. The properties studied were investigated using specific heat and magnetization measurements magnetic fields up to 9 T temperature range from 0.4 50 K. A large conventional was found at a about 3.5 K, where ??SM = 8.5 Jkg?1K?1 11.2 for field 5 7 T, respectively. Assuming substantial role crystal field, dependence zero compared with an S 1 model single-ion anisotropy parameters D E (axial rhombic). best agreement D/kB ?7.82 K E/kB ?2.15 On other hand, shows higher values theoretical prediction mentioned model, indicating presence additional factors system, such as exchange interaction between ions. first pathway can be realized through maleic rings nearest Ni(II) second water molecules approximately along crystallographic axis. Broken-symmetry DFT calculations performed computational package ORCA provided ferromagnetic interactions, J1/kB 1.50 J2/kB 1.44 (using B3LYP functional). correlations system may explain enhanced anisotropic spin-1 paramagnet.