Enhancing Magnetic Functionality with Scandium: Breaking Stereotypes in the Design of Rare Earth Materials

Replacement of strongly magnetic gadolinium with weakly magnetic scandium unexpectedly enhances ferromagnetic interactions in (Gd_1–xSc_x)₅Ge₄. Based upon this counterintuitive experimental finding we demonstrate the unique role 3d¹ electrons of scandium atoms play in mediating magnetic interactions between the gadolinium atoms from the neighboring layers in the Sm₅Ge₄-type crystal lattice. Scandium substitutions at and below 20% rapidly increase the Curie temperature, T_C, of the Gd₅Ge₄ parent, eliminate both the kinetic arrest and hysteresis, and drastically improve reversibility of the first-order magnetostructural transformation at T_C. In agreement with first-principles predictions, higher than 20% Sc leads to the formation of a closely related Pu₅Rh₄-type structure where the first-order magnetostructural transformation is replaced by a conventional second-order ferromagnetic ordering that remains accompanied by a continuous rearrangement of the crystal lattice. Comparison of two materials with similar structures and compositions shows that significantly stronger magnetocaloric effect occurs in the first-order material, which also shows very small hysteresis. Furthermore, we demonstrate that a behavior of a specific interatomic distance can predict anomalous physical properties in a series of alloys where compositional dependence of lattice parameters suggests a rather trivial solid solubility and uninteresting magnetism.