Tuning Magnetic and Structural Transitions through Valence Electron Concentration in the Giant Magnetocaloric Gd_5–xEu_xGe₄ Phases

Valence electron concentration is a viable chemical tool to control the crystal structure and magnetism of Gd₅Ge₄. A decrease in the valence electron concentration achieved through the substitution of Eu²⁺ for Gd³⁺ leads to the formation of the interslab Ge–Ge dimers, phase transitions to the Gd₅Si₂Ge₂- and Gd₅Si₄-type structures, and a ferromagnetic ordering in the Gd_5–xEu_xGe₄ system. Gd_4.75Eu_0.25Ge₄ and Gd_4.50Eu_0.50Ge₄ undergo temperature-induced magnetostructural transformations accompanied by giant magnetocaloric effects.