Tuning Magnetic and Structural Transitions through Valence Electron Concentration in the Giant Magnetocaloric Gd5–x Eu x Ge4 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 Gd5–x Eu x Ge4 system. Gd4.75Eu0.25Ge4 and Gd4.50Eu0.50Ge4 undergo temperature-induced magnetostructural transformations accompanied by giant magnetocaloric effects.