Giant isotope effect on the itinerant-electron metamagnetism in YFe2(HyD1-y)4.2

The YFe₂(H_yD_1-y)_4.2 compounds (y=0,0.64,1) crystallize in the same monoclinic structure with a linear increase of the cell volume reaching 0.80% between the hydride and the deuteride. These compounds undergo a first-order magnetovolumic transition from a ferromagnetic to an antiferromagnetic structure, which is related to an itinerant electron metamagnetism (IEM) transition of one of the Fe sites that is surrounded by about 5 (H, D) atoms. A large H/D isotope effect is observed on the magnetic properties: the hydride presents a larger spontaneous magnetization and a 50% higher transition temperature T_M0 than the deuteride. This large isotope effect is attributed to the large cell volume difference between the hydride and the deuteride, which plays a dominant role due to the strong interplay between magnetic and elastic energy in IEM compounds.