Coexistence of short-range ferromagnetic and antiferromagnetic correlations in Ge-rich Gd₅(Si_xGe_1−x)₄ alloys

Isothermal magnetization curves up to 23 T were measured in Gd-5(SixGe1-x)(4)alloys for x <= 0.1. We show that a field-induced transition occurs from the antiferromagnetic (AFM) phase to a state in which competing short-range AFM and ferromagnetic (FM) correlations are present. This is based on the abrupt change in the slope of the high-temperature magnetization isotherms at high fields (similar to 14-15 T). Results suggest that the transition is due to the breaking of the long-range AFM ordering by the magnetic field. This induces short-range FM correlations favouring the formation of coexisting FM and AFM clusters. A further increase of the magnetic field leads to the percolation of the former, giving rise to long-range FM order.