Antiferromagnet-ferromagnet transitions in Ge-rich Gd-5(SixGe(4-x)) alloys induced by composition, magnetic field, and temperature

Temperature and magnetic-field dependences of zero-field-cooled (ZFC) Ge-rich Gd-5(SixGe4-x) alloys with a distinctly layered crystal structure have been studied. At 4.2 K, alloys with x < 0.1 show an antiferromagnetic state, which can be irreversibly transformed to a ferromagnetic state by a magnetic field. In contrast, ZFC alloys with x >= 0.1 already have a ferromagnetic state. All alloys being in ferromagnetic state then exhibit a temperature-induced first-order ferromagnet -> antiferromagnet transition at T-tr. ZFC Gd-5(SixGe4-x) alloys with either antiferromagnetic or ferromagnetic initial state at 4.2 K also exhibit a second-order reversible antiferromagnet <> paramagnet transition at the Neel temperature T-N approximate to 128 K. Magnetic phase transition induced by a magnetic field at T-tr is determined by the exchange interactions between Gd magnetic moments located in the nearest slabs rather than those located in the same slab and can be described by Landau model of antiferromagnets. Similar magnetic correlations between Gd magnetic moments in the Ge-rich Gd-5(SixGe4-x) alloys can be induced either by the internal (composition) or by the external (magnetic field, temperature, and hydrostatic pressure) effects. It is likely that dipole-dipole interactions between magnetically ordered nearest slabs contribute to magnetic phase transitions.