Magnetic transitions in disordered GdAl₂

The role of disorder in magnetic ordering transitions is investigated using mechanically milled GdAl ₂ . Crystalline GdAl ₂ is a ferromagnet while amorphous GdAl ₂ is a spin glass. Nanostructured GdAl ₂ shows a paramagnetic-to-ferromagnetic transition and glassy behavior, with the temperature and magnitude of each transition dependent on the degree and type of disorder. Disorder is parametrized by a Gaussian distribution of Curie temperatures T _C with mean T _C and breadth Δ T _C . A nonzero coercivity is observed at temperatures more than 20 K above the highest T _C of any known Gd-Al phase; however, the coercivity decreases with decreasing temperature over the same temperature range where the GdAl ₂ grains ferromagnetically order. Models for the anomalous coercivity behavior are proposed and evaluated for their ability to explain the origin of the low-temperature glassy magnetization peak.