The magnetic properties of GdNiAl4

DC magnetisation, electrical resistivity, specific heat and 155Gd Mössbauer spectroscopy measurements demonstrate that the Gd sub-lattice of GdNiAl4 undergoes two magnetic transitions (TN=24.7K, TN′=20.8K) as the temperature is decreased. Given that Gd3+ is an S-state ion, a crystal field mechanism can be ruled out as the origin of similar behaviour observed elsewhere for RNiAl4 with R=Pr1−xNdx (0⩽x⩽0.7) and Tb. Based on a comparison of point charge model calculations of the electric field gradient tensor with those measured at the 155Gd nucleus, it is deduced that the magnetisation is aligned with either the b- or c-crystallographic axis of the orthorhombic structure.