The magnetic properties of GdNiAl4

Abstract DC magnetisation, electrical resistivity, specific heat and 155 Gd Mossbauer spectroscopy measurements demonstrate that the Gd sub-lattice of GdNiAl 4 undergoes two magnetic transitions ( T N = 24.7 K , T N ′ = 20.8 K ) as the temperature is decreased. Given that Gd 3+ is an S-state ion, a crystal field mechanism can be ruled out as the origin of similar behaviour observed elsewhere for RNiAl 4 with R=Pr 1− x Nd x ( 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 155 Gd nucleus, it is deduced that the magnetisation is aligned with either the b - or c -crystallographic axis of the orthorhombic structure.