Magnetic hyperfine interactions in GdAl₃

Abstract

We have studied the magnetic hyperfine interactions in GdAl₃ using¹⁵⁵Gd Mössbauer spectroscopy between the temperatures of 4K and 90K. Previous studies on GdAl₃ have shown that antiferromagnetic ordering occurs at 18K, and that a fit of the susceptibility to 1/(T-θ_p) yields a θ_p value of −89K. The large ratio of θ_p to T_N is indicative of magnetic frustration between competing ferro-and antiferromagnetic interactions, which may be due to a combination of the oscillatory nature of the RKKY interaction and the geometry of the hexagonal lattice. Our studies show that the saturation magnetic hyperfine field at the Gd site is −24.0 T, with the moments lying in the basal plane. The efg at the gadolinium site is 2.55(1)×10¹⁷V cm⁻² which is considerably larger than the value predicted by a point charge calculation. This difference may indicate that there is a conduction electron contribution. A helical magnetic structure has been calculated from RKKY theory.