ESR measurements of GdBi

Electron spin resonance (ESR) measurements on a single crystal of GdBi have been performed using a vector network analyzer (VNA) in the frequency range between 57 and 107 GHz, in the temperature range from 50 to 1.7 K and in magnetic fields up to 14 T using a superconducting magnet to obtain the microscopic information about the basic magnetic properties. Above 15 K, the observed absorption corresponds to g=2.0 of Gd3+. However, the resonance field shifts to lower field with decreasing temperature from 4.2 K, which cannot be explained by 'usual' antiferromagnetic resonance (AFMR) modes but suggests that the hyperfine field due to the Bi nuclear moments affects the AFMR of GdBi. The estimated values of the anisotropy field and the hyperfine anisotropy field are Ba=5.6x10-4 T and Bn=7.9x10-3 T, respectively, at 4.2 K