Hyperfine interaction in Co2SiO4 investigated by high resolution neutron spectroscopy

We have investigated the hyperfine interaction in Co2SiO4 by inelastic neutron scattering with a high resolution back-scattering neutron spectrometer. The energy spectrum measured from a Co2SiO4 powder sample revealed inelastic peaks at E=1.387±0.006μeV at T=3.5 K on both energy gain and energy loss sides. The inelastic peaks move gradually towards lower energy with increasing temperature and finally merge with the elastic peak at the electronic magnetic ordering temperature TN≈50K. The inelastic peaks have been interpreted to be due to the transition between hyperfine-split nuclear level of the 59Co isotopes with spin I=72. The temperature dependence of the energy of the inelastic peak in Co2SiO4 showed that this energy can be considered to be the order parameter of the antiferromagnetic phase transition. The determined hyperfine splitting in Co2SiO4 deviates from the linear relationship between the ordered electronic magnetic moment and the hyperfine splitting in Co, Co–P amorphous alloys and CoO presumably due to the presence of unquenched orbital moment. These results are very similar to those of CoF2 recently reported by Chatterji and Schneider [7].