ANTIFERROMAGNETISM OF GAMMA FEOOH - A MOSSBAUER EFFECT STUDY

Measurements of the Mössbauer spectra of γ FeOOH show that it is an antiferromagnet with a Néel temperature of 73°K. The hyperfine field at the 57Fe nuclei is 460±5 kG. By applying an external magnetic field to a single crystal the Fe3+ magnetic moments are shown to be collinear in the antiferromagnetic state, with the alignment along the c axis. From measurements in the paramagnetic state using polarized γ radiation the electric field gradient is shown to be negative in sign, and its major axis lies in the ac plane making an angle of about 55°with the c axis.