A Mössbauer Study of the Internal Field at Fe57 in α-Fe2O3

Mössbauer absorption by Fe 57 in α-Fe 2 O 3 has been measured as a function of temperature from 100°K to 1050°K. In the hyperfine spectra, a steep change of the energy shift ε due to quadrupole interaction was found at about 260°K. The ratio of ε at 100°K to that at 300°K is -2.0±0.4. This value corresponds to the ratio of (3cos 2 θ-1) below and above the transition temperature, if we assume that the direction of the principal axis of the electric field gradient at the iron nucleus is parallel to the c axis. A careful observation of the shape of the absorption line near the transition temperature showed that each line consisted of doublet respectively. This fact reveals that the transition temperature of α-Fe 2 O 3 used in the present experiment varies locally from 220°K to 270°K. The value of e 2 q Q obtained at about 260°K is (+0.084±0.008) cm/sec=(+9.7±0.9) Mc/sec. Although there were fairly large errors in the obtained values of e 2 q Q , thefild gradient seemed to increase slowly with temperature from 100°K to 700°K. Theabrupt increse of the field gradient was found near the Néel temperature. The observed temperature dependence of the internal magnetic field was fairly consistent with the molecular field theory for S =5/2.