Mössbauer Effect in α‐Fe 2 O 3

Experimental data are obtained for the antiferromagnetic compound α‐Fe 2 O 3 by the Mössbauer technique. α‐Fe 2 O 3 exhibits interesting properties, viz. the quantization axis of the spins of the iron ions changes direction by 90° at T t = 260 °K, and the between 260 °K and the Néel temperature of 956 °K it shows weak ferromagnetism. The changes of the internal fields at the transition temperature are studied in detail. The effective magnetic field H eff drops abruptly by 8 kOe on heating α‐Fe 2 O 3 through the transition temperature. Furthermore, the curve of H eff against T shows temperature hysteresis around T t . An explanation for the discontinuity in H eff at T t can be given on the basis of a small asymmetry of the charge distribution of the 3d‐electrons of the Fe 3+ ions; this produces a contribution on the effective magnetic field of the orbital and spin magnetic moments of these electrons which is in addition to the contact field. The temperature dependence of H eff is also determined and cannot be described in terms of a Brillouin curve for S = 5/2.