Mössbauer Effect in α‐Fe2O3

Experimental data are obtained for the antiferromagnetic compound α‐Fe2O3 by the Mössbauer technique. α‐Fe2O3 exhibits interesting properties, viz. the quantization axis of the spins of the iron ions changes direction by 90° at Tt = 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 Heff drops abruptly by 8 kOe on heating α‐Fe2O3 through the transition temperature. Furthermore, the curve of Heff against T shows temperature hysteresis around Tt. An explanation for the discontinuity in Heff at Tt can be given on the basis of a small asymmetry of the charge distribution of the 3d‐electrons of the Fe3+ 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 Heff is also determined and cannot be described in terms of a Brillouin curve for S = 5/2.