Mössbauer Studies of Spin Flop in Antiferromagnetic Hematite

Abstract

The antiferromagnetic sublattice magnetizations below the Morin transition temperature T_M≈260°K, are parallel and antiparallel to the trigonal axis of rhombohedral α‐Fe₂O₃. Experiments at 80°K, using the Mössbauer technique together with high external magnetic fields on both polycrystalline and single‐crystal samples, show that the directions of the sublattice magnetizations flop from along the trigonal axis for the applied field H₀<H_c to perpendicular to the trigonal axis for H₀>H_c; H_c is found to be 67.5±3 kOe. In the polycrystalline sample this behavior is exhibited through the occurrence of a maximum in the width of the outer lines of the Mössbauer spectrum plotted as a function of H₀. In the single crystal, which is oriented so that the gamma rays propagate along the [111] direction, the magnetic transition is clearly observed as a sudden qualitative as well as quantitative change in the appearance of the Mössbauer hyperfine spectrum; below the critical field the Δm=0 lines are the strongest components of the six‐line spectrum.