A STUDY OF MAGNETOELECTRIC DOMAIN FORMATION IN CR2O3

The newly developed technique of zero-held neutron polarimetry has bee n used to determine the imbalance in the population of 180 degrees dom ains in antiferromagnetic Cr2O3 produced by cooling through the Neel t emperature under different conditions. The method allows the absolute spin configuration of the preferred domain to be determined. In the st ructure of Cr2O3 the Cr3+ ions distributed along the trigonal axes in pairs across the centres of symmetry; in the antiferromagnetic phase t heir moments are aligned parallel and antiparallel to this axis. it is found that although a magnetic field applied parallel to this axis du ring cooling is able to change the domain populations, these changes a re neither reversible nor completely predictable. On the other hand, c ooling with combined electric and magnetic fields along the trigonal a xis leads to much more consistent results, and virtually single-domain crystals of either type can be obtained. The type of domain produced depends on whether the electric and magnetic fields are parallel or an tiparallel. When the sample is cooled in parallel fields, the domain p roduced is that in which the magnetic moments on the Cr3+ ions of each closely spaced pair point towards one another. The different atomic p erturbations which lead to a magnetoelectric effect are discussed and it is shown that the g-factor process can give the observed magnetoele ctric annealing effect.