Magnetoelectric Effect in Magnetic Materials
K. Siratori, K. Kohn, E. Kita
1992
Acta Physica Polonica. A
Magnetoelectric effect in magnetic insulators is reviewed. Alter an intuitive explanation of the effect in antiferromagnetic Cr 2 O3, the following topics are discussed on the experiments. Measurement and controlling of antiferromagnetic domains as well as antiferromagnetic domain wall motion. Expansion of the free energy of crystals in terms of magnetic and electric fields and polarizations. Information on the magnetic symmetry of crystals. Investigation of mechanisms of magnetoelectric
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... Excited states and optical observation. PACS numbers: 75.80.+q (431) Μagnetoelectric Effect in Magnetic Materials 433 An intuitive consideration A case study of Cr2O3 Let us start from Cr2 O3, the starting material of the investigation. Figure 1 shows the corundum structure of this crystal. The point symmetry is rhombohedral Ric, with a unit cell containing four crystallographically equivalent cations, octahedrally coordinated by six oxygens. This structure can be understood to be constructed by triangular lattices of anions and honeycomb lattice of cations, stacking along the [111] axis of the rhombohedral unit cell. The axis will be denoted z or c axis in the following, referred to the hexagonal frame. The coordination octahedron in this crystal is not regular but distorted. The upper triangle of oxygen atoms coordinating to the uppermost cation in the figure, for example, is smaller than the lower triangle, whereas the situation is reversed for the lowermost cation. We will call the former cation site as [+] and the latter site as [-]. Because of this distortion, the crystalline field at the cation has the c component, + or -according to whether the site belongs to the [+] or [-] type. The [+] site is converted to the [-] site by inversion I. We can assume that the electric polarization exists at each cation sites, directed inversely for [+] and [-] sites. Below about 300 K, Cr2O3 is an antiferromagnet with the spins parallel to the c axis. The antiferromagnetic sublattices will be specifed by ↑ a n d ↓ . A s i t
doi:10.12693/aphyspola.81.431
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