Abstract
Non-centrosymmetric ferromagnetic materials can show optical and x-ray responsesunique to magneto-electrics. For example, the refractive index and absorptioncoefficient may be dependent on the directions of light (x-ray) propagationk andmagnetization M, and these dependences can be termed directional birefringence and directional dichroism,respectively. Such a kind of magneto-electric (ME) optics has recently been observed inGaFeO3 and CuB2O4. The ME optics can be explained from the microscopic point of view by the interference ofan electric dipole (E1) process with a magnetic dipole (M1) or electric quadrupole (E2) processat non-centrosymmetric magnetic sites. Even in magnetic crystals with global inversionsymmetry, the E1–E2 interference can occur at magnetic sites with local inversion breaking,causing unique x-ray diffraction. Such ME-effect-related x-ray diffraction has been found inGaFeO3 and Fe3O4. Artificial breaking of space inversion by means of currently used techniques suchas lithography can be applied to the exploration of multiferroics, as a way ofinvestigating ME optics. Relatively large ME optical signals at room temperaturehave been successfully observed in diffraction from such tailor-made multiferroics.
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