Magneto-electric optics in non-centrosymmetric ferromagnets

Non-centrosymmetric ferromagnetic materials can show optical and x-ray responses unique to magneto-electrics. For example, the refractive index and absorption coefficient may be dependent on the directions of light (x-ray) propagation k and magnetization 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 in GaFeO(3) and CuB(2)O(4). The ME optics can be explained from the microscopic point of view by the interference of an electric dipole (E1) process with a magnetic dipole (M1) or electric quadrupole (E2) process at non-centrosymmetric magnetic sites. Even in magnetic crystals with global inversion symmetry, 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 in GaFeO3 and Fe(3)O(4). Artificial breaking of space inversion by means of currently used techniques such as lithography can be applied to the exploration of multiferroics, as a way of investigating ME optics. Relatively large ME optical signals at room temperature have been successfully observed in diffraction from such tailor-made multiferroics.