Resonant x-ray magnetoelectric effect in a centrosymmetric spinel oxide

We show clear evidence that the local magnetoelectric (ME) effect arising from the noncentrosymmetric magnetic sites can be element-specifically detected by using the resonant x-ray ME scattering (XMES), even in systems where the space-inversion $(I)$ or the time-reversal $(R)$ symmetry is globally restored. At the (222) reflection in a centrosymmetric spinel oxide MnCr₂O₄, where the conventional Mn-resonant x-ray magnetic scattering is forbidden, we have observed a resonant magnetic signal at the intra-atomic 1s-3d absorption edge of Mn ions on tetrahedral sites, which is uniquely attributed to the XMES. This unique x-ray scattering is caused by a transfer of the spectral weight between the electric dipole $(E1)$ and electric quadrupole $(E2)$ transitions through the spin-orbit coupling. The possibility of the important application utilizing the ME scattering technique is discussed as well.