PACS 75.85.+t -Magnetoelectric effects, multiferroics PACS 75.25.-j -Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.) PACS 75.10.-b -General theory and models of magnetic ordering Abstract -Single crystals of the orthorhombic polar oxide α-Cu2V2O7 with space group F dd2 are synthesized and their physical properties are measured. Neutron powder diffraction is also performed on a polycrystal sample to extract the magnetic structure. The ground state is shown to be weakly ferromagnetic, that is, collinearly antiferromagnetic in the a-direction with a small remanent magnetization in the c-direction. When an external magnetic field is applied in the c-direction, further spin canting, accompanied by the induced electric polarization, occurs. It is demonstrated that the magnetoelectric effect in α-Cu2V2O7 is adequately described if spindependent p-d hybridization due to spin-orbit coupling as well as magnetic domain effects are simultaneously taken into account. We discuss the implication of the present result in the search for materials with multiferroicity and/or magnetoelectricity.

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