Magnetoelectric Effect and Spin Direction in a Spin Flopped Cr₂O₃ Single Crystal

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Magnetoelectric susceptibilities α₃₃ and α₂₃ of an antiferromagnetic Cr₂O₃ single crystal have been measured in a pulsed magnetic field up to about 100 kOe. Here the 1-, 2- and 3-axes are along the binary axis, in the glide plane and along the trigonal axis, respectively. Both α₃₃ and α₂₃ have a finite value after a spin flop transition in the range from liquid helium temperature to room temperature. This result leads to the conclusion that the magnetic point symmetry of spin flopped Cr₂O₃ is 2⁄m′ or 1′. The compatible spin direction in the basal plane must have a component normal to the binary axis.