Observation of field-induced magnetic and structural transitions in an antiferromagnet by means of synchrotron x-rays

In the first experiment of its kind, we have used x-ray diffraction to study magnetic and charge properties of an antiferromagnet as a function of an applied magnetic field H. The intensity of hard x-rays diffracted at the space-group-forbidden reflection (3,0,0) of MnF2 with H parallel to the easy axis at H=H-c/root2 shows evidence of a spin-flop transition associated with the surface magnetization, and at H-c=9.3 T a spin-flop transition in the bulk. Above H, we found intensity much larger than that predicted for purely magnetic scattering. We attribute the unexpected intensity to charge scattering created by a field-induced structural phase transition.