The magnetoelastic effect in CoF2 investigated by means of neutron powder diffraction.

We have investigated the magnetoelastic effects in CoF(2) associated with the antiferromagnetic phase transition temperature T(N)≈39 K by means of neutron powder diffraction. The temperature variation of the lattice parameters and the unit cell volume has been determined accurately with small temperature steps. From the temperature variation of the lattice parameter c we extracted the lattice strain Δc associated with the antiferromagnetic phase transition. Rietveld refinement of the crystal and magnetic structure from the diffraction data at 2.2 K gave a magnetic moment of 2.57 ± 0.02 μ(B) per Co ion. We determined the temperature variation of the intensity of the 100 magnetic Bragg reflection, which is proportional to the square of the order parameter of the phase transition. We established that the lattice strain Δc couples linearly with the square of the order parameter of the antiferromagnetic phase transition in CoF(2).