The coexistence of magnetic phases at the first-order phase transition of a metamagnet FeCl₂·2H₂O studied by x-ray diffraction

The results of non-resonant magnetic x-ray diffraction measurements of the metamagnet FeCl₂·2H₂O subjected to an applied magnetic field, H, are reported. The material shows two successive first-order phase transitions: at H_c1 = 3.62 T from the antiferromagnetic (AF) to intermediate (I) phases, and at H_c2 = 4.67 T from phase I to a ferromagnetic phase at low temperatures. We find that the AF and I phases coexist over a wide range of H below H_c1, when H is decreased from the I phase. We were able to follow the evolution of the AF and I domains with the change of H. The coexistence appears not to come from demagnetizing effects, and instead reflects the intrinsic nature of the material.