A phase transition in NiF2 at elevated pressures

A pressure-induced phase transition occurs in NiF2 at room temperature from a tetragonal to an orthorhombic structure. To the limits of our x-ray dispersion (CuKα radiation, 114.6-mm camera), it may be second or first order and becomes resolvable at about 40 kbar. We suggest that it may be magnetic in origin but the Bloch 10/3 rule virtually precludes its identification with the low-temperature weakly ferromagnetic orthorhombic form. Another possibility is that it is strain induced via a soft mode and not magnetic in origin.