Neutron scattering study of two-dimensional randomly mixed magnets with competing anisotropies K2Cu1-xCoxFe4

The random mixture of a quasi-two-dimensional magnet of K2Cu1-xCoxF4 is studied by neutron scattering in the ferromagnetic composition range, 0.2 > x > 0. K2CuF4 is the XY-like ferromagnet with the distorted K2NiF4-type structure. The substitution of Ising spins of Co for XY-like spins of Cu by a few percent brings about a rotation of the easy axis. Two critical lines of three-dimensional XY and two-dimensional Ising characters, intersecting at a tetracritical point, are observed as is commonly seen in randomly mixed magnets with orthogonal anisotropies. It was also found that K2Cu1-xCoxF4 with 0.2 > x > 0.05 is a model system of the two-dimensional Ising ferromagnet. (author)