Magnetic phase diagram of CsNiF3

We study the phase diagram of CsNiF3, a quasi one-dimensional ferromagnet in the three-dimensional antiferromagnetically ordered phase (T<T-N). Due to an isotropic antiferromagnetic exchange interaction and the dipole-dipole interaction the system has a collinear ordered ground state. For homogeneous magnetic fields perpendicular to the spin chain axis we investigated the stability of the Neel and the paramagnetic phase. For fields along the spin direction the Neel phase is metastable up to a critical field, which depends solely on the dipolar energy. In addition we calculated the transition of the paramagnetic phase to an intermediate phase. Depending on the direction of the field the system undergoes a transition to a commensurate or an incommensurate phase. (C) 1997 American Institute of Physics.