First-order ferromagnetic transition in single-crystalline (Mn,Fe)(2)( P,Si)

(Mn,Fe)(2)(P, Si) single crystals have been grown by flux method. Single crystal X-ray diffraction demonstrates that Mn0.83Fe1.17P0.72Si0.28 crystallizes in a hexagonal Fe2P crystal structure (space group P (6) over bar 2m) at both 100 and 280 K, in the ferromagnetic and paramagnetic states, respectively. Magnetization measurements show that the crystals display a first-order ferromagnetic phase transition at their Curie temperature (T-C). The preferred magnetization direction is along the c axis. A weak magnetic anisotropy of K-1 = 0.28 x 10(6) J/m(3) and K-2 = 0.22 x 10(6) J/m(3) is found at 5K. A series of discontinuous magnetization jumps is observed far below TC by increasing the field at constant temperature. These magnetization jumps are irreversible, occur spontaneously at a constant temperature and magnetic field, but can be restored by cycling across the first-order phase transition.