Flat and conical incommensurate magnetic structures in the two-subsystem partially frustrated Heisenberg ferrimagnet

The phase transitions into flat and conical incommensurate magnetic structures are considered for a ferrimagnet with the dominant nonfrustrated exchange between the spins in one crystallographic position, competing exchanges between the spins in another position and frustrated exchange between the spins in different positions. The appearance conditions and the temperatures of the second order phase transitions are analytically obtained in the mean field approximation. The first order phase transition between these states is studied and the phase diagrams of temperature vs frustrated exchanges are calculated by the numerical minimization of free energy. •3D spatial distribution of the spins decreases the energy of the frustrated exchanges.•Symmetry of the antiferromagnetic conical structure reduces the number of variables.•The collinearity of the spins and the local fields gives a simple analytical solution.