Evidence for the persistence of weak ferromagnetism in mixed-spin magnetic systems on the body-centered octahedral lattice: An exact theoretical analysis

Prediction of weak ferromagnetism in mixed-spin 1/2−σ systems on the body-centered octahedral lattice, with the presence of atoms with higher spin values (up to σ=3) in the centers of all elementary octahedra of the lattice, is given using the recursive lattice technique. Exact solutions of all studied recursive systems are found, the corresponding phase diagrams are determined, the equations that drive the positions of all critical temperatures of the second-order phase transitions of the model for all studied spin values are derived, and the magnetization properties of the model are analyzed and discussed in detail. It is shown that, when the antiferromagnetic nature of the interactions between the nearest-neighbor vertices within all elementary octahedra is assumed, the presence of the weak ferromagnetic phases in the system, early observed within pure spin-1/2 model, is preserved for arbitrary studied higher spin values of the atoms placed in the centers of elementary octahedra, regardless of the ferromagnetic or antiferromagnetic character of the nearest-neighbor interactions between these central sites of the lattice and the spin-1/2 atoms placed at the vertices of the corresponding octahedra. It is shown that the higher spin values of the central sites of the lattice significantly change the region of model parameters where the weak ferromagnetism can be observed but the phenomenon itself cannot be suppressed by any value of σ. The obtained results within the given recursive-lattice approximation indicate that the nontrivial phenomenon of the weak ferromagnetism represents a natural intrinsic property of the wide class of magnetic systems with the basic octahedral structure. Moreover, it is also shown that, when all interactions in the mixed-spin model are antiferromagnetic, the compensation temperatures can always be observed in the corresponding weak ferromagnetic phases for suitable values of the ratio of two different interactions of the model.