Paramagnetic resonance of Mn$^{4+}$ and Mn$^{2+}$ centers in lanthanum gallate single crystals

An increase in the manganese concentration in lanthanum gallate in the range 0.5–5.0% has been found to result in a complete replacement of individual Mn$^{4+}$ ions by Mn$^{2+}$ ions. The relative concentrations and binding energies of individual Mn$^{4+}$, Mn$^{3+}$, and Mn$^{2+}$ ions have been determined. The spin Hamiltonians of the Mn$^{2+}$ and Mn$^{4+}$ centers in the rhombohedral and orthorhombic phases, respectively, have been constructed and the orientation of the principal axes of the fine-structure tensor of Mn$^{4+}$ at room temperature has been found. The possibility of using electron paramagnetic resonance for determining the rotation angles of oxygen octahedra of lanthanum gallate with respect to the perovskite structure has been discussed.