Inelastic neutron scattering was employed to study the magnetic excitations of Mn${}^{3+}$ dimers in LaMn${}_{0.1}$Ga${}_{0.9}$O${}_3$. The nearest-neighbor interaction of Mn${}^{3+}$ ions is ferromagnetic in the basal (a-b) plane, but antiferromagnetic along the $c$ direction; thus two different types of dimer excitations are simultaneously present in the experiments. From the observed energy spectra we derive Heisenberg-type exchange interactions $J_{\mathit{ab}}$ $=$ 0.210(4) meV and $J_c$ $=$ –0.285(5) meV as well as an axial anisotropy parameter $D$ $=$ 0.036(6) meV. These parameters differ considerably from those derived for the isostructural parent compound LaMnO${}_3$ due to structural effects.

• Received 16 March 2011

DOI:https://doi.org/10.1103/PhysRevB.83.174442