Vibronic superexchange in single-crystal LaMn1-xGaxO3 - art. no. 184423

The temperature dependence of the thermal conductivity, low-field/high-fiel d magnetization, and magnetic ac susceptibility under different hydrostatic pressures have been measured on single-crystal samples of LaMn1-xGaxO3. Th e data reveal a spin-glass phase in low magnetic fields and a ferromagnetic phase in high fields H greater than or equal to2 kOe. Orbital fluctuations suppress the phonon component and the spin-glass phase suppresses the spin -wave component of the thermal conductivity kappa (T); the x = 0.5 sample h as a kappa (T) like that of a glass insulator. On the other hand, pressure stabilizes long-range antiferromagnetic order. The data demonstrate a compe tition between magnetic and elastic energies; in the x = 0.5 sample, region s with three-dimensional orbital fluctuations and ferromagnetic (180 degree s - phi) Mn(III)-O-Mn(III) vibronic superexchange interactions coexist with regions in which orbital ordering gives rise to an antiferromagnetic inter action between (001) planes.