Interplay between magnetism and lattice distortions in LaMn 1 -xGaxO3

Abstract

A theoretical investigation of the structure, magnetism and thermal conductivity of LaMn1-xGaxO3 has been made. A local, cluster model is introduced. It is proposed that gallium substitution may cause neighbouring Mn3+ (3x2 - r2)/(3y 2 - r2) orbitals to transform into the 3z2 - r2 state. This unique idea is the basis of a successful description of the structure and magnetism of LaMn1-xGaxO3. The evolution of the crystal lattice parameters has been simulated; agreement with experimental data is excellent; changes in orthorhombic strain and cell volume are also well predicted. The behaviour of the magnetization has been successfully described by a spin-flipping model: over the entire range of doping, good qualitative consistency between simulation predictions and experimental data is observed. Ultimately, the aforementioned results indicate that lattice distortions alone may be responsible for the observed magnetic order in these manganites. Additionally, the thermal conductivity of LaMn 1-xGaxO3 has been analysed. The results are fitted with a kinetic model. It appears that thermal currents in LaMn 1-xGaxO3 may be limited by scattering of phonons from the structural changes near the Ga ions.