ESR and magnetization in Jahn-Teller-distorted LaMnO 3 + δ :  Correlation with crystal structure

TOVAR, M.; ALEJANDRO, G.; BUTERA, A.; CANEIRO, A.; CAUSA, M. T.; PRADO, F.; SÁNCHEZ, R. D.

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

APS

Lugar: NY; Año: 1999 vol. 60 p. 10199 - 10205

0163-1829

We present magnetic susceptibility, x-ray-diffraction, and electron-spin-resonance (ESR) studies in the series of nonstoichiometric compounds LaMnO3+δ, for 0<~δ<~0.07. The measurements were performed in the paramagnetic regime, especially near the temperature TJT for the Jahn-Teller transition observed in these samples. We observed important anomalies in both χdc(T) and ESR linewidth ΔHpp(T) near TJT, which was found dependent on δ. We explain these observations considering the crucial role of the lattice distortions which strongly affect the magnetic interactions. For the ESR spectra we assume a spin Hamiltonian including single-ion crystal-field interaction as well as isotropic and Dzyaloshinskii-Moriya (DM) antisymmetric spin-spin exchange. We found that the Curie-Weiss temperature and the high-T limit of the ESR linewidth, which are usually constant parameters, are in this case temperature dependent. We have been able to reproduce the behavior of χdc(δ,T) and ΔHpp(δ,T), including the anomalies at ≈TJT, with a simple model where the T dependence of the exchange constants and of the crystal-field interaction are proportional to the orthorhombic strain. By contrast, the DM coefficient is constant for all δ and T and would depend only on the tilting of the MnO6 octahedra which is approximately the same for all the samples studied. A structural and magnetic phase-diagram T versus δ is also discussed.