ESR and magnetization in Jahn-Teller-distorted LaMnO3+delta: Correlation with crystal structure

We present magnetic susceptibility, x-ray-diffraction, and electron-spin-re sonance (ESR) studies in the series of nonstoichiometric compounds LaMnO3+d elta, for 0 less than or equal to delta less than or equal to 0.07. The mea surements were performed in the paramagnetic regime, especially near the te mperature T-JT for the Jahn-Teller transition observed in these samples. We observed important anomalies in both X-dc(T) and ESR linewidth Delta H-pp( T) near T-JT, Which was found dependent on delta. We explain these observat ions considering the crucial role of the lattice distortions which strongly affect the magnetic interactions. For the ESR spectra we assume a spin Ham iltonian including single-ion crystal-field interaction as well as isotropi c 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 depen dent. We have been able to reproduce the behavior of X-dc(delta,T) and Delt a H-pp(delta,T), including the anomalies at approximate to T-JT,T- with a s imple model where the T dependence of the exchange constants and of the cry stal-field interaction are proportional to the orthorhombic strain. By cont rast, the DM coefficient is constant for all delta and T and would depend o nly on the tilting of the MnO6 octahedra which is approximately the same fo r all the samples studied. A structural and magnetic phase-diagram T versus delta also discussed.