ESR and magnetization in Jahn-Teller-distorted LaMnO31d : Correlation with crystal structure

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

PHYSICAL REVIEW B

AMER PHYSICAL SOC

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

1098-0121

We present magnetic susceptibility, x-ray-diffraction, and electron-spin-resonance ~ESR! studies in theseries of nonstoichiometric compounds LaMnO31d , for 0<d<0.07. The measurements were performed in theparamagnetic regime, especially near the temperature TJT for the Jahn-Teller transition observed in thesesamples. We observed important anomalies in both xdc(T) and ESR linewidth DHpp(T) near TJT , which wasfound dependent on d. We explain these observations considering the crucial role of the lattice distortionswhich strongly affect the magnetic interactions. For the ESR spectra we assume a spin Hamiltonian includingsingle-ion crystal-field interaction as well as isotropic and Dzyaloshinskii-Moriya ~DM! antisymmetric spinspinexchange. We found that the Curie-Weiss temperature and the high-T limit of the ESR linewidth, whichare usually constant parameters, are in this case temperature dependent. We have been able to reproduce thebehavior of xdc(d ,T) and DHpp(d ,T), including the anomalies at ´TJT , with a simple model where the Tdependence of the exchange constants and of the crystal-field interaction are proportional to the orthorhombicstrain. By contrast, the DM coefficient is constant for all d and T and would depend only on the tilting of theMnO6 octahedra which is approximately the same for all the samples studied. A structural and magneticphase-diagram T versus d is also discussed.