On the strength of the double exchange and superexchange interactions in La0.67Ca0.33Mn1-yFeyO3 - an NMR and Mossbauer study

A combined study of (La0.67Ca0.33Mn0.97Fe0.03O3)-Fe-57 compound by means of zero field Mn-55 and Fe-17 NMR as well as Fe-57 Mossbauer spectroscopy (MS) is reported. The Mn-55 NMR spectra exhibit a single double exchange (DE) line up to the magnetic ordering temperature (T-C), 200 K, determined from magnetization measurements. The hyperfine field (HFF) remains finite at the T-C, which reveals discontinuous character of the transition and the occurrence of a ferromagnetic-paramagnetic phase segregation. The Fe-57 MS HFF decreases much faster with increasing temperature than the Mn-55 NMR HFF. Application of a molecular field model to the temperature dependence of the Mn-55 and Fe-57 HFF allows to estimate values of the Mn-Mn and the Fe-Mn exchange integrals, which amount to 1.24 meV and -0.6 meV, respectively. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.