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1 National High Magnetic Field Laboratory, FSU, Tallahassee, FL

The magnetic oxides La 1-x Sr x MnO 3 (LSMO) and La 1-x Sr x CoO 3 (LSCO) have interesting and unusual properties, including very large magnetoresistance, that pose challenges to our understanding and opportunities for application in technology.

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1 National High Magnetic Field Laboratory, FSU, Tallahassee, FL

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  1. The magnetic oxides La1-x Srx MnO3 (LSMO) and La1-x Srx CoO3 (LSCO) have interesting and unusual properties, including very large magnetoresistance, that pose challenges to our understanding and opportunities for application in technology. Changing Mn (LSMO) to Co (LSCO) results in striking changes in behavior and the present work has investigated samples of the two materials in their ferromagnetic-metallic phases (x=0.3) in an effort to deepen our understanding of the competing interactions that determine the properties. Using pulsed NMR information on the electron spin system has been obtained that shows that at low temperatures lattice disorder effects linked to Jahn-Teller distortion of the octahedral environment of the transition ions are more important in LSCO than in LSMO. This difference is attributed to the stronger double-exchange interaction in LSMO than in LSCO. Above 120 K, well below the Curie temperature of 360 K, lattice distortions are shown to ‘kick in’ in LSMO. These effects can lead to localization of the electrons and the formation of spin polarons. The three plots compare the results obtained for the two systems and show strikingly different behavior that is analyzed to obtain information on the roles of the underlying interactions. Disorder and Double-exchange Spin Dynamics in La0.7Sr0.3MnO3and La0.7Sr0.3CoO3from NMR Hyperfine CouplingsM.J.R. Hoch1, P.L. Kuhns1, W.G. Moulton1, A.P. Reyes1, M.A. Torija2, J.F. Mitchell3 and C. Leighton2Phys. Rev. B 75, 104421 (2007) Figure 1. Log-log plot og spin-lattice relaxation rates versus Tfor x=0.3 LMSO and LSCO. The insert shows the importance of spin waves on LSMO below 100 K. (a) (b) Figure 2. Linewidths and relaxation rates Versus T for (a) x=0.3 LSMO, and (b) x=0.3 LSCO. 1National High Magnetic Field Laboratory, FSU, Tallahassee, FL 2 Dept of Chemical Engineering and Materials Science, University of Minnesota, MN 3 Materials Science Division, Argonne National Laboratory, Argonne, IL

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