Disorder and Doubleexchange Spin Dynamics in La0'7Sr0'3MnO3 and La0'7Sr0'3CoO3 from NMR Hyperfine Co

1
Disorder and Double-exchange Spin Dynamics in
La0.7Sr0.3MnO3 and La0.7Sr0.3CoO3 from NMR
Hyperfine CouplingsM.J.R. Hoch1, P.L. Kuhns1,
W.G. Moulton1, A.P. Reyes1, M.A. Torija2, J.F.
Mitchell3 and C. Leighton2
Phys. Rev. B 75, 104421 (2007)

• 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 (x0.3) 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.

Figure 1. Log-log plot og spin-lattice
relaxation rates versus ?Tfor x0.3 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) x0.3 LSMO, and (b) x0.3 LSCO.
1 National 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