"Inhomogeneity in the Spin Channel of Ferromagnetic CMR Manganites"

Relatore: R. H. Heffner
Los Alamos National Laboratory

Aula Newton 
21 Gennaio 2002 - Ore 16.30


Colossal magnetoresistance materials are archetypes in which
 to study the effects of strong coupling between the spin, 
charge and lattice degrees of freedom in materials. 
 These effects include formation of spin-lattice polarons,
 charge and orbital ordering, extreme sensitivity to 
applied magnetic fields and inhomogeneous spin dynamics.
   The muon spin relaxation (SR) technique provides a
 powerful local magnetic probe with which to investigate 
the spin degrees of freedom in these materials. 
 A survey of the zero-field magnetic properties
 of the series La1-xCaxMnO3 using SR will 
presented, with particular emphasis on the
 ferromagnetic ground state materials.
  It is found that there are several
 characteristic relaxation modes which 
are produced as a direct result of the 
strong spin-charge-lattice interaction. 
 Results from inelastic neutron spin echo
 scattering, which directly measures the spin-spin
 correlation function, will also be presented and 
compared to the SR data.  A qualitative model 
for the ferromagnetic transition in the 
manganites suggested by these data will be discussed.