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    STUDIA PHYSICA - Issue no. SPECIAL ISSUE / 2001  
         
  Article:   AN EPR INVESTIGATION OF GIANT MAGNETORESISTIVE PEROVSKITES DOPED WITH DIAMAGNETIC IONS.

Authors:  X. FILIP, N.M. GRECU, L.V. GIURGIU, A. DARABONT, O. RAITA, J. BLASCO.
 
       
         
  Abstract:  The effects of Mn site substitution by diamagnetic ions on the spin dynamics in the magnetoresistive La2/3Ca1/3Mn1-xDxO3 (D=Al, In; x  0.05) powders have been investigated by EPR. The temperature and x dependence of the resonance linewidth and integral intensity of the EPR signal have been investigated and discussed in terms of exchange narrowing and small polaron hopping model. In the paramagnetic regime, the exchange coupling integral,J,betweeen Mn3+ and Mn4+ ions shows a decrease with increasing x. It could arises from weakening of the double exchange interaction by D-doping which reduces the exchange field at the Mn sites.The activation energy, Ea, for the hopping motion of small polarons as function of x and D was evaluated and compared with the results of other experiments .  
         
     
         
         
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