BANDWIDTH CONTROL OF THE SPIN-DIFFUSION THROUGH INTERFACES AND THE ELECTRON-PHONON COUPLING IN MAGNETORESISTIVE MANGANITES

Electronic bandwidth in ferromagnetic manganese perovskites is known t o control several significant properties. In this paper we take advant age of this remarkable property to show that the interface scattering, leading to low-field magnetoresistivity (LFMR), and electron-phonon c oupling can be modified by using the appropriate chemical substitution s. The magnetoresistance and the magnetization of ceramic L2/3-xL'(x)A (1/3)MnO(3) (L,L' = lanthanides, A = Sr, Ca) oxides have been studied as a function of the grain size. It is found that these ceramics becom e magnetically harder when reducing the particle size and display a gr adual increase in low-field magnetoresistance. Narrowing the bandwidth reinforces these effects. We suggest that both phenomena could be clo sely related and associated with the existence of some degree of spin disorder at the grain boundaries. On the other hand, the dependence of the Curie temperature on hydrostatic pressure P for several samples h ave been determined. It is found that the Curie temperature, T-C, bein g itself a function of the electronic bandwidth W, displays a larger v ariation of d In T-C/dP as the bandwidth is reduced. However: the obse rved d In T-C/dP versus T-C or W variations are found to be significan tly larger than expected on the basis of simple steric modifications o f bandwidth. We suggest that the electron-phonon coupling is substanti ally reduced under pressure, this effect being more prominent as the b andwidth is reduced.