Bandwidth control of the spin diffusion through interfaces and the electron-phonon coupling in magnetoresistive manganites

Electronic bandwidth in ferromagnetic manganese perovskites is known to control several significant properties. In this paper we take advantage of this remarkable property to show that the interface scattering, leading to low-field magnetoresistivity (LFMR), and electron-phonon coupling can be modified by using the appropriate chemical substitutions. 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 become magnetically harder when reducing the particle size and display a gradual increase in low-field magnetoresistance. Narrowing the bandwidth reinforces these effects. We suggest that both phenomena could be closely 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 have been determined. It is found that the Curie temperature, T-C, being itself a function of the electronic bandwidth W, displays a larger variation of d In T-C/dP as the bandwidth is reduced. However: the observed d In T-C/dP versus T-C or W variations are found to be significantly larger than expected on the basis of simple steric modifications of bandwidth. We suggest that the electron-phonon coupling is substantially reduced under pressure, this effect being more prominent as the bandwidth is reduced.