  It has been observed that in bulk and polycrystalline thin films of collossal
magnetoresistive (CMR) materials the magnetoresistance follows a different
behaviour compared to single crystals or single crystalline films below the
ferromagnetic transition temperature Tc. In this paper we develop a
phenomenological model to explain the magnetic field dependence of resistance
in granular CMR materials taking into account the spin polarised tunnelling at
the grain boundaries. The model has been fitted to two systems, namely,
La0.55Ho0.15Sr0.3MnO3 and La1.8Y0.5Ca0.7Mn2O7. From the fitted result we have
separated out, in La0.55Ho0.15Sr0.3MnO3, the intrinsic contribution from the
intergranular contribution to the magnetoresistance coming from spin polarised
tunnelling at the grain boundaries. It is observed that the temperature
dependence of the intrinsic contribution to the magnetoresistance in
La0.55Ho0.15Sr0.3MnO3 follows the prediction of double exchange model for all
values of field.
