Effects of iron doping on the transport and magnetic behaviour in La0.65Ca0.35Mn1-yFeyO3

We report on the magnetic and transport measurements in an Fe-doped colossa l magnetoresistance compound (La0.65Ca0.35MnO3). Increased spin disorder an d a decrease of T-c with increasing Fe content are evident. We find that th e resistivity data above T-p fits better to a variable range hopping model and the localization length decreases with Fe content. The variations in th e critical temperature T-c, confinement length, magnetic moment and magneto resistance show a rapid change at about 4-5% Fe. The maximum magnetoresista nce is seen to increase consistently with the addition of Fe and increases up to 400% for 8% Fe. The effect of Fe is seen to be consistent with the di sruption of the Mn-Mn exchange, possibly due to the formation of magnetic c lusters.