Metal-insulator transition in La0.7Sr0.3Mn1-xFexO3

We report the effect of Fe doping at the Mn site in La0.7Sr0.3MnO3 oxides. We find that the doping of Fe does not cause any structural change, but the electrical transport in the system is strongly affected. The parent compound La0.7Sr0.3MnO3 shows a resistivity peak at T=T-p (365 K) and behaves as a ferromagnetic metal at low temperature. Double exchange (DE) interaction between Mn3+ and Mn4+ is understood to be the cause of ferromagnetism and metallicity of the material. As Fe is doped into the system a depletion in the number of hopping electrons occurs and consequently the DE interaction becomes weak, however, as long as x less than or equal to 0.2 the system shows metallic behavior at low temperatures. For higher Fe doping the system becomes insulating throughout the whole temperature range. Electron tunneling conductance measurements show that the density of states of metallic samples exhibits a dip at E-F. As the value of x increases the dip deepens and finally at x=0.25 a gap opens up at the Fermi level. (C) 1999 American Institute of Physics. [S0021-8979(99)10020-3].