Study of the colossal magnetoresistance properties of the compound La(1-x)Sr(x)A(y)Mn(1-y)O(3) (A = Cr, Re)

We report on the variation of the magnetoresistance property of La1-xSrxMnO 3 whose Mn sites are doped with chromium and rhenium. Two different series of compounds of the formula La0.7Sr0.3CryMn1-yO3 (y = 0.05, 0.10, 0.15, 0.2 0, 0.30, 0.40 and 0.50) and La1-xSrxRe0.10Mn0.90O3 (x = 0.12, 0.20 and 0.30 ) are prepared. A detailed study has been carried out to determine the stru ctural, magnetic and transport properties of the chromium and rhenium doped compounds using the x-ray diffraction, de magnetic susceptibility, four pr obe method for electrical resistance and magnetoresistance measurement tech niques. X-ray diffraction shows the formation of a homogeneous compound wit h the rhombohedral (R - 3c space group) structure within the Cr concentrati on of 0.05 < y < 0.15 for the La0.7Sr0.3CryMn1-yO3 and 0.12 < x < 0.30 for the La1-xSrxRe0.10Mn0.90O3 compounds. The magnetization, magnetic transitio n temperature and the metal-insulator transition temperature decrease due t o the Cr (Re) substitution. The magnetization curves broaden and the overal l resistivity of the compounds increases with increasing Cr or decreasing S r content except for the La0.88Sr0.12Re0.10Mn0.90O3 compound, whose resisti vity decreases and which shows metallic behaviour below the transition temp erature. The resistivity and the magnetization show a scaling dependence on each other. It is shown that the variation in the magnetic and transport p roperties of the substituted compounds can be ascribed to a compositional d ependence of the Mn3+-Mn4+ ferromagnetic interaction as a result of the ant iferromagnetic interaction of Cr3+-O-Cr3+ ions and to the distortion of the crystal lattice. The magnetoresistance shows an increasing trend due to th e increased resistivity of the compounds and is explained on the basis of p ercolation of the charge carriers through the ferromagnetic clusters presen t in the insulating antiferromagetic compounds and scattering effect at the grain boundaries.