Magnetic properties and magnetoresistance of Bi and Fe substituted manganites

In this work structure, magnetic and transport properties of La-0.7 (\) Bi\Ca0.3MnO3 (0.05 less than or equal to x less than or equal to 0.7). La0.7Pb0.3Mn1-x-Fe\O3 and La0.7Sr0.3Mn1-xFeO3 (0 less than or equal to x less than or equal to 0.3) manganites have been studied. Competition between ferromagnetic and antiferromagnetic interactions has been observed giving rise to complex magnetic behaviour, including metamagnetism and spin glass features. Such features art: interpreted as arising from the weakening of the double exchange mechanism, of ferromagnetic character. as a consequence of the substitutions. In the case of Bi substituted compounds the covalent character of Si strongly localizes the hopping electron. while the Fe substitution destroys the double exchange mechanism by the change in energy levels of the Fe4+ ions with respect to the Mn4+ ones.