Enhanced magnetoresistance and Griffiths phase induced by Mo substitution in La0.7Ca0.15Sr0.15Mn1−xMoxO3 (0 ⩽ x ⩽ 0.05)

Abstract

Structural, magnetic and electrical properties of the La0.7Ca0.15Sr0.15Mn1−xMoxO3 (0 ⩽ x ⩽ 0.05) compounds have been investigated. Powder x-ray analysis reveals that the sample with x = 0 crystallizes in the rhombohedral structure, whereas in the Mo doped samples the structure can be indexed by an orthorhombic (Pbnm) structure. The important observations of the magnetic and transport properties are: (i) the Mo substitution induces a distinct suppression of the metal–insulator (TMI) and ferromagnetic (FM)—paramagnetic transition (TC) and the temperature of TMI was found to be higher than TC in the Mo-doped samples, (ii) the substitution of Mo enhances the magnetoresistance at room temperature, (iii) a large deviation from the Curie–Weiss law well above TC in the Mo substituted samples indicates the existence of a Griffiths phase and (iv) long-range FM order persists in all samples with a linear decrease of saturation moment as x increases. These results are discussed in terms of the Mn-site disorder and opening of strong FM coupling between Mn2+–O–Mn3+, due to the Mn2+ ions induced by Mo6+ at the expense of Mn4+ ions in the La0.7Ca0.15Sr0.15Mn1−xMoxO3 system.