AC Susceptibility Studies in Fe doped La0.65Ca0.35Mn1-xFexO3: Rare Earth Manganites

TL;DR

This study investigates how Fe doping affects the magnetic and electrical properties of La0.65Ca0.35MnO3, revealing a transition from metallic to insulating ferromagnetism and complex ac susceptibility behavior due to magnetic clustering.

Contribution

It provides detailed insights into the effects of Fe substitution on magnetic transitions, susceptibility, and spin disorder in La0.65Ca0.35MnO3, highlighting the formation of magnetic clusters and their impact.

Findings

Fe doping broadens the CMR temperature range.

Transition from metallic ferromagnet to ferromagnetic insulator with increased Fe.

Double bump in ac susceptibility's out-of-phase component observed at low Fe concentrations.

Abstract

The effect of Fe substitution on Mn sites in the colossal magnetoresistive compounds La0.65Ca0.35Mn1-xFexO3 with 0.01<x<0.1 have been studied. A careful study in the magnetic properties has been carried out by the measurement of ac susceptibility. The temperature range of CMR is greatly broadened with the addition of Fe. Substitution of Fe induces a gradual transition from a metallic ferromagnetic with a high Curie temperature (Tc=270 K) to a ferromagnetic insulator with low Tc=79 K. Increased spin disorder and decrease of Tc with increasing Fe content are evident. The variations in the critical temperature Tc and magnetic moment show a rapid change at about 4-5% Fe. The effect of Fe is seen to be consistent with the disruption of the Mn-Mn exchange possibly due to the formation of magnetic clusters. An extra-ordinary behavior in the out of phase part (x") of ac susceptibility, characterized by double bump (shoulder), was observed around x=0.01 and 0.02. The shoulder in x" disappears at x>0.04 Fe concentration. With increasing Fe concentration the x" peak shift to T<T1/2 (mid point of the transition temperature) and becomes broader. The x" peak moves to 8 or 10 K higher temperature on the application of a dc field, for 3 & 4% samples. We also see increasing low temperature dissipation in more strongly Fe doped samples i.e. increasing the Fe, leads to increased spin disorder and dissipation at low temperature. The effect of the dc field is discussed in terms of the suppression of spin fluctuations close to Tc. The same ionic radii of Fe3+ and Mn3+ cause no structure changes in either series, yet ferromagnetism has been consistently suppressed by Fe doping. Doping with Fe bypasses the usually dominant lattice effects, but depopulate the hopping electrons and thus weakens the double exchange. The results were explained in terms of the formation of magnetic clusters of Fe ions.