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摘要
The effects of Fe substitution on Mn sites in the colossal magnetoresistive compounds La(0.65)Ca(0.35)Mn(1-x)FexO(3) with 0.00 <= x <= 0.10 have been studied. A careful study in the magnetic properties has been carried out by the measurement of magnetic ac susceptibility. The temperature range of colossal magnetoresistance (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 (T-c=270 K) to a ferromagnetic insulator with low T-c=79 K. Increased spin disorder and decrease of T-c with increasing Fe content are evident. The variations in the critical temperature T-c 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 extraordinary behavior in the out of phase part (chi '') of ac susceptibility, characterized by double bump (shoulder), was observed around x=0.01 and 0.02. The shoulder in chi '' disappears at x >= 0.04 Fe concentration. With increasing Fe concentration the chi '' peak shift to T < T-1/2 (mid point of the transition temperature) and becomes broader. The chi '' peak moves to 8 or 10 K higher temperature on the application of a dc field, for 3 and 4% Fe samples. We observed that increasing the Fe, leads to increased spin disorder and dissipation at low temperature. The effects of the dc field are discussed in terms of the suppression of spin fluctuations close to T-c. 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 depopulates the hopping electrons and thus weakens the double exchange. The results were explained in terms of the formation of magnetic clusters of Fe ions.
- 出版日期2010-12-1
