Suppression of charge-ordering and appearance of magnetoresistance in a spin-cluster glass manganite La_0.3Ca_0.7Mn_0.8Cr_0.2O₃

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• 作者：Sudyoadsuk ; T. ; Suryanarayanan ; R. ; Winotai ; P. ; Wenger ; L.E.
• 关键词：75.47.Gk ; 77.84 ; 75.60.Ej ; Electron doped manganites ; Spin-cluster glass ; Charge ordering ; Cr substitution ; Colossal mangetoresistance
• 刊名：Journal of Magnetism and Magnetic Materials
• 出版年：2004
• 期刊代码：31_03048853
• 类别：ph
• 出版时间：July, 2004
• 卷：278
• 期：1-2
• 页码：96-106
• 文件大小：426 K

摘要

The magnetic properties of electron-doped manganite La_0.3Ca_0.7MnO₃ and La_0.3Ca_0.7Mn_0.8Cr_0.2O₃ polycrystalline samples prepared by sol–gel technique have been investigated between 5 and 300K in magnetic fields ranging from 0 to 5T. The transition at 260K, attributed to charge ordering in La_0.3Ca_0.7MnO₃, is completely suppressed in the Cr-substituted sample while the onset of a magnetic remanence followed by the appearance of a magnetic irreversibility at lower temperatures is observed in both samples. These features indicate that ferromagnetic clusters coexist with either an antiferromagnetic phase for La_0.3Ca_0.7MnO₃ or a spin-cluster glass phase for La_0.3Ca_0.7Mn_0.8Cr_0.2O₃ at the lowest temperatures. The exponential temperature dependence of the resistivity for the Cr-substituted sample is consistent with the small polaron hopping model for 120K<T<300K, while the data are better described by Mott's hopping mechanism for T<120K. Whereas the parent compound La_0.3Ca_0.7MnO₃ is known to show no magnetoresistance, a large negative magnetoresistance is observed in the La_0.3Ca_0.7Mn_0.8Cr_0.2O₃ sample below 120K. The appearance of the CMR is attributed to spin dependent hopping between spin clusters and/or between ferromagnetic domains.