| In recent years, the colossal magneto-resistance effect in rare-earth manganite perovskites of the type Lni.xAxMnO3(where Ln is rear-earth irons La2+, Nd2+, P2+; A is alkaline earth iron Ca2+, Sr2+, Ba2+) has attract considerable attention in scientific studies due to its potential application.However, the poor temperature dependence of MR and the low-temperature MR effect and the ideal MR only in high field severely limit their practical utility.In this work, we prepared manganite perovskite Lai-xSrxMnO3 and soft-magnetic ferrite materials Fe2O3 and (Ni,Zn)Fe2O4 by using sol-gel method separately. Then, using second doping method, we compound the soft-magnetic ferrite into Lai-xSrxMnO3. After fully mixing, the compounds were pressed into pellets and sintered under different temperatures. And then, we get the final hetero-structure samples.There are several interesting results we have got:1. The XRD patterns of composite sample between Lai.xSrxMnO3 and (Ni,Zn)Fe2O4 showed that the two matters existed in themselves phase, and there was no reaction between them at all.2. There is an obviously increase on the resistivity of the composite sample doped with the increasing of the (Ni,Zn)Fe2O4 content, which can be due to the following two reasons: (1) The grain size of ferrite is much larger than one of Lao.?Sro sMnOs . After we doped the LaojSro MnO with ferrite (Ni,Zn)Fe2O4, a lot of hetero-grain-boundary were produced, which enhance the disorder scattering of electron; (2) the ferrite introduced into the Lao 7Sro3MnO3 is an insulator itself, whose resistivity has important influence on the whole resistivity of the composite system.3. For the composite system of Lai-xSrxMnO3 and (Ni,Zn)Fe2O.4, an enhancement effect of the magneto-resistance at low temperature was observed. We found that the MR value of the sample diluted with (Ni,Zn)Fe2O4 surpass the ones of the sample without (Ni,Zn)Fe2O4 in the vicinity of 220K.4. When we doped the Lao Sro iMnO3 with soft-magnetic ferrite Fe2O3, an interesting result was observed. At low temperature, magneto-resistance is very small. With the increasing of temperature, it took on a negative MR effect(where we definite MR = (p0 - pH)/p0), which is different with the usual materials. For the sample with the content of Fe2O3 is 9%, the maximum MR value of the composition (Lao9SroiMnO3)o9i( Fe2O3)oo9 increased in the negative direction, and get the maximum -7% at 337K; with the content of FeiO increased, the MR of the composition increased also, When the content of Fe2O3 is 17%, the maximum MR value of the composition (Lao.gSro iMnO3)o.83( FeiO o.n can reach -30% at 338K, where applied magnetic field is 1.5T.5. Though the two doped materials in the composition system are all soft-magnetic ferrite, but the results are very different. In the Lao SrojMn03 /(Ni,Zn)Fe2O4 system, the size of the two materials are all in the range of micro-meter; but in the LaogSro iMnO3 Fe2O3 system, the diameter of the FejCh are only several tens of nanometers. As a consequence, we regard that the size of the samples is an important factor which affect the MR response of the system. |
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