共查询到17条相似文献,搜索用时 203 毫秒
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在2—390K温度之间研究了La0.8Ba0.2MnO3的 磁矩、磁电阻与温度的关系.发 现以不同价态的Mn元素引入得到的La0.8Ba0.2MnO3 ,性能虽然都存在金属 —绝缘体转变,以及在磁场作用下居里温度附近电阻率变化非常显著的特点,但是价态对磁 性转变温度TC,金属—绝缘体转变温度Tmi,以及磁电阻极大 值温度TMR的影 响都非常显著.三种价态相比较,使用二价Mn的电阻率最低以及磁性转变温度更接近室温.认 为影响材料性能的主要因素是材料制备时引进的Mn元素的价态,由于原料价态的不同而形成 的氧空位浓度变化,进而影响了Mn4+/Mn3+的比.
关键词:
价态
磁电阻
居里温度
金属—绝缘体转变 相似文献
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研究了溶胶-凝胶法制备氧化物巨磁电阻材料的工艺,制备了La0.7Sr0.3< /sub>CrxMn1-xO3(x=0,0.10,0.15)和La0.7Sr0.3FexMn1-xO3(x=0.05,0.10,0.16)两 系列的单相钙钛矿锰氧化物多晶样品,并研究了Cr,Fe替代La0.7Sr0.3 sub>MnO3中部分Mn后对其结构、磁性和巨磁电阻性质的影响.观察到La0.7 Sr0.3Cr0.15Mn0.85O3和La0. 7Sr0.3Fe0.05Mn0.95O3两个样品的 电阻-温度曲线都出现了双峰.定性讨论了可能产生双峰的机制.随Cr(或Fe)替代量的增加, 材料的居里温度很快下降,铁磁性减弱,导电性降低,巨磁电阻效应增强.但与Fe掺杂相比 ,相同数量的Cr掺杂对材料的影响要小.
关键词:
巨磁电阻效应
溶胶-凝胶工艺
电阻-温度曲线
金属绝缘体转变 相似文献
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在成功制备具有双钙钛矿结构Sr2Fe1-xCoxMoO6系列样品的基础上,对其结构、输运性质和磁性质进行了系统研究.结果发现,随着Co替代浓度x值的增加,样品的电阻率-温度关系由半金属行为转变为半导体行为,其室温电阻率从3.9×10-5Ω·cm增大到6.0×10-1Ω·cm;样品由亚铁磁体转变成反铁磁体,其磁相变温度TN值也随之下降; Co对Fe的部分替代使其磁电阻效应受到抑制.基于对其电子结构的分析,其磁电阻效应的起源以及Co的元素替代效应也在文中进行了讨论.
关键词:
双钙钛矿结构
2FeMoO6')" href="#">Sr2FeMoO6
磁电阻 相似文献
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采用高温固相法制备了Ba9(Y2-xScx)(SiO4)6:Ce3+,Mn2+(x=0,0.5,1.0,1.5,2.0)样品。在该体系中,当Sc3+含量从x=0逐渐增加至x=2时,Ce3+的蓝光发射强度提高了1.7倍;同时,Mn2+的红光发射强度提高了1.9倍,显示了优良的红光特性。样品的发射光谱和漫反射光谱表明,Ce3+、Mn2+发射强度的增加与Ce3+吸收能力和Ce3+向Mn2+能量传递的提升有直接关系。研究了样品Ba9Sc2(SiO4)6:Ce3+,Mn2+的热稳定性。随着温度的升高,Mn2+的红光发射呈现先升后降的态势。当温度从室温升至488 K时,Mn2+发射强度仅下降至室温时的84%,表现出优良的热稳定性。高亮的红光发射和优良的热稳定性表明该荧光材料可为紫外基白光LED提供良好的红色光源。 相似文献
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研究了钙钛矿型锰氧化物La2/3Ca1/3Mn1-xTixO3(0≤x≤0.3)的结构、磁性和输运性质.发现Ti替代Mn强烈地抑制了La2/3Ca1/3MnO3的铁磁性和金属电导,并很大地提高了磁电阻值.在低掺杂情况下(x≤0.04),1%的Mn被Ti替代,居里温度TC和金属-绝缘体转变温度Tp分别平均下降了31和26.5K.当x=0.06时,铁磁态过渡为团簇玻璃态,并在x=0.20时完全变为自旋玻璃态.指出由于Ti的掺入而引起的磁稀释作用以及局域晶格畸变是产生上述结果的主要原因.
关键词: 相似文献
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J.C. Debnath R. ZengJ.H. Kim S.X. Dou 《Journal of magnetism and magnetic materials》2011,323(1):138-143
The influence of first and second order magnetic phase transitions on the magnetocaloric effect (MCE) and refrigerant capacity or relative cooling power (RCP) of La0.7Ca0.3MnO3 and La0.7Ca0.3Mn0.95Co0.05O3 materials has been investigated. Large low-field-induced magnetic entropy changes are observed in La0.7Ca0.3MnO3 and La0.7Ca0.3Mn0.95Co0.05O3 materials. The La0.7Ca0.3MnO3 material experiences a large entropy change with a first-order magnetic phase transition at the Curie temperature, TC. On the other hand, La0.7Ca0.3Mn0.95Co0.05O3 displays a smaller entropy change with a second order phase transition. While a first-order magnetic transition material induces a larger MCE (7.528 J/kg K at 5 T) at TC, this is limited to a narrow temperature range, resulting in a relatively small RCP (218 J/kg), while the Co-doped second-order magnetic transition material induces a smaller MCE (7.14 J/kg K for 5 T), but it is spread over a broader temperature range, resulting in a larger RCP (308 J/kg). The maximum magnetoresistance (MR, defined as ρ(0)/ρ(H)-1) under a field of 5 T is about 206% and 333% for La0.7Ca0.3MnO3 and La0.7Ca0.3Mn0.95Co0.05O3, respectively. The refrigeration capacity (RCP) is enhanced in La0.7Ca0.3Mn0.95Co0.05O3 (by about 41%) due to small changes from Co doping. The magnetocaloric features of these materials at lower magnetic fields (MCE=3.163 for La0.7Ca0.3Mn0.95Co0.05O3 and 4.63 J/kg K for La0.7Ca0.3MnO3 at 1 T), and the high RCP and MR can provide some ideas for exploring novel magnetic refrigerants that can operate with permanent magnets rather than superconducting ones as the magnetic field source. 相似文献
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T.D. ThanhP.T. Phong N.V. DaiD.H. Manh N.V. KhiemL.V. Hong N.X. Phuc 《Journal of magnetism and magnetic materials》2011,323(1):179-184
We report magneto-transport and magnetic properties of (1-x)La0.7Ca0.3MnO3+xAl2O3 composites synthesized through a solid-state reaction method combined with a high energy milling method. Most interestingly, the effective magnetic anisotropy is found to decrease with increase in the non-magnetic insulating Al2O3 phase fraction in the composites. In addition, we observed that the magnitude of low-field magnetoresistance arising from spin-polarized tunneling of conduction electrons, as well as that of high-field magnetoresistance, displays a Curie-Weiss law-like behavior. Finally, we found that the temperature dependence of low and high-field magnetoresistance is controlled predominantly by the nature of temperature response of surface magnetization of the particles. 相似文献
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Simultaneous observation of positive and negative giant magnetoresistances in composite (La0.83Sr0.17MnO3)1-x(ITO)x 下载免费PDF全文
We have studied the transport property of the composites (La0.83Sr0.17 MnO3)1-x(ITO)x [ITO=(In2O3)0.95 (SNO2)0.05], which were fabricated by mechanically mixing La0.83Sr0.17MnO3 and ITO grains. A giant positive magnetoresistance (PMR) has been observed above the Curie temperature Tc for samples with x around 0.40, in addition to the negative magnetoresistanee related to spin-dependent interracial tunnelling below To. For (La0.83Sr0.17MnO3)0.6(ITO)0.4, the magnetoresistive ratio for the PMR can reach 39.3% under a magnetic field H=2.24×10^5A/m. Theoretical analysis suggests that the magnetic-field-induced broadening of the p-n barrier between both kinds of grains and the density of the p-n heterostructures should be responsible for the PMR behaviour. 相似文献
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The investigation of the manganites La2/3−xPrxSr1/3MnO3, La2/3Sr1/3−xCaxMnO3 and La2/3+xCa1/3−2xAgxMnO3, which all exhibit Mn3+:Mn4+=2, shows that it is possible to reach high magnetoresistance at room temperature, up to 21% under 1.2 T. These materials are compared to La5/6Ag1/6MnO3 which corresponds to the same Mn3+:Mn4+ ratio and exhibits a magnetoresistance of 25% in this field. An interesting feature deals with the value of the insulator-metal transition temperature TIM, often higher than TC, especially for Ag-based compounds. It is suggested that the latter results either from a better oxygenation of the surface of the grains or from a migration of silver toward the surface. 相似文献
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We report the growth of single phase, c-axis aligned thin films of La1.2Ca1.8Mn2O7 on SrTiO3 (001) substrates using a controlled pulsed laser deposition method. In this method, constraint of epitaxy is utilized to stabilize the Ruddlesdon-Popper (RP) phase of La1.2Ca1.8Mn2O7. Oxygen ambient pressure and the rate of deposition play a very important role in influencing the epitaxial growth as well as maintaining phase purity of the material. The oxygen pressure inside the deposition chamber was very precisely controlled and varied during the layer-by-layer growth of the film. Films, prepared by our method, show excellent electrical and magnetic characteristics with a sharp metal-insulator transition at TM-I=90 K, closely followed by a magnetic transition at TC=91 K. 相似文献