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La0.67Ca0.33MnO3 and La0.67Ca0.33Mn0.96Fe0.04O3单晶的磁性和磁电阻特性。由于缺少晶粒间界,磁场对于自旋涨落的抑制作用更加明显,所以单晶中的磁电阻率比多晶的提高了两个数量级。通过Fe的掺杂,在40×105A/m的磁场下,磁电阻率从3400%进一步提高到了17600%。通过对居里温度以上电阻率的小极化子模型拟和的结果,我们看到随着Fe的掺杂,激活能被提高。磁极化子激活能的增大可以更加局域电子,这可能是在Fe掺杂单晶中本征磁电阻率进一步提高的主要原因。 相似文献
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系统研究了室温下Tb0.3Dy0.7(Fe1-xAlx)1.95(x=0,0.05,0.1,0.15,0.2,0.25,0.3,0.35)合金中金属Al替代Fe对晶体结构、磁致伸缩、各向异性和自旋重取向的影响.结果发现,x<0.4时,Tb0.3Dy0.7(Fe1-xAlx)1.95完全保持MgCl2立方Laves相结构,晶格常量a随Al含量x的增加而增大.磁致伸缩测量发现,随着替代量x的增多磁致伸缩减小,x>0.15时超磁致伸缩效应消失 x<0.15时磁致伸缩在低场下(H≤4kAm)有小幅增加,高场下迅速减小,而且易趋于饱和,说明添加少量Al有助于减小磁晶各向异性.内禀磁致伸缩λ111随Al替代量x的增加大幅度降低.对于0≤x<0.15,穆斯堡尔效应表明,随Al含量的增加Tb0.3Dy0.7(Fe1-xAlx)1.95合金中发生了自旋重取向,易磁化方向经历了[111]→[uv0]→[uvw]的转变.由相对磁化率随温度的变化关系可以看出,Al替代Fe使自旋重取向温度降低.当x=0.15时,Tb0.3Dy0.7(Fe1-xAlx)1.95合金中出现了少量非磁性相 x>0.15时,合金在室温下呈现顺磁性
关键词:
磁致伸缩 立方Laves相 自旋重取向 各向异性 穆斯堡尔谱 相似文献
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系统研究了室温下Tb0.3Dy0.7(Fe0.9T0.1)1.95(过渡金属元素T=Mn,Fe,Co,B,Al,Ga)合金中ⅢA族金属和过渡金属元素T替代Fe对结构、自旋重取向和穆斯堡尔谱的影响.结果发现,不同金属T替代Fe,Tb0.3Dy0.7(Fe0.9T0.1)1.95,合金具有相同的MgCu2型立方Laves相结构;Al,Ga替代使Tb0.3Dy0.7(Fe0.9T0.1)1.95合金的易磁化方向在{110}面逐渐偏离了立方晶体的主对称轴,即自旋重取向,B,Mn,Co替代未使易磁化轴发生明显转动;Al,Ga元素替代使超精细场Hhf略有下降,B,Mn替代对超精细场Hhf的影响不大,而Co元素替代使超精细场Hhf有较大增加;所有元素替代使同质异能移IS有所增加;B,Al,Ga和Mn替代使四极劈裂Qs增加,而Co替代使四极劈裂Qs下降.
关键词:
立方Laves相
自旋重取向
穆斯堡尔谱 相似文献
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通过室温下的中子衍射和磁性测量对多晶样品Nd0.5Sr0.4Pb0 .1MnO3 的结构和磁性进行了实验研究.中子衍射结果表明,该样品具有正交的钙钛矿结构,空间群 是Pnma,即结构发生了晶场畸变.由M-T和R-T曲线可知,居里温度TC=273 K ,其特征是随着温度的增加样品经历了从铁磁金属态转变到顺磁半导态,且转变温度T p=225 K;用锰氧化物晶场和双交换作用的竞争解
关键词:
结构
磁性
中子衍射
晶场畸变
p')" href="#">转变温度Tp
双交换作用 相似文献
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系统研究了室温下Tb0.3Dy0.7-xPrx(Fe0.9Al0.1)1.95 (x=0,0.1,0.2,0.25,0.3,0.35)合金中稀土元素Pr替代Dy对晶体结构、磁致伸缩、各向异性和自旋重取向的影响. 结果发现,x≤0.1时,Tb0.3Dy0.7-xPrx(Fe0.9Al0.1)1.95完全保持MgCl2立方Laves相结构,0.1<x≤0.3,有杂相出现并且随Pr替代量逐渐增多;晶格常数a随Pr含量x的增加缓慢增大. 磁致伸缩测量发现,随着替代量x的增多磁致伸缩减小;x>0.2时超磁致伸缩效应消失. 然而,x=0.1时合金的磁致伸缩略大于没有替代的,而且磁致伸缩随磁场更易趋于饱和,说明Pr替代有助于降低磁晶各向异性. 内禀磁致伸缩λ111随Pr替代量x的增加接近线性增加. 由相对磁化率随温度的变化关系可以看出,自旋重取向温度随Pr替代量的增多呈先增后降趋势,在x=0.1处出现极大值. 穆斯堡尔效应表明,随Pr含量的增加Tb0.3Dy0.7-xPrx(Fe0.9Al0.1)1.95合金中易磁化轴可能在{110}面上绕主对称轴作微小转动,发生自旋重取向. 与Al元素替代效应相比,Pr替代Dy对自旋重取向的影响相对较小. 相似文献
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利用固相反应法制备Pr0.5Ca0.5MnO3(PCMO)靶材,并采用脉冲激光沉积法(PLD)在n型Si(111)基片上沉积PCMO外延薄膜,研究了薄膜的输运特性及薄膜与Si衬底形成异质结的整流特性.结果表明:在80—300 K温度范围内,PCMO薄膜的阻温关系符合变程跳跃模型,随着温度的升高表现出从一维到二维再到三维的转变,分析认为可能源于轨道自由度对电子输运特性的影响.PCMO/Si异质结在磁场作用下整流特性得到改善,且在正向电流方向出
关键词:
0.5Ca0.5MnO3')" href="#">Pr0.5Ca0.5MnO3
Si
整流
正磁电阻 相似文献
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The structure and magnetic properties of Nd_{0.5}Pb_{0.5-x}Sr_xMnO_3 (0≤x≤0.4) manganites were systematically investigated. Significant changes in Curie temperature and metal-insulator (MI) transition temperature of the samples were observed. All samples exhibited a transition from paramagnetic semiconducting to ferromagnetic metallic state. Curie temperature T_C and the MI transition temperature T_p increased with increasing Sr content. We attributed these behaviours to the enhancing of both the double exchange mechanism and the Jahn-Teller electron-phonon coupling. 相似文献
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研究了Nd0.5Ca0.5MnO3体系的结构和输运特性. 结构 分析表明,在300K下,体系表现为O′型正交结构并存在典型的Jahn-Teller畸变.在8 T磁场 下,体系出现顺磁绝缘-铁磁金属的转变,庞磁电阻效应发生. 磁测量发现,样品的奈尔温 度TN和电荷有序转变温度TCO分别在150和240K左右,在41K左右出 现典型再入型自旋玻璃行为,同时观察到了负的磁化率异常. 结果表明,Nd关键词:
庞磁电阻
自旋玻璃态
负磁化强度
电荷有序 相似文献
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We report here on the characterisation by temperature programmed reduction, 57Fe Mössbauer spectroscopy and X-ray absorption spectroscopy of the phases resulting from treatment of the perovskite-related material La0.5Sr0.5Fe0.5Co0.5O3 in a flowing 90% hydrogen/10% nitrogen atmosphere. The results show that treatment of La0.5Sr0.5Fe0.5Co0.5O3 (which contains approximately 50% Fe4+ and 50% Fe3+) in the flowing 90% hydrogen/10% nitrogen atmosphere at 600°C does not result in the reduction of any of the constituent elements of the material and that the perovskite structure is still retained. The Mössbauer spectrum recorded following heating in the gaseous reducing environment at 1,000°C shows the presence of metallic iron, an Fe3+-containing phase with parameters compatible with the presence of SrLaFeO4 which has a K2NiF4-type structure, and a paramagnetic Fe3+ phase. The X-ray absorption spectroscopy results show the presence of metallic cobalt. The Mössbauer spectrum recorded following heating at 1,200°C continues to show the Fe3+-containing components plus a larger contribution from metallic iron. The X-ray absorption spectroscopy results show the presence of metallic cobalt, SrLaFeO4, La2O3 and SrO. 相似文献
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Effect of preparation procedure on the magnetic and transport properties of double perovskite Sr2FeMoO6
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Ordered and disordered double perovskite Sr2FeMoO6 ceramics have been investigated by powder x-ray diffraction,magnetic and transport measurements, as well as Moessbauer spectroscopy. The heavily disordered sample can be acquired by annealing the ordered samples in argon. The annealing procedure affects not only the nature of grain boundaries but also the grain itself. The evidence of Moessbauer spectra performed at 77 and 300K indicates that there exist small oxygen deficient clusters of SrFeO3-y in the disordered sample. The paramagnetic Fe^4 and Fe^3 ions in the compound subsist down to 77K and the ratio of Fe^4 /Fe^3 increases with decreasing temperature. 相似文献
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Tin-doped compounds of spinel-related M3O4 (M = Fe, Mn, Co) have been studied by 119Sn and 57Fe Mössbauer spectroscopy in the temperature range of 20–600 K. The 119Sn Mössbauer spectra recorded down to 20 K from the non-iron-containing compounds of Co3O4 and Mn3O4 contained only doublets showing no transfer of magnetic properties from cobalt or manganese to the dopant tin ions. In contrast, the tin-doped-(FeCo)3O4 and (FeMn)3O4 gave 119Sn and 57Fe Mössbauer spectra, which showed magnetic hyperfine interactions. The Curie temperature has been estimated for the former sample. 相似文献
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W. Barona Mercado M. Fajardo G. A. Pérez Alcázar H. Sánchez Sthepa 《Hyperfine Interactions》2006,168(1-3):943-949
Double iron and aluminum carbides were prepared by mechanical alloying from elemental powders, with a ball-to-powder weight ratio 20:1. The samples were milled for 1, 3, 5, 10, 15, 20 and 25 h. The alloy progress for each milling time was evaluated by X-ray diffraction (XRD) and 57Fe Mössbauer spectroscopy. Once the alloy was consolidated two sorts of paramagnetic sites and a magnetic distribution were detected according to the Mössbauer fit. The majority doublet could correspond to Fe3AlC0.5 carbide as X-ray diffraction suggest, and the other could be Fe3AlC0.69; the magnetic distribution corresponding to Fe3Al phase, Fe7C3 and Fe5C2 single carbides. The hyperfine parameters are reported. 相似文献
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The effect of IIIA metal and transition metalT substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation
of a series of polycrystalline Tb0.3 Dy0.7 (Fe0.9
T
0.1)1.95 (T=Mn, Fe, Co, B, Al, Ga) alloys at room temperature were investigated systematically. It was found that the primary phase of
the Tb0.3 Dy0.7 (Fe0.9
T
0.1)1.95 alloys is the MgCu2-type cubic Laves phase structure for different substitution. The magnetostriction λ{ins} decrases greatly for the substitution
of IIIA metal, B, Al and Ga, but is saturated more easily for Al and Ga substitution, showing that the Al and Ga substitution
is beneficial to a decrease in the magnetocrystalline anisotropy of Tb0.3 Dy0.7 (Fe0.9
T
0.1)1.95 alloys. However, the substitution of transition metal Mn and Co decreases slightly the magnetostriction λ{ins}. It was also
found that the effect of different substitutions on the spontaneous magnetostriction λ{in111} is distinct. The analysis of
the M?ssbauer spectra indicates that the easy magnetization direction in the {110} plane deviates slightly from the main axis
of symmetry for Al and Ga substitution, namely spin reorientation, but it does not change evidently for B, Mn and Co substitution. 相似文献
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