共查询到19条相似文献,搜索用时 171 毫秒
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研究了(Fe1-xWx)84.5B15.5(x=0—0.1)非晶态合金的电阻率ρ与温度T(4.2—300K)的关系。实验结果表明,在所研究浓度区域内均出现电阻率与温度关系的极小值,电阻率极小值的温度Tmin在x=0.06时出现峰值。用x=0.02—0.1浓度区域内,当Tmin时,又出现了电阻率与温度关系的极大值,电阻率极大值的温度Tmax在26—35K之间。低温电阻率反常现象与类Kondo效应及局域磁矩之间RKKY相互作用有关。
关键词: 相似文献
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非晶态(Fe_(1-x)Mn_x)_(84)B_(16)(x=0,0.01,0.02,0.04,0.06)合金采用单辊急冷法制备,用四端引线法测量了4.2—300K温区样品的电阻率与温度的关系.所有样品的电阻率与温度关系中都呈现出极小值.在极小值温度T_(min)以下,电阻率与-lnT成线性变化,在T>T_(min)时,电阻率与T~2成线性变化.室温温度系数α(RT)=1/ρRT dρ/dT和低温区β=1/ρdρ/d(T~2)的数值随Mn含量x的增加而明显下降,这一现象用推广的Ziman理论和局域自旋涨落效应作了讨论. 相似文献
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用固相反应法制备了La0.67Sr0.08Na0.25MnO3样品.通过磁化强度-温度(M-T)曲线、电阻率-温度(ρ-T)曲线以及ρ-T拟合曲线研究了样品的输运性质及庞磁电阻(colossal magnetoresistance,CMR)效应.结果表明,ρ-T曲线和磁电阻-温度(MR-T)曲线均出现双峰现象;高温峰是伴随顺磁-铁磁(PM-FM)相变出现绝缘体-金属(I-M)相变,低温峰是颗粒界面效应;两个绝缘相输运机理不同:较低温度下(248K<T<274K),ρ(T)符合极化子的可变程跃迁模型,而在更高温区(330K<T<374K),ρ(T)符合极化子近邻跃迁模型;两个类金属相输运机理也不同:在低温区(67K<T<186K),满足ρ-T2.5关系,输运机理是自旋波散射和电-磁子散射作用,而在高温区(292K<T<304K),满足ρ-T2关系,输运机理是单磁子散射作用.
关键词:
庞磁电阻
金属-绝缘体转变
晶界效应
输运行为 相似文献
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利用溶胶-凝胶法制备了纳米多晶La0.7Sr0.3MnO3-δ(LSM)块体样品.详细研究了在不同烧结温度下的LSM样品电阻率随测量温度的变化关系和磁电阻效应.随着测量温度从室温降低,电阻率ρ都在250K附近存在最大值,低于该温度后,样品表现为金属导电特性,随后在50K左右存在一极小值.即随着温度从50K左右降低到4.2K,ρ反而逐渐升高,表现为绝缘体性的导电特性.研究表明,在低温下(<50K),ρ随温度降低而升高的现象与隧穿效应的理论模型(lnρ∝T1/2)符合得很好,表明这种现象是由于传导电子在通过邻近LSM晶粒间表面/界面层时的隧道效应所致.而在50—250K的温度范围内,其电阻率与T2成正比,表现为LSM本征的金属导电特性.因此这种低温下电阻率的极小值现象来源于隧穿效应和LSM晶粒本征的金属导电特性的相互竞争.本文还详细研究了相应的隧道磁电阻效应.
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0.7Sr0.3MnO3-δ')" href="#">多晶La0.7Sr0.3MnO3-δ
隧道效应
隧道磁电阻效应 相似文献
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P. Guzdek J. Pszczo?aJ. Chmist P. Stoch 《Journal of magnetism and magnetic materials》2011,323(5):427-431
Synthesis by arc melting, the structural and the electric properties of Y(Co1−xNix)2 alloys were studied by X-ray diffraction (XRD) and four probe dc electrical measurements. XRD analysis (300 K) shows that all samples crystallize in a cubic MgCu2-type structure. The lattice parameters linearly decrease with Ni content. Electrical resistivity for the Y(Co1−xNix)2 intermetallic series was measured in a temperature range of 15-1100 K. The parameters involved in the dependence of resistivity on temperature were determined. Residual, phonon and spin fluctuations resistivity were separated from electrical resistivity using both the Matthiesen formula and the Bloch-Gruneisen formula. The spin fluctuations resistivity of the Y(Co1−xNix)2 series are compared to the mean square amplitudes of spin fluctuations previously calculated by the Linear Muffin Tin Orbital-Tight Binding Approach method for these series in the literature. The contribution of spin fluctuations to total resistivity ρsf is proportional to T2 at low temperatures. The proportionality parameter strongly reduces across the Y(Co1−xNix)2 series. 相似文献
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Igor Dubenko Mahmud Khan Arjun Kumar Pathak Bhoj Raj Gautam Shane Stadler Naushad Ali 《Journal of magnetism and magnetic materials》2009,321(7):754-757
The Mn-based Heusler alloys encompass a rich collection of useful materials from highly spin-polarized systems to shape memory alloys to magnetocaloric materials. In this work we have summarized our studies of magnetostructural transitions from paramagnetic austenite to ferromagnetic martesite phases at TMC in Ni2MnGa-based alloys (Ni2Mn0.75Cu0.25-xCoxGa, Ni2Mn0.70Cu0.30Ga0.95Ge0.05, Ni2Mn1-xCuxGa, Ni2+xMn1-xGa, and Ni2Mn0.75-xCuxGa), and martensitic transitions from the ferromagnetic austenite to the martesite state in off-stoichiometric Ni-Mn-(In/Sb) Heusler alloys. The phase transition temperatures and respective magnetic entropy changes (ΔS) depend on composition in these systems and have been determined from magnetization measurements in the temperature interval 5-400 K, and in magnetic fields up to 5 T. It is shown that, depending on the composition and doping scheme the “giant” ΔS=40-60 J/(kgK) (for a field change of 5 T) can be observed in the temperature range (300-360 K) for the Ga-based alloys. The interplay between or coupling of the various transitions in Ni2Mn(Mn,X) systems with X=Sb and In leads to exchange bias effects, giant magnetoresistance, and both inverse and “normal” magnetocaloric effects. 相似文献
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The resistivities of six FexNi80-xP14B6 alloys have been measured between 1.5 and 50 K. It is found that the resistivity variations both below and above the resistivity minima depend on the transition metal composition. The room temperature coefficients of the resistivity indicate the existence of the magnetic contribution to the resistivity. 相似文献
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本文报道,通过对Y1-xCaxBa2Cu3-xMxO7-δ(M=Fe,Ni)体系样品的晶体结构、氧含量、正常态电阻率与温度的关系,以及超导转变温度等测量,并与YBa2Cu3-xMxO7-δ(M=Fe,Ni)体系进行比较,发现Y1-xCaxBa2Cu3-xFexO7-δ体系的Tc显著地高于相应x值的YBa2Cu3-xFexO7-δ体系,而Y1-xCaxBa2Cu3-xNixO7-δ体系则相反,Tc低于仅Ni替代的体系,表明Ca和Fe同时替代时两者引起的载流子浓度(nH)变化相互补偿,抑制了仅Fe替代时引起的nH和Tc急剧下降;而作Ca和Ni同时替代时主要的不是两者引起载流子浓度变化的相互补偿,Ca和Ni替代效应之间的关联较弱。作者认为,对Y1-xCaxBa2Cu3-xFexO7-δ体系属于CuO2平面外的元素替代,这时载流子浓度是决定Tc的主要因素;而对Y1-xCaxBa2Cu3-xNixO7-δ体系,由于Ni2+离子主要占据Cu(Ⅱ)位,它导致磁拆对效应,Ni2+离子的拆对效应是引起Tc下降的直接原因。
关键词: 相似文献
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In the dilute alloys (La1-xNdx)Sn3 a large anomalous contribution to the zero field Hall constant has been found, which is proportional to the magnetic susceptibility of the Nd3+ ions. On the other hand no corresponding effect appears in (La1-xGdx)Sn3. We conclude that the observed anomalous Hall effect is due to the orbital exchange scattering of the conduction electrons by the Nd-impurities. The coupling energy of this interaction is found to be of the same order of magnitude or even larger than that of the isotropic spin exchange interaction 相似文献
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M. Gaudry J. Lermé E. Cottancin M. Pellarin B. Prével M. Treilleux P. Mélinon J.-L. Rousset M. Broyer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):201-204
Optical properties of mixed clusters (AuxAg
1 - x
)
n
and (NixAg
1 - x
)
n
, produced by laser vaporization and embedded in an alumina matrix, are reported. The size effects are investigated for different
concentrations (x
= 0.25, 0.5 and 0.75) in the diameter range 2-4 nm. For alloyed clusters (AuxAg
1 - x
)
n
of a given size an almost linear evolution of the surface plasmon frequency ω
s
with the concentration is observed (between those of pure gold and pure silver clusters). Moreover the blue-shift and the
damping of the resonance with decreasing size is all the more important as the gold concentration in the particles increases.
Such results are in agreement with theoretical calculations carried out in the frame of the time-dependent local-density-approximation
(TDLDA) including an inner skin of ineffective screening and the porosity of the matrix. The optical response of (NixAg
1 - x
)
n
clusters exhibits a surface plasmon resonance in the same spectral range as the one observed for pure silver clusters, but
considerably damped and broadened. For a given mean cluster size 3.0 nm, a blue-shift of the resonance is observed when increasing
the nickel concentration (between x
= 0.25 and x
= 0.75). The results are in good qualitative agreement with classical predictions in the dipolar approximation, assuming a core-shell
geometry.
Received 21 November 2000 相似文献
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在0.0001-2.4GPa流体静压力范围详细研究了非晶(Fe1-xCox)77.5Nd4B18.5(0≤x≤1.0)合金的电阻率与压力的关系,得到该非晶合金电阻率的压力系数随组分x变化的规律。结果表明:用少量的钴(x=0.2)替代铁,不会影响其硬磁性和热稳定性,同时却可减小电阻率的压力系数,从而增强电磁性能在压力下的稳定性。此外还观测到在0.51GPa保压3-24h的结构弛豫,进一步求出该非晶台金电阻率的压力弛豫时间对组分x的依赖关系。
关键词: 相似文献