Enhancement of magnetoresistances at room temperature in YSZ doping La0.67Sr0.33MnO3 system

The temperature dependence of the resistance of composite samples (1−x)La_0.67Sr_0.33MnO₃+xYSZ with different YSZ doping level x was investigated at magnetic fields 0-3 T, where YSZ represents yttria-stabilized zirconia. Results show that the YSZ dopant does not only adjust the metal-insulator transition temperature, but also increases the magnetoresistance effect. With increase of YSZ doping level for the range of x<2%, the metal-insulator transition temperature values T_P of the composites decrease, but T_P increases with increase of x further for the range of x>2%. Meanwhile, in the YSZ-doped composites, a broad metal-insulator transition temperature region was found at zero and low magnetic field, which results in an obvious enhanced magnetoresistance in the temperature range 10-350 K. Specially, a larger magnetoresistance value was observed at room temperature at 3 T, which is encouraging with regard to the potential application of magnetoresistance materials.     

Shubnikov-de haas effect in n-CdSnAs2

Shubnikov-de Haas oscillations in the transverse magnetoresistance of single-crystalline n-type CdSnAs₂ have been recorded at temperatures between 2 and 25 K in magnetic fields up to 5T. The electron concentration of the samples ranged from 2 × 10¹⁷ to 2 × 10¹⁸ cm^?3. The angular dependences of the oscillation periods and cyclotron effective masses showed that the conduction band exhibits an energy dependent anisotropy, obeying the Kildal band structure model. For the low-temperature values of the band parameters we found: a band gap E_g = 0.30 eV, a spin-orbit splitting Δ = 0.50 eV, a crystal field splitting parameter δ = ?0.09 eV, and an interband matrix element P = 8.5 × 10^?8eV cm. This simple four-level model was found to be not adequate to describe quantitatively the observed electronic effective g-factor for a sample with low electron concentration.     

High-field magnetoresistance of polycrystalline ZrZn2

We report magnetoresistance measurements of polycrystalline ZrZn₂ as a function of temperature (4.2–48K) and magnetic field up to 19 T. The results indicate the presence of both positive and negative contributions to the magnetoresistance. The latter is due to spin fluctuations. Below T_c the resistivity varies with temperature like T² over the entire field range (0–19 T). The coefficient of the T² -term decreases with increasing field and fits a $\text{H}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>3</mtext>}}$ dependence above ～ 10 T, in accordance with theoretical predictions. Complex behaviour of the magnetoresistance is found in the paramagnetic regime above ～ 5 T.     

Low temperature magnetoresistance in La1.32Sr1.68Mn2O7 layered manganite under hydrostatic pressure

The La_1.32Sr_1.68Mn₂O₇ layered manganite system has been studied by the low temperature electrical resistance and magnetoresistance under hydrostatic pressure up to 25 kbar. We have observe both, a Curie temperature (T_C) and a metal-insulator transition (T_MI) at 118 K in the ambient pressure. The applied pressure shifts the T_MI to higher temperature values and induces a second metal-insulator transition (T²_MI) at 90 K, in the temperature dependence of resistivity measurements. Also, the pressure suppresses the peak resistance abruptly at T_C. When an external field of 5 T is applied, we have observed a large negative magnetoresistance of 300% at the transition temperature and a 128% at 4.5 K. However, the increased pressure decreases the magnetoresistance ratio gradually. When the pressure reaches its maximum available value of 25 kbar, the magnetoresistance ratio decreases at a rate of 1.3%/kbar. From our experimental results, the decrease of magnetoresistance ratio with pressure is explained by the pressure induced canted spin state which is not favor for the spin polarized intergrain tunneling in layered manganites.     

Transport properties of n-type ferromagnetic semiconductor HgCr2−xInxSe4(x = 0.100)

Measurements of the electrical conductivity, magnetoresistance, and Hall effect were performed on a n-type ferromagnetic semiconductor HgCr_2?xIn_xSe₄(x = 0.100) single crystal from 6.3 to 296 K in magnetic fields up to 1.19×l0⁶A/m. The conductivity decreases rapidly near the Curie temperatureT_c (≈120 K) as the temperature is raised. A large peak in the magnetoresistance is observed near T_c. The Hall effect measurements indicate that the temperature dependence of the conductivity and the magnetoresistance are due mostly to a change in electron mobility. The electron mobility is 1.2 × 10^?2 m²/V · s at 6.3 K, and decreases rapidly near T_c with the rise in temperature. Then it increases slowly from 5.5 × 10^?4 m²/V · s at 160 K to 7.5 × 10^?4 m²/V · s at 241 K. This temperature dependence of the electron mobility can be explained in terms of the spin-disorder scattering which takes into account the exchange interaction between charge carriers and localized magnetic moments.     

La1-xCaxMnO3的巨磁电阻效应

通过测量La_2/3Ca_1/3MnO₃，La_0.6Ca_0.4MnO₃单相多晶样品的磁电阻、电阻与温度的依赖关系，发现在La_1-xCa_xMnO₃体系中随x的变化，其磁电阻峰和电阻峰都发生了位移．作者认为体系中Mn⁴⁺含量是受Ca含量调制的，正是Mn⁴⁺含量的变化，导致磁性 关键词：     

巨磁电阻材料La0.9Sr0.1MnO3与半导体Si组成的二极管的整流特性

掺杂锰氧化物La_0.9Sr_0.1MnO₃薄膜被直接沉积在n型 硅基片上，构成p-n结.这种p-n结在很宽的温度范围内都有很好的整流特性.研究结果表明， 这种p-n结的结电阻对低磁场敏感，在3×10^-2T的磁场下，磁电阻可达70％.磁 电阻的正负依赖于温度.磁电阻的大小可通过加在p-n结上的电压调节.     

Pulsed magnetic field study of the spin gap in intermediate valence compound SmB6

In this work, we report the behavior of electrical resistivity of SmB₆ at temperatures between 2.2 and 70 K in pulsed magnetic fields up to 54 T. A strong negative magnetoresistance was detected with increasing magnetic field, when lowering the temperature in the range T<30 K. We show that the amplitude of negative magnetoresistance reaches its maximum dR/R~70% at B=54 T, in the vicinity of phase transition occurring in this strongly correlated electron system at T_C~5 K. The crossover from negative magnetoresistance to positive magnetoresistance found at intermediate temperatures at T>30 K is discussed within the framework of exciton-polaron model of local charge fluctuations in SmB₆ proposed by Kikoin and Mishchenko. It seems that these exciton-polaron in-gap states are influenced both by temperature and magnetic field.     

Room temperature magnetoresistance in Ln2/3A1/3MnO3 manganites

The investigation of the manganites La_2/3−xPr_xSr_1/3MnO₃, La_2/3Sr_1/3−xCa_xMnO₃ and La_2/3+xCa_1/3−2xAg_xMnO₃, 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 La_5/6Ag_1/6MnO₃ 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 T_IM, often higher than T_C, 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.     

钙钛矿（La1-yTby)0.67Sr0.33MnO3的磁致伸缩效应

采用固相反应烧结法制备了（La_1-yTb_y)_0.67Sr_0.33MnO₃系列样品（y=0,0.05,0.15,0.20,0.25,0.33,0.40,0.50,0.60,1.00).X射线衍射表明,随着y值增大钙钛矿型晶体结构从菱面对称性向正交对称性转变.180K时,μ₀H=7T条件下,在y=0.40样品的巨磁电阻可达900％.μ₀H=1.7T时,y=0.20样品的室温磁致伸缩为-50×10^-6.210K时,y=0.33样品的磁致伸缩可达-130×10^-6. 关键词：     

Inelastic magnetic X-ray scattering from highly correlated electron systems: La1.2Sr1.8Mn2O7, La0.7Sr0.3MnO3 and Fe3O4

Magnetic Compton profiles have been measured for the colossal magnetoresistance manganites La_1.2Sr_1.8Mn₂O₇ and La_0.7Sr_0.3MnO₃, and for magnetite Fe₃O₄, along various crystallographic directions, over a wide range of temperatures and magnetic fields. The experimental results are interpreted via first-principles computations for the double layer manganite, La_1.2Sr_1.8Mn₂O₇, and by using a simple model involving atomic d-orbitals and free electrons for the other two compounds. For all three materials a preference for the occupation of e_g orbitals is found, particularly, for orbitals of dx²−y² symmetry. An itinerant electron contribution is adduced at all temperatures in magnetite; such a contribution also appears in La_1.2Sr_1.8Mn₂O₇, but it is present only at low temperatures in La_0.7Sr_0.3MnO₃.     

Electrical resistance and magnetoresistance of amorphous alloys Gd67Co33 and Pd80Si20

In search for structural contributions to the low temperature anomaly we report high resolution resistance and magnetoresistance measurements ($\text{0.02}\text{K}\text{? T ? 20}\text{K}$) of amorphous splats of Gd₆₇Co₃₃ and Pd₈₀Si₂₀. For both alloys, the resistivity ?(H = 0, T) has a minimum at T ～ 10 K and increases with decreasing T. The ferromagnetic Gd₆₇Co₃₃ shows a strong negative field dependence of $\text{Δ?}\text{?(0)}$, saturating at H ～ 2T for T = 4.2 K but no measurable change in $\text{??}\text{?}\text{T}$ below 10 K is observed.The diamagnetic Pd₈₀Si₂₀ exhibits a positive field dependent magnetoresistance $\text{[Δ?}\text{?(0)]}\text{(}\text{H}\text{)}$ at low temperatures. Additionally, a field dependent part in $\text{??}\text{?}\text{T}$ is found which is probably due to paramagnetic impurities (～ 1 ppm Fe). However, there is also a field independent contribution in the amorphous state of Pd₈₀Si₂₀, which vanishes after crystallization. We attribute this to non-magnetic scattering induced by the disordered structure.     

Magnetoresistance of Sc3In

The magnetoresistance of the weak itinerant-electron ferromagnet Sc₃In was measured from 1.5 to 40 K in magnetic fields up to 14 T. The measurements were made on three samples containing 24.1, 24.3 and 24.4 at% In with Curie temperatures at H = 0 of T_c(0) = 5.5, 6.0 and 6.3 K, respectively. By assuming that the characteristic spin-fluctuation temperature is equal to T_c(0), the negative magnetoresistance in Sc₃In was systematically and reasonably analyzed in terms of the quenching of spin fluctuations by magnetic fields.     

The relation between magnetoresistance and magnetocaloric effect in La0.85Ag0.15MnO3 manganite

We present the temperature dependence of La_0.85Ag_0.15MnO₃ resistivity in the temperature interval between 77 and 340 K and magnetic fields up to 26 kOe. We offer a method of separating tunnel magnetoresistance from total magnetoresistance. A change in both the magnetic entropy, which is caused by the magnetocaloric effect (MCE), and the magnetoresistance are shown to be connected through a simple relationship to La_0.85Ag_0.15MnO₃.     

Observation of large magnetic resistance in weak magnetic fields using CuPt/SiO2/Si/SiO2/CuPt structure

The magnetoresistive effect of CuPt(8 nm)/SiO₂(5 nm)/Si(50,000 nm)/SiO₂(5 nm)/CuPt(8 nm) structure made by e-beam evaporation technique is studied in this work. Variation in magnetoresistance obtained by I-V measurements at 77 K and in the presence of less than 5 mT magnetic field applied in parallel to the surface is investigated. We have found that this structure exhibit large magnetoresistance in low magnetic fields (i.e. <5 mT). Our results also indicate that the variation in magnetoresistance in the presence of external magnetic field has oscillatory behavior and has the maximum value of 3295%. This structure due to its high sensitivity to low magnetic fields can also be used as an active element in magnetic field sensor devices.     

机械合金化La0.7Ca0.3MnO3的晶化动力学及磁电阻研究

通过机械合金化方法制备了单相La_0.7Ca_0.3MnO₃化合物.球磨形成的非晶态结构在920K退火时转变为钙钛矿型相结构.根据质量作用定律,讨论了非晶晶化动力学行为,其晶化转变激活能约为265kJ/mol.同时研究了化合物的电阻特性,发现低温下样品的电阻ρ与温度T的关系为ρ∝T²,随退火温度的升高,ρ-T²曲线斜率下降.在远离居里温度处的低温磁电阻可用Δρ/ρ₀=p₁-p₂T^3/2-p₃T描述. 关键词：     

Galvanomagnetic properties of n-type Hg0.8Cd0.2Te

Galvanomagnetic properties of low and high mobility n-Hg_0.8Cd_0.2Te are reported. The experiments were carried out in magnetic fields up to 60 kG and between 1.8 and 77 K. The Hall coefficient does not show thermal and magnetic freeze-out of carriers. At 77 K the transversal magnetoresistance shows a proportionality ?⊥ ∝ B as was predicted by Gurevich and Firsov for the case of polar optical scattering in non-degenerated semiconductors. At 4 K where the mobility is governed by impurity scattering ?⊥ ∝ B^2.4 was observed in the extreme quantum limit. A negative longitudinal magnetoresistance was found at 77 K. The experimental results of high and low mobility samples show significant differences.     

Magnetic properties of PrRh2Si2: A neutron diffraction study

The magnetic properties of polycrystalline PrRh₂Si₂ sample have been investigated by neutron diffraction measurements. Antiferromagnetic transition with an anomalously high ordering temperature (T_N∼68 K) is clearly observed in magnetic susceptibility, specific heat, electrical resistivity and neutron diffraction measurements. Neutron diffraction study shows that Pr³⁺ ions carry an ordered moment of 2.99(7)μ_B/Pr³⁺ and align along the crystallographic±c-directions for the ions located at the (0,0,0) and positions. The magnetoresistance at 2 K and 10 T is rather large (∼35%).     

Temperature and field dependent electronic structure and magnetic properties of LaCoO3 and GdCoO3

The transformation of the band structure of LaCoO₃ in the applied magnetic field has been theoretically studied. If the field is below its critical value B_C≈65 T, the dielectric band gap decreases with the field, thus giving rise to negative magnetoresistance that is highest at T≈300÷500 K. The critical field is related to the crossover between the low- and high-spin terms of Co³⁺ ions. The spin crossover results in an insulator–metal transition induced by an increase in the magnetic field. Similar calculations have been done for GdCoO₃ which is characterized by large spin gap∼2000 K.     

Magnetic and electric properties of the colossal magnetoresistance manganite Sm1.4Sr1.2Ca0.4Mn2O7

Polycrystalline Sm_1.4Sr_1.2Ca_0.4Mn₂O₇ has been successfully synthesized and investigated with respect to its magnetic and electrical properties. It is found that the sample shows a metal insulator (M-I) transition at 88 K. The maxima of the magnetoresistance (MR) ratio are 95.38% and 98.55% under applied fields of 2 T and 5 T, respectively. At 10 K, the MR attains ∼75% at 5 T. The large MR at low temperature can be attributed to the effects of nearly fully spin-polarized carriers tunneling through the insulating (Sm, Sr, Ca)₂O₂ layers between the adjacent MnO₂ bi-layers. The magnetization data indicates the existence of ferromagnetic clusters.