Conductivity, magnetoresistance, and the Hall effect in granular Fe/SiO2 films

We have investigated the conductance, magnetoresistance, and Hall effect in granular Fe/SiO₂ films with size of the iron grains around 40 Å, whose volume fraction x lies in the range 0.3–0.7. The conduction activation regime has been established for x<0.6. On the insulator side of the transition we observed a giant negative magnetoresistance, falling off sharply as the metal volume fraction decreases. For x<0.4 we observed a large positive magnetoresistance of premagnetized samples, showing up in fields; ～100 Oe and characterized by large response times. The field dependence of the Hall effect in the dielectric samples, as in the metallic samples, correlates with their magnetization. We found that the Hall resistance is proportional to the square root of the longitudinal resistance, which cannot be explained by known models of the anomalous Hall effect.     

New type of conductivity?

Experiments yielded rapid rise in the Hall gr_xy and magnetoresistance ρ_xx, ρ_zz in Hg_0.76Cd_0.24Te to almost linear dependence in strong magnetic fields. This paper relates it to the states, which are extended at the Hall edge for ρ_xy and between the Hall edges for ρ_xx, ρ_zz, while bulk states are localized. Theory agrees with experiments, and suggests that thin enough samples may have zero magnetoresistance in strong enough magnetic fields.     

High-field magnetoresistance and Hall effect in Bi2Sr2CuO x single crystals

We investigated the in-plane magnetoresistance and the Hall effect of high-quality Bi₂Sr₂CuO_x single crystals with T _c (midpoint) = 3.7–9.6 K in dc magnetic fields up to 23 T. For T < 10 K, the crystals show the classical positive magnetoresistance. Starting at T ≈ 14 K, an anomalous negative magnetoresistance appears at low magnetic fields; for T ≥ 40 K, the magnetoresistance is negative in the whole studied range of magnetic fields. Temperature and magnetic field dependences of the negative-magnetoresistance single crystals are qualitatively consistent with the electron interaction theory developed for simple semiconductors and disordered metals. As is observed in other cuprate superconductors, the Hall resistivity is negative in the mixed state and changes its sign with increasing field. The linear T-dependence of cotθ_H for the Hall angle in the normal state closely resembles that of the normal-state resistivity as expected for a Fermi liquid picture.     

Mössbauer effect of iron-57 intercalated in layered compound 2H−Fe0.5TaSe2

⁵⁷Fe Mössbauer effect study has been performed on intercalated compound 2H?Fe_0.5TaSe₂ over a temperature range between 14K and 500K. The highly concentrated intercalation samples 2H?Fe_xTaSe₂ with Fe atoms (x up to 2) are prepared by the electrochemical method for the first time. The Mössbauer measurement shows that iron is in Fe³⁺ high spin state and with the same probability occupies both octahedral and tetrahedral interstices of the Van der Waals gap. The fact that effective masses of iron ions in both sites are close to 57 amu and characteristic temperatures (Θ_M =130K, 107K respectively) are found to be relatively small is attributed to the weak forces on Fe³⁺.     

Planar Hall effect and magnetoresistance in Ni81Fe19 and Co square shaped thin films

Ni₈₁Fe₁₉ and Co thin films have been fabricated and their transport properties have been investigated for potential applications in ultra sensitive magnetic field sensors. The Ni₈₁Fe₁₉ films exhibit an anisotropic magnetoresistance (AMR) of 2.5% with a coercivity 2.5 Oe and the Co films exhibit an AMR of 0.7% with coercivity 11 Oe. Large planar Hall effect magnetoresistance values at room temperature are reported for both cases. An unbalanced Wheatstone bridge model is proposed to describe quantitatively the observed experimental Planar Hall Effect data.     

Low-temperature spin relaxation in compacted powders of CrO<Subscript>2</Subscript> solid solutions with iron impurities

The effect iron impurities have on the low-temperature behavior of the magnetoresistance of compacted powders of CrO₂ ferromagnetic half-metal with anisotropic particle shape is investigated. The strong dependence of magnetoresistance on the spin relaxation rate during specimen magnetization reversal is revealed. It is shown that the addition of Fe impurities increases the powders’ coercive force and reduces tunnel magnetoresistance. A resonance mechanism of carrier tunneling in powders of CrO₂ solid solutions with iron impurities is proposed.     

Some peculiarities of magnetoresistance and Hall resistance of Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript> nanoplates

Antimony telluride (Sb₂Te₃) nanoplates of various thickness were grown by the vapor phase deposition method. The Hall resistance and magnetoresistance of the samples were measured in magnetic fields up to 9 T at temperatures from 2 to 300 K. Temperature dependence of the magnetoresistance and Hall resistance of the nanoplates shows a strong dependence on the thickness of the samples. Relatively thick samples show a nonlinear dependence of the Hall resistance on magnetic field. The measurement data are analyzed within the model of multi-channel transport. The difference in behavior is attributed to the existence of two channels of charge transfer with high and low mobility.     

Hall effect and magnetoresistivity in the ternary molybdenum sulfides

We have measured the Hall coefficient and magnetoresistance of sputtered films of Cu_XMo₆S₈ and PbMo₆S₈, as well as the magnetoresistance in sintered samples of the same materials. Assuming a single band model, net carrier densities and mean mobilities are determined.     

非晶态软磁薄膜Fe90-xCoxZr10的平面霍耳效应和磁阻效应

本文研究了非易态软磁薄膜Fe_90-xCo_xZr₁₀的平面霍耳电压及磁阻随磁场方向、成分和温度的变化规律。采用通常的六探针法进行了测量。结果表明平面霍耳电压和磁阻分别满足经验公式V_y=pM²Isin2θ和△ρ=cM²cos2θ;并给出了V_y表达式中的常数项p正比于ρ²。此外,样品Co₉₀Zr₁₀和样品Fe₇₀Co₂₀Zr₁₀晶化前后的V_y变化正好相反,即富钴成分的样品晶化后,V_y增加,而富铁成分的样品V_y下降。 关键词：     

Transport parameters of n-type GaSb

The conduction band parameters of GaSb have been investigated in the temperature region 70–280 K. Hall and magnetoresistance data have been analysed according to the two band model to obtain information about the energy separation ΔE₁₂ of the conduction band minima and its temperature coefficient α₂.     

Low temperature phase transition in the chain-like compounds NbSe3 and TaSe3

New transitions have been observed at low temperature by electrical measurements on the linear trichalcogenides NbSe₃ and TaSe₃. The resistivity of TaSe₃ drops near zero below 1.5 K which may indicate a superconducting transition. The resistivity of NbSe₃ drops below 2.2 K by 30 to 75% of its residual value at 4.2 K. However for TaSe₃ and NbSe₃ initial susceptibility measurements do not show any increase in diamagnetism indicating a flux expulsion. In addition the transitions below the critical temperatures are strongly non-linear with current density higher than 10^-3 A mm^-2.     

Hall effect and negative magnetoresistance in thin crystals of NbSe<Subscript>3</Subscript>

We have measured the Hall effect and the transverse magnetoresistance in NbSe₃ single crystals. In the liquid helium temperature range we observed an absolute negative magnetoresistance (NMR) — the value of the resistance under magnetic field being much lower than that at zero field — in NbSe₃ single crystals with a thickness less than 5 μm with the magnetic field oriented in the (b, c) plane. We show that this NMR effect is observed in the magnetic field range in which the Hall constant changes its sign. The results are qualitatively explained by the change of the surface scattering contribution to the magnetoconductance in the magnetic field range near the Hall voltage zero crossing.     

Reflectivity studies of Ti- and Ta-dichalcogenides: Phonons

The i.r.-spectra of the 1T phases of TiS₂, TiSe₂, TaS₂ and TaSe₂ reveal features attributed to large free carrier densities and to i.r.-active longwavelength phonons. We find a single phonon in TiS₂, TiSe₂ and TaS₂, but six phonons in TaSe₂, The oscillator strengths are significantly higher in the Ti-compounds yielding large values of the infrared effective charge, ～6e, and electron-phonon coupling constant, 0.4–1.0. The observation of many modes in TaSe₂ is attributed to a superlattice distortion driven by a charge density wave.     

Fe15.16Ag84.84金属颗粒膜自旋极化相关的霍尔效应研究

采用磁控溅射法分别在玻璃和单晶硅衬底上同时制备了Fe_15.16Ag_{84.84金属颗粒膜样品，并对样品的霍尔效应和霍尔系数RH随外加磁场H的变化关系进行了 实验研究. 观察到霍尔电压UH与外加磁场H的关系曲线呈现出自旋极化相关的反常现象，并 与其磁电阻效应具有对应关系.基于自旋相关的散射理论对此作出了合理的解释. 关键词： 颗粒膜 霍尔效应 c}')" href="#">特征磁场H_c 自旋相关散射     

Hall,electrical resistivity and magnetoresistivity measurements in MoSi3N4 and TiSi3N4 multilayered thin films

Multilayered thin films of a metal layer (Mo,Ti) alternating with an insulator layer (Si₃N₄) were prepared in an RF diode sputtering sustem. The modulation wavelength Λ was kept constant at 100 Å, although the metal/insulator ratio was varied between .49 to .9. The dc resistivity, magnetoresistance and Hall coefficient were measured from 1.6 to 300K and for magnetic fields up to 2 T. A logarithmic increase of the resistance at low temperatures, a positive magnetoresistance, increased logarithmically for large magnetic fields, and a temperature dependent Hall coefficient indicate that electron interaction effects are the dominant mechanism for a positive TCR below T_min.     

The transport properties of Dirac fermions in chemical vapour-deposited single-layer graphene

Abstract

The electronic transport properties of Dirac fermions in chemical vapour-deposited single-layer epitaxial graphene on anSiO₂/Si substrate have been investigated using the Shubnikov–de Haas (SdH) oscillations technique. The magnetoresistance measurements were performed in the temperature range between 1.8 and 43 K and at magnetic fields up to 11 T. The 2D carrier density and the Fermi energy have been determined from the period of the SdH oscillations. In addition, the in-plane effective mass as well as the quantum lifetime of 2D carriers have been calculated from the temperature and magnetic field dependences of the SdH oscillation amplitude. The sheet carrier density (1.42 × 10¹³ cm^?2 at 1.8 K), obtained from the low-field Hall Effect measurements, is larger than that of 2D carrier density (8.13 × 10¹² cm^?2). On the other hand, the magnetoresistance includes strong magnetic field dependent positive, non-oscillatory background magnetoresistance. The strong magnetic field dependence of the magnetoresistance and the differences between sheet carrier and 2D carrier density can be attributed to the 3D carriers between the graphene sheet and the SiO₂/Si substrate.     

Hall effect in a martensitic transformation in Ni-Co-Mn-In Heusler alloys

The Hall effect, transverse magnetoresistance, and magnetization of Ni₄₈Co₂Mn₃₅In₁₅ Heusler alloys have been studied at T = 77–300 K in magnetic fields up to 15 kOe. It has been shown that a martensitic transformation is accompanied by a change in the sign of the constant of the ordinary Hall effect, which means a strong change in the electronic spectrum in the martensitic transformation, while the anomalous Hall effect (AHE) constant is positive in both the austenite and martensite phases. In both phases, there are no correlations between the AHE constant and the square of the resistivity, which are characteristic of the side jump mechanism in the AHE theory. In the near vicinity of the martensitic transformation, the field dependences of the Hall resistance are complex and nonmonotonic, indicating a change in the relative concentrations of the austenite and martensite phases in strong fields.     

Low-Temperature anomalies of the Hall coefficient for a magnetic Kondo lattice of CeAl2

The Hall coefficient R _H and magnetoresistance of a magnetic Kondo lattice of CeAl₂ were investigated over a wide temperature range from 1.8 to 300 K in magnetic fields of up to 80 kOe. Analysis of the measured angular dependences R _H(?, T, H) made it possible to separate the contributions of skew scattering and anomalous magnetic scattering to the anomalous Hall effect. The results obtained were compared with the existing theoretical models.     

Galvanomagnetic properties of polycrystalline manganese selenide Gd<Subscript>0.2</Subscript>Mn<Subscript>0.8</Subscript>Se

The electrical and galvanomagnetic properties of the Gd_0.2Mn_0.8Se solid solutions are investigated in zero magnetic field and in a field of 13 kOe in the temperature range of 80–400 K. The negative magnetoresistance below room temperature and hysteresis of the I–V characteristics are found. The change in the magnetoresistance sign and thermopower with increasing temperature is established. The carrier type is determined from the Hall constant; the difference between the thermopower and Hall coefficient signs at high temperatures is established. The experimental data are explained using the model of orbital ordering and spin-orbit interaction.     

Incommensurate superlattice reflections in quasi one dimensional conductors, (MSe4)2I (M=Ta and Nb)

X-ray diffraction and conductivity measurements have been made on (MSE₄)₂I, (M=Ta and Nb). A phase transition of (NbSe₄)₂I was found and the transition temperature T_c was determined to be about 210K by the conductivity measurement. For (TaSe₄)₂I, T_c was about 260K as reported previously. Superlattice reflections due to the formation of charge density wave (CDW) in (TaSe₄)₂I were observed at points $\text{q}\text{?}\text{=(±0.05, ±0.05, ±0.085)}$. The type of CDW of (NbSe₄)₂I is known to be identical to that of (TaSe₄)₂I. Temperature dependence of the threshold electric field of nonlinear conductivity is consistent with the result in previous reports.