Transverse Magnetoresistance Measurements Research Articles

Weak Antilocalization Tailor-Made by System Topography in Large Scale Bismuth Antidot Arrays.

Using a two-carriers model and the Hikami-Larkin-Nagaoka (HLN) theory, we investigate the influence of large area patterning on magnetotransport properties in bismuth thin films with a thickness of 50 nm. The patterned systems have been produced by means of nanospheres lithography complemented by RF-plasma etching leading to highly ordered antidot arrays with the hexagonal symmetry and a variable antidot size. Simultaneous measurements of transverse and longitudinal magnetoresistance in a broad temperature range provided comprehensive data on transport properties and enabled us to extract the values of charge carrier densities and mobilities. Weak antilocalization signatures observed at low temperatures provided information on spin-orbit scattering length ranging from 20 to 30 nm, elastic scattering length of approx. 60 nm, and strong dependence on temperature phase coherence length. We show that in the absence of antidots the charge carrier transport follow 2-dimensional behavior and the dimensionality for phase-coherent processes changes from two to three dimensions at temperature higher than 10 K. For the antidot arrays, however, a decrease of the power law dephasing exponent is observed which is a sign of the 1D-2D crossover caused by the geometry of the system. This results in changes of scattering events probability and phase coherence lengths depending on the antidot diameters, which opens up opportunity to tailor the magnetotransport characteristics.

Magneto-transport properties in fcc ytterbium

Electron-hole compensation in a heavy rare-earth, ytterbium (Yb), was investigated by room-temperature galvanomagnetic measurements and a two-band model analysis. Face-centered cubic (fcc) Yb films were prepared by a molecular-beam technique. Transverse magnetoresistance (MR) and Hall resistivity (HR) measurements were performed on the fcc Yb film at room temperature. Transverse MR showed a quadratic behavior under magnetic fields up to ±5 T, whereas the HR had linear characteristics and a positive Hall coefficient. The experimental results are quantitatively explained by a two-band model with nearly identical carrier density (∼1×1021 cm−3) and mobility (∼70–80 cm2 V−1 s−1) of electrons and holes. The positive Hall coefficient observed is explained by a slightly greater hole density and/or mobility compared with those of electrons.

Magnetotransport properties of noncentrosymmetric CaAgBi single crystal

We report on the single crystal growth and transport properties of a topological semimetal CaAgBi which crystallizes in the hexagonal ABC-type structure with the non-centrosymmetric space group P63mc (No. 186). The transverse magnetoresistance measurements with current in the basal plane of the hexagonal crystal structure reveal a value of about 30% for I∥[10̄0] direction and about 50% for I∥[1̅10] direction at 10 K in an applied magnetic field of 14 T. The magnetoresistance shows a cusp-like behavior in the low magnetic field region, suggesting the presence of weak antilocalization effect for temperatures less than 100 K. The Hall measurements reveal that predominant charge carriers are p-type, exhibiting a linear behavior at high fields. The magnetoconductance of CaAgBi is analyzed based on the modified Hikami–Larkin–Nagaoka model. Our first-principle calculations within a density-functional theory framework reveal that the Fermi surface of CaAgBi consists of both the electron and hole pockets and the size of the hole pocket is much larger than electron pockets suggesting the dominant p-type carriers in accordance with our experimental results.

Studies on Shubnikov-de Hass oscillations in p-Sb2Te2Se topological insulator

Transverse and longitudinal magneto-resistance measurements on Sb2Te2Se (STS)topological insulator single crystals are reported. Electrical resistivity (ρxx) on STS measured in the temperature range of 300−3 K showed a metallic behavior. Hall measurements indicate that the carriers are p-type and its temperature dependence exhibits an increasing behavior as the temperature decreases. The magneto-transport behavior exhibits distinct Shubnikov-de Hass (SdH) oscillations only when the magnetic field is perpendicular to the sample surface. The SdH oscillations have been analyzed using Lifshitz-Kosevich (LK) equation, and the material parameters have been derived from the fit. The value of the Berry phase (β) determined from a Landau level fan diagram is found to be 0.77. Strictly linear Hall data in conjunction with single frequency SdH oscillations shows that the observed quantum phenomena presumably stems from the surface states.

Angle-dependent magnetoresistance and quantum oscillations in high-mobility semimetal LuPtBi

The recent discovery of ultrahigh mobility and large positive magnetoresistance in the topologically non-trivial half-Heusler semimetal LuPtBi provides a unique playground for studying exotic physics and significant perspective for device applications. As an fcc-structured electron–hole-compensated semimetal, LuPtBi theoretically exhibits six symmetrically arranged anisotropic electron Fermi pockets and two nearly-spherical hole pockets, offering the opportunity to explore the physics of Fermi surfaces with simple angle-related magnetotransport properties. In this work, through angle-dependent transverse magnetoresistance measurements, in combination with high-field SdH quantum oscillations, we aimed to map out a Fermi surface with six anisotropic pockets in the high-temperature and low-field regime, and furthermore, identify a possible magnetic field driven Fermi surface change at lower temperatures. Reasons account for the Fermi surface change in LuPtBi are discussed in terms of the field-induced electron evacuation due to Landau quantization.

One-dimensional edge transport on the surface of cylindrical BixTe3−ySey nanowires in transverse magnetic fields

The geometry of topological insulators (TIs) has a major impact on the magnetoelectric band structure of their surface states. Here, we investigate the surface states of cylindrical TI bismuth telluride selenide nanowires with three different diameters, by parallel and transverse magnetoresistance (MR) measurements. In parallel configuration, we observe Aharonov-Bohm oscillations as well as weak antilocalization, indicating two-dimensional TI surface states. In transverse magnetic fields, we observed MR oscillations that are non-linear against the reciprocal of the magnetic field and thus cannot be explained by two- or three-dimensional states. Instead, our transport data analysis reveals that these MR oscillations are the consequence of one-dimensional edge channels at the nanowire surface that form due to the projection of the external magnetic field on the cylindrically curved surface plane in high magnetic fields. Our observation provides an exotic class of surface states that might be used for electronic and spintronic devices.

Low-temperature resistivity, magnetoresistance, and domain-wall resistance of highly pure single- and polycrystalline iron

On a set of 12 bulk and highly pure [residual resistance ratio (RRR) up to 6000] iron single crystals with different crystallographic orientation and on polycrystalline material the ``hidden'' basic resistivity $\ensuremath{\rho}(T,B\ensuremath{\rightarrow}0)$ and magnetoresistive effects (anisotropic magnetoresistance, longitudinal and transverse Lorentz resistance) are quantitatively disentangled. The temperature-dependent basic resistivity for $T\ensuremath{\le}30\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ follows a $\ensuremath{\Delta}\ensuremath{\rho}(T,B\ensuremath{\rightarrow}0)=a{T}^{2}+b{T}^{5}$ law, proving that electron-electron and electron-phonon scattering (with a resistive Debye temperature ${\ensuremath{\Theta}}_{\mathrm{R}}\ensuremath{\cong}450\phantom{\rule{0.28em}{0ex}}\mathrm{K}$) are dominant also in iron, similar to nonferromagnetic transition metals. Here the crystal-orientation dependence of the intrinsic longitudinal magnetoresistance in the single-domain state could be quantitatively evaluated in accordance with the symmetry of the Fermi surface. The transverse magnetoresistance (TMR) turns out to be the sum of the so-called ``two-band conduction term'' and the unboundedly growing TMR term in compensated metals. It is proven that the second term is not restricted to the high-field limit (as usually discussed up to now) but acts down to lowest TMR or ${\ensuremath{\omega}}_{\mathrm{C}}\ensuremath{\tau}$ values. This conclusion is verified by TMR measurements on highly pure molybdenum single crystals (RRR \ensuremath{\cong} 100 000). Supported by Kerr microscopy, a small positive domain wall resistance (DWR) could be isolated from the dominating negative DWR in the multidomain state of iron, resulting in a relation of larger than 5:1 for the electrons to pass a domain wall with spin tracking compared to scattering with spin conservation.

In-Plane Magnetoresistance Obeys Kohler’s Rule in the Pseudogap Phase of Cuprate Superconductors

We report in-plane resistivity (ρ) and transverse magnetoresistance (MR) measurements for underdoped HgBa(2)CuO(4+δ) (Hg1201). Contrary to the long-standing view that Kohler's rule is strongly violated in underdoped cuprates, we find that it is in fact satisfied in the pseudogap phase of Hg1201. The transverse MR shows a quadratic field dependence, δρ/ρ(0)=aH(2), with a(T)∝T(-4). In combination with the observed ρ∝T(2) dependence, this is consistent with a single Fermi-liquid quasiparticle scattering rate. We show that this behavior is typically masked in cuprates with lower structural symmetry or strong disorder effects.

Electrical transport properties of CuS single crystals

Electrical resistivity, transverse magnetoresistance and thermoelectric power measurements were performed on CuS high quality single crystals in the range 1.2–300 K and under fields of up to 16 T. The zero field resistivity data are well described below 55 K by a quasi-2D model, consistent with a carrier confinement at lower temperatures, before the transition to the superconducting state. The transverse magnetoresistance develops mainly below 30 K and attains values as large as 470% for a 16 T field at 5 K, this behaviour being ascribed to a band effect mechanism, with a possible magnetic field induced DOS change at the Fermi level. The transverse magnetoresistance shows no signs of saturation, following a power law with field Δρ/ρ(0) ∝ H1.4, suggesting the existence of open orbits for carriers at the Fermi surface. The thermoelectric power shows an unusual temperature dependence, probably as a result of the complex band structure of CuS.

Coexistence of Dirac-cone states and superconductivity in iron pnictide Ba(Fe1−xRuxAs)2

The Ru doping effect on the Dirac-cone states is investigated in iron pnictide superconductors Ba(Fe${}_{1\ensuremath{-}x}$Ru${}_{x}$As)${}_{2}$ using transverse magnetoresistance (${R}_{\mathrm{M}}$) measurements as a function of temperature. The linear development of ${R}_{\mathrm{M}}$ against magnetic field $B$ is observed for $x=0$--0.244 at low temperatures below the antiferromagnetic transition. The $B$-linear ${R}_{\mathrm{M}}$ is interpreted in terms of the quantum limit of the Dirac-cone states by using the model proposed by Abrikosov. An intriguing evidence is shown that the Dirac-cone state persists on the electronic phase diagram where antiferromagnetism and superconductivity coexist.

Origin of large positive magnetoresistance in permalloy(Ni 0.8Fe 0.2)–graphite granular composites

We report the magnetoresistance (MR) of ball milled nano-granular (Ni 0.8Fe 0.2) x C 100− x ( x = 0–50%) composites. Structural characterization has been carried out using X-ray diffraction and TEM measurements; while the electrical transport measurements were carried out by conventional four probe technique. Longitudinal ( L) and transverse ( T) magnetoresistance measurements were performed at room temperature upto 50 kOe magnetic field. Magnetic measurements on the composites show all the composites to be ferromagnetic. Although magnetic properties show significant changes in magnetization values, comparable variations could not be detected in MR measurements, suggesting the origin of large positive magnetoresistance is non-magnetic. The existing models for the electron transport behavior fail to explain the H 3/2 dependence of the MR. We have attempted to explain the origin of large positive MR values in these composites.

Negative magnetoresistance in transverse and longitudinal magnetic fields in Bi nanowires

In this work the measurements of longitudinal (LMR) and transverse magnetoresistance (TMR) in Bi wires with 50<d<500 nm in the interval 4.2 - 300 K and magnetic field up to 14 T were carried out. Was shown that, the maximum on LMR at H||I is suppressed due to quantum size effect. For the first time it was found that the field dependence of TMR R(H) at I⊥H) in Bi wires with d<80 nm contains the negative region R(H) > R0 at T<5 K. This result was unexpected, because it is known that in bulk Bi samples the "giant" increase of magnetoresistance in the case H⊥I is observed. We calculate the conductivity of nanowires in longitudinal and transverse magnetic fields on the basis of the Cubo formula for the conductivity. We use the model of quantum wires with a parabolic potential in the plane orthogonal to the axis of the size-quantized system. According to the model of such TMR and LMR were experimentally observed in the Bi quantum wires (QW) with d<80nm.

Semiclassical electronic transport in MnAs thin films

Magneto-transport experiments have been recently performed on MnAs thin films. Hall effect and transverse magnetoresistance measurements have shown interesting and, until now, unknown results. For instance, the transverse magnetoresistance shows no saturation in the presence of very high magnetic fields. In order to understand the contribution of the electronic band structure to the non-saturating magnetoresistance, we perform ab initio calculations, using the Wien2K code and analyze the magneto-transport properties within the semiclassical approximation. We show that non-saturation may be due to the presence of open orbits on the majority Fermi surface.

Magnetotransport properties in near-stoichiometric hydride films of YH2+δ under weak fields

We have investigated the basic characteristics of mobile carriers in as-deposited thin films of hexagonal-close-packed Y and hydrogenated films of face-centered-cubic YH2+δ. Hall resistance and transverse magnetoresistance measurements were carried out under magnetic fields of up to 1 T at room temperature. The Hall coefficient in YH2+δ showed a minimum value of ∼5×10−12 m3/C when the δ value reached ∼−0.1, in accordance with the δ dependence of resistivity reported previously. Quantitative analysis based on the present measurements revealed that YH2+δ is a compensated metal whose carrier density and mobility were determined to be ∼1.4×1027 (∼1.9×1027) m−3 and ∼3.5×10−3 (∼3.1×10−3) m2 V−1 s−1, respectively, for δ=0.04(−0.03) for both electrons and holes. These carrier parameters were found to account concurrently for the reflection spectral line shapes observed. The compensation observed in YH2+δ is at variance with a simple criterion used previously [E. Fawcett and W. A. Reed, Phys. Rev. 131, 2463 (1963)].

Galvanomagnetic properties of super and substoichiometric yttrium dihydrides

Hall resistance and transverse magnetoresistance measurements were performed under magnetic fields of up to 5 T to reveal the basal characteristics of mobile carriers in near-stoichiometric dihydrides YH 2 + x ( x = - 0.23 and 0.04). Unusually small Hall coefficients, e.g. 9.0 × 10 - 12 m 3 / C for x = - 0.23 , were observed, leading us to the tentative conclusion that f.c.c. YH 2 + x is a compensated metal in which electrons and holes have nearly equal carrier density. In addition, carrier mobility was revealed to be nearly equal for electrons and holes, with a difference of less than 7%.

Size effects under a strong magnetic field: transverse magnetoresistance of thin gold filmsdeposited on mica

We report measurements of transverse magnetoresistance where the signal can beattributed to electron–surface scattering, together with measurements of the surfaceroughness of the films on an atomic scale. The measurements were performed with ascanning tunnelling microscope (STM) on four thin gold films evaporated onto mica. Themagnetoresistance exhibits a marked thickness dependence: at 4 K and 9 T is about 5% forthe thinner (69 nm) film, and about 14% for the thicker (185 nm) film. Sondheimer’stheory provides an accurate description of the temperature dependence of theresistivity, but predicts a magnetoresistance one order of magnitude smaller thanthat observed at 4 K. Calecki’s theory in the limit of small roughness correlationlength, predicts a resistivity two orders of magnitude larger than observed at 4 K.

Non‐magnetic anion substitution in (TMTSF) 2 ClO 4 : consequences on superconductivity

The influence of non magnetic impurities on the superconductivity of the quasi-one dimensional organic conductor (TMTSF)2ClO4 is investigated. Non magnetic impurities are added through the substitution of up to 3% of the ClO4 anions by ReO4 anions. Transverse resistivity and magnetoresistance measurements were performed in the superconducting state down to 100 mK. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Crystal-field Γ8-like State in Magnetically Ordered Phases of CeP: Its Anisotropy and Influence on Electronic Structure via High-Field Magnetotransport Measurements

Although the crystal-field ground state in the paramagnetic phase of CeP is Γ 7 , part of cerium ions take a Γ 8 -like state in magnetically ordered phases and regular arrangements of the Γ 7 and Γ 8 -like moments constitute magnetic structures. We have performed transverse magnetoresistance measurements up to 32 T for selected field directions and have determined phase boundaries related to the appearance of the Γ 8 -like state for each field direction. The result reveals the extreme uniaxial anisotropy that the Γ 8 -like moment is strongly bound to the [001] axis. We have also determined the field-orientation dependence of phase transitions connected with the rearrangement of the Γ 7 moment via ac susceptibility measurements. The analysis of the angular dependence indicates that the Γ 7 moment prefers the [001] direction only weakly probably due to the exchange field from neighboring Γ 8 moments. The resistivity exhibits a sharp decrease on the appearance of the Γ 8 -like state. Besides, Hall effect mea...

Magnetic properties of the dense Kondo system CeB 6 in high magnetic fields

This work reports on the phase diagram study of the dense Kondo system CeB 6 by means of magnetization ( M) and transverse magnetoresistance (MR) measurements in magnetic fields ( B) to 18 T, in the temperature ( T) range from 1.8 to 40 K. The zero field resistivity displays Kondo behavior in the paramagnetic P-phase, while two discontinuities at low T were observed at T Q≈3.5 K and T N≈2.3 K, the boundaries of the antiferro-quadrupolar (AFQ), and antiferromagnetic (AF) phases, respectively. The isothermal transverse MR is large and negative at low T, and it shows a distinct feature when the P–AFQ line of the B– T phase diagram is crossed. Similarly, the M vs. B curves at low temperatures show upward discontinuities at the phase boundary. Both the features in MR and M at the P–AFQ line correlate well in T, revealing the gradual increase of the T for the onset of AFQ ordering with B. No evidence for reentrant behavior could be observed in fields to 18 T.

Magnetoresistance and magnetic susceptibility in CeNiSn

We have studied a metamagnetic-like anomaly in CeNiSn via measurements of transverse and longitudinal magnetoresistance (MR) and AC magnetic susceptibility ( χ) in a wide range of temperature T, magnetic field B, and pressure p, i.e., 0.05 K⩽ T ⩽0.9 K , 0⩽B ⩽20 T , and 0⩽p ⩽10 kbar . We identify five field regions in which both MR and χ exhibit anomalous behavior, i.e., distinct deviation from monotonous variation as a function of B. The disparate pressure dependence of each regime cannot be explained by the pressure variation of a single parameter, viz., the Kondo temperature, and suggests that the metamagnetic-like anomaly in CeNiSn is a combination of anomalies of different origins.