Transverse Magnetoresistance Effect Research Articles

Theoretical Study on Anisotropic Magnetoresistance Effects of Arbitrary Directions of Current and Magnetization for Ferromagnets: Application to Transverse Anisotropic Magnetoresistance Effect

We develop a theory of the anisotropic magnetoresistance (AMR) effects of arbitrary directions of current and magnetization for ferromagnets. Here, we use the electron scattering theory with the $s$--$s$ and $s$--$d$ scattering processes, where $s$ is the conduction electron state and $d$ is the localized d states. The resistivity due to electron scattering is expressed by the probability density of the d states of the current direction. The d states are numerically obtained by applying the exact diagonalization method to the Hamiltonian of the d states with the exchange field, crystal field, and spin--orbit interaction. Using the theory, we investigate the transverse AMR (TAMR) effect for strong ferromagnets with a crystal field of cubic or tetragonal symmetry. The cubic systems exhibit the fourfold symmetric TAMR effect, whereas the tetragonal systems show the twofold and fourfold symmetric TAMR effect. On the basis of the above results, we also comment on the experimental results of the TAMR effect for Fe$_4$N.

Evidence of weak Anderson localization revealed by the resistivity, transverse magnetoresistance and Hall effect measured on thin Cu films deposited on mica

We report the resistivity of 5 Cu films approximately 65 nm thick, measured between 5 and 290 K, and the transverse magnetoresistance and Hall effect measured at temperatures 5 K < T < 50 K. The mean grain diameters are D = (8.9, 9.8, 20.2, 31.5, 34.7) nm, respectively. The magnetoresistance signal is positive in samples where D > L/2 (where L = 39 nm is the electron mean free path in the bulk at room temperature), and negative in samples where D < L/2. The sample where D = 20.2 nm exhibits a negative magnetoresistance at B < 2 Tesla and a positive magnetoresistance at B > 3 Tesla. A negative magnetoresistance in Cu films has been considered evidence of charge transport involving weak Anderson localization. These experiments reveal that electron scattering by disordered grain boundaries found along L leads to weak Anderson localization, confirming the localization phenomenon predicted by the quantum theory of resistivity of nanometric metallic connectors. Anderson localization becomes a severe obstacle for the successful development of the circuit miniaturization effort pursued by the electronic industry, for it leads to a steep rise in the resistivity of nanometric metallic connectors with decreasing wire dimensions (D < L/2) employed in the design of Integrated Circuits.

Angular dependence of magnetoresistance and planar Hall effect in semimetals in strong magnetic fields

The semiclassical transport theory is especially powerful for investigating galvanomagnetic effects. Generally, the semiclassical theory is applicable only in weak fields because it does not consider Landau quantization. Herein, we extend the conventional semiclassical theory by considering Landau quantization through the field dependence of carrier density in semimetals. The extended semiclassical theory is applicable even in strong fields, where Landau quantization is noticeable. Using this new approach, we explain the qualitative change in the angular dependence of transverse magnetoresistance (TMR), anisotropic magnetoresistance (AMR), and planar Hall effect (PHE) in bismuth with an increase in the magnetic field. This unveils the puzzle of nontrivial field-induced changes in TMR, AMR, and PHE observed recently in semimetal bismuth.

Transport Properties of EuNi2Ge2 under High Pressure

Transverse magnetoresistance (MR) and Hall effect have been measured for EuNi2Ge2 single crystals under high pressures up to 2.0 GPa. The compound undergoes a valence transition from a nearly trivalent state to a divalent state with increasing temperature above 1.6 GPa. It was found that the transverse MR of EuNi2Ge2 is negative at low temperatures in the nearly trivalent state, although the compound is nonmagnetic. The origin of the negative MR is discussed. In the temperature dependence of the Hall resistivity ρH, large jumps associated with the valence transition were observed at the valence transition temperature. We also examined the field-induced valence transition by the MR and ρH measurements. A marked change in the Hall coefficient was observed at the valence transition field. Our analyses suggest that the ordinary Hall effect plays a dominant role in the changes in ρH at the valence transition.

Effect of doping with rare-earth elements (Eu, Tb, Dy) on the conductivity of Bi2Te3 layered single crystals

The temperature dependences of the resistivity in the directions parallel and perpendicular to the layer plane in the range of temperatures T = 5–300 K and the Hall and transverse magnetoresistance effects (magnetic fields <80 kOe, T = 5 K) are studied for doped and undoped Bi2Te3 layered single crystals. It is shown that, upon the doping of Bi2Te3 crystals with atoms of rare-earth elements (Eu, Tb, Dy), the resistivity in the directions parallel and perpendicular to the layer plane in Bi2Te3 increases. The increase in the resistivity is caused mainly by a decrease in the charge-carrier mobility because of an increased contribution of charge-carrier scattering at defects to scattering processes. The charge-carrier concentrations and mobilities as well as the Hall factor defined by the anisotropy of the effective masses and by the orientation of ellipsoids with respect to the crystallographic axes are estimated.

Transverse anisotropic magnetoresistance effects in pseudo-single-crystal γ′-Fe4N thin films

Transverse anisotropic magnetoresistance (AMR) effects, for which magnetization is rotated in an orthogonal plane to the current direction, were investigated at various temperatures, in order to clarify the structural transformation from a cubic to a tetragonal symmetry in a pseudo-single-crystal Fe4N film, which is predicted from the usual in-plane AMR measurements by the theory taking into account the spin-orbit interaction and crystal field splitting of 3d bands. According to a phenomenological theory of AMR, which derives only from the crystal symmetry, a cos 2θ component (C2tr) exists in transverse AMR curves for a tetragonal system but does not for a cubic system. In the Fe4N film, the C2tr shows a positive small value (0.12%) from 300 K to 50 K. However, the C2tr increases to negative value below 50 K and reaches to -2% at 5 K. The drastic increasing of the C2tr demonstrates the structural transformation from a cubic to a tetragonal symmetry below 50 K in the Fe4N film. In addition, the out-of-plane and in-plane lattice constants (c and a) were precisely determined with X-ray diffraction at room temperature using the Nelson-Riely function. As a result, the positive small C2tr above 50 K is attributed to a slightly distorted Fe4N lattice (c/a = 1.002).

The effect of magnetic field on resistivity of Hg0.89Mn0.11Te in different temperature range

The resistivity of Hg0.89Mn0.11Te has been measured by the superconducting quantum interference device magnetometer in the temperature range from 5 to 200 K under the applied magnetic field of 1, 2, 4 and 6.5 Tesla, respectively, compared with that of no-magnetic field. The results show that the resistivity increases with increase applied magnetic field at higher temperature from 80 to 200 K, but decreases at lower temperature from 5 to 25 K. There exists a transitive range from 25 to 80 K, where the variation of the resistivity shows different tendencies depending on the strength of magnetic field. Maximum difference of resistivity under 6.5 Tesla from that without magnetic field in the temperature range from 30 to 200 K is only about 5 Ω·cm, but it increases up to 3 orders of magnitude at 5 K. The analysis shows that the variation of resistivity of Hg0.89Mn0.11Te under the magnetic field is the algebraic sum of the transverse direction magnetoresistance effect and the sp-d exchange interaction effect. TDRME plays major role in the high temperature range. However, with the decrease of temperature, the effect of sp-d EI on the resistivity gradually exceeds that of the transverse direction magnetoresistance effect through the transitive range, and becomes the dominant effect in the temperature range from 5 to 25 K, which leads to the dramatic decrease of resistivity.

Magnetotransport behavior of silver-rich silver selenide polycrystalline synthesized by a chemical method

Abstract A series of polycrystalline silver selenide (Ag2+δSe) were synthesized by a chemical method combined with traditional solid-state one. The composition of Ag2+δSe was adjusted by the raw material ratio of silver nitrate to selenium powder. The results of XRD and SEM showed the occurrence of excess Ag within the matrix. Magnetotransport behavior varied with the amount of excess Ag (δ). Among these compositions, polycrystalline Ag2.215Se displayed a maximum size of transverse magnetoresistance (TMR) effect and a lowest crossover field Hc (even close to zero at 77 K). Combined the results of morphology, zero-field resistivity and optical band-gap, the mechanism of the linear TMR was thought to be a combination of quantum effect and classical one.

Two-step synthesis of silver selenide semiconductor with a linear magnetoresistance effect

A two-step synthesis method for polycrystalline β-silver selenide (β-Ag2Se) was developed. In the first step, nanopowder was prepared using a chemical conversion method at room temperature. In the second step, the nanopowder was compressed and then the bulk Ag2Se was fabricated by the solid-state sintering process. The crystalline phase and morphology were examined. The results showed that β-Ag2Se was fast fabricated at room temperature. The dense polycrystalline Ag-rich Ag2Se was synthesized successfully at 450 °C for 0.5 h under Argon flow. For the polycrystalline, the electronic properties and transverse magnetoresistance (TMR) in a pulsed magnetic field were investigated. The samples displayed n-type semiconducting behaviors and a critical temperature with a broaden temperature range of 140–150 K. Also, it presented a positive and nearly linear dependence on magnetic field H at H ≥ Hc (crossover field) ranging from 2 to 20 T. Moreover, the linear dependence of TMR at strong field was non-saturating up to 35 T. Combining with the observation of morphology, it is thought that this unusual TMR effect was caused by slightly excess Ag. This new synthesis method provided a potential route to synthesize nonstoichiometric silver selenide.

Large magnetoresistance effect in InN epilayers

We report on the large nonsaturated transverse magnetoresistance (TMR) effect in InN films grown by plasma-assisted molecular-beam epitaxy. It is proved that the origin of the TMR effect in InN epilayers is the presence of spontaneously formed In nanoparticles. The effect of the In nanoparticles on the transport properties of the InN films is discussed in detail, accompanied by supporting theoretical calculations. The role of electronic parameters of the InN semiconductor matrix as well as the size and amount of In nanoparticles, which govern the magnitude of the TMR effect, has been determined. The negative TMR effect observed in Mg-doped InN films is also considered within the same metal-semiconductor composite model. It is proposed that high Mg concentration leads to the formation of specific modification of size and arrangement of the In inclusions.

Effect of low nitrogen concentrations on the electronic properties ofInAs1−xNx

We report cyclotron resonance (CR), transverse magnetoresistance (MR), and Hall effect studies of a series of $n$-type ${\text{InAs}}_{1\ensuremath{-}x}{\text{N}}_{x}$ epilayers grown on GaAs with $x$ up to 1%. The well-resolved CR absorption lines, the classical linear MR, Shubnikov--de Haas magneto-oscillations, and negative MR revealed in our experiments provide a means of probing the effect of the N atoms on the electronic properties of this alloy system and reveal qualitative differences compared to the case of the wider gap III-N-V compounds, such as ${\text{GaAs}}_{1\ensuremath{-}x}{\text{N}}_{x}$. In ${\text{GaAs}}_{1\ensuremath{-}x}{\text{N}}_{x}$ electron localization by N levels that are resonant with the extended band states of the host crystal act to degrade the electrical conductivity at small $x$ $(\ensuremath{\sim}0.1%)$. These phenomena are significantly weaker in ${\text{InAs}}_{1\ensuremath{-}x}{\text{N}}_{x}$ due to the smaller energy gap and higher energy of the N levels relative to the conduction band minimum. In ${\text{InAs}}_{1\ensuremath{-}x}{\text{N}}_{x}$ the electrical conductivity retains the characteristic features of transport through extended states, with electron coherence lengths (${l}_{\ensuremath{\varphi}}\ensuremath{\sim}100\text{ }\text{nm}$ at 2 K) and electron mobilities ($\ensuremath{\mu}=6\ifmmode\times\else\texttimes\fi{}{10}^{3}\text{ }{\text{cm}}^{2}\text{ }{\text{V}}^{\ensuremath{-}1}\text{ }{\text{s}}^{\ensuremath{-}1}$ at 300 K) that remain relatively large even at $x=1%$.

Temperature Dependence of Magnetoresistance and Hall Effect for Ho Doped n-Type InSe

Magnetoresistance and Hall effect measurements were carried out for Ho doped n-InSe (n-InSe:Ho) sample in the temperature range 10–340 K, in which the sample exhibits transverse magnetoresistance (MJ⊥B) and longitudinal magnetoresistance (MJ//B) effect. The fit to a temperature power law T - β gives MJ⊥B ∝ T - 1.07 and MJ//B ∝ T - 1.11 in the range 10–340 K for n-InSe:Ho. The transverse magnetoresistance coefficient of InSe:Ho in the temperature range 10–340 K is much greater than that of the reference n-InSe sample. As the temperature increases, the carrier concentration in the n-InSe:Ho sample increases between 10–340 K. Impurity energy levels calculated from ln(p/T 3/2) vs 103/T plot for n-InSe:Ho in the range 10–40 K, 40–240 K and 260–340 K are Ec-69 meV, Ec-264 meV and Ec-568 meV, respectively. The electron Hall mobility of the n-InSe:Ho sample decreases, as µH ∝ T - 2.35 for 140–340 K. The Hall mobility and the carrier concentration of the n-InSe:Ho sample increase with increasing temperature in the range 10–340 K.

Magnetic and transport properties of sub-micron ferromagnetic wires

Submicron Co wires with a variable width in the range from 0.2 to 2 /spl mu/m and paired Co disks with a variable diameter in the range from 0.4 to 5 /spl mu/m were prepared to investigate the magnetoresistance effect in association with the domain wall formation. A clear change in resistivity due to traversing domain wall along the wire is observed for all the widths in both longitudinal and transverse magnetoresistance effects. The domain wall gives a negative contribution to the magnetoresistance effect. Longitudinal magnetoresistance effects of paired Co disks show an anomalous increase in low fields below 20 kOe due to the peculiar vortex structure stabilized in the disk.

Quantum galvanomagnetic effects in the organic metal α-(BEDT-TTF)2TlHg(SCN)4

The transverse magnetoresistance and Hall effect of the organic metal {alpha}-(BEDT-TTF){sub 2}TlHg(SCN){sub 4} have been studied in static magnetic fields of up to 33 T applied perpendicular to the highly conducting planes. The Hall resistivity is found to exhibit strong oscillations caused by the coexistance of quasi-one-dimensional and quasi-two-dimensional states in the electronic system. In higher quality crystals, plateaulike features appear at magnetic fields above {approximately}30 T, which are consistent with recent claims of the quantum Hall effect in this material. {copyright} {ital 1997} {ital The American Physical Society}

Magnetic-field-induced phase transition and sliding motion of charge-density waves in η-Mo4O11scrystals

Transverse magnetoresistance and Hall effect of the charge-density-wave (CDW) material \ensuremath{\eta}-${\mathrm{Mo}}_{4}$ ${\mathrm{O}}_{11}$ have been measured at 4.2 K (second CDW state) by dc and ac methods over the frequency range 50--500 kHz in pulsed magnetic fields up to 40 T. These quantities are both reversible and frequency independent for a low-field sweep up to near 10 T (=${\mathrm{H}}_{\mathrm{c}}$ ), beyond which an appreciable frequency-dependent hysteresis effect appears. The Cole-Cole plots of the real versus imaginary parts of the magnetoresistance at high magnetic fields show a monodispersion. The magnetic-field dependence of the real part of the ac Hall resistivity shows interesting behaviors, peaking near ${\mathrm{H}}_{\mathrm{c}}$ , followed by a decrease with H and a leveling off at high fields, while the imaginary components are very small and less frequency dependent. Using a multicarrier model consisting of the remaining and nested electron and hole bands, we have performed computer simulations for these dc and ac magnetotransport quantities, in satisfactory agreement with the observations. We have taken into account (1) the Zeeman effect for two types of the remaining hole and electron bands, (2) the CDW-gap narrowing of the nested electron and hole bands, (3) magnetic-field-induced CDW-to-normal phase transition in part of these nested bands, and (4) the magnetic-field-induced 'CDW oscillation' around some mean position of the CDW condensates (or thermal excitation of the CDW phasons over a pinning potential), according to the existing CDW model.

Temperature dependence of galvanomagnetic properties for Er-doped and undoped n-type InSe

The magnetoresistance and the Hall-effect measurements in undoped n-InSe (InSe) and Er-doped InSe (InSe:Er) samples in the temperature range 10–340 K were carried out. The InSe sample and the InSe:Er sample exhibit a null transverse magnetoresistance effect for T≳160 and T≳140 K, respectively, and a zero longitudinal magnetoresistance effect for T≳160 and T≳100 K, respectively. As the temperature increases, the carrier concentration obtained from the Hall-effect measurements in the InSe sample increases up to 40 K, decreases in the range 40–100 K, and increases for T≳100 K, although the carrier concentration in the InSe:Er sample increases up to 300 K. In the same samples, the Hall mobility of the InSe sample increases up to 80 K and obeys to μH∝T−1.86 for T≳80 K, although the Hall mobility of the InSe:Er sample decreases up to 340 K and obeys to μH∝T−1.51 for T≳80 K. The electrical conductivity, which is proportional to a product of the Hall mobility and the carrier concentration, of the InSe sample and the InSe:Er sample decreases with increasing temperature for T≳60 and T≳100 K, respectively.

Effect of Pressure on the Charge Density Wave Transitions in η‐Mo4O11 Crystal

AbstractElectrical resistivity ϱ versus temperature T over 4.2 to 300 K under hydrostatic pressures up to 1.2 GPa, transverse magnetoresistance, and Hall effect at 4.2 K and constant pressure are measured for a quasi‐two‐dimensional crystal of monoclinic η‐Mo4O11. Semiempirical analysis of the ϱ−T curves below the charge density wave (CDW) transition temperatures Tc1 and Tc2 shows that the temperature dependences of the CDW gap energies δ1(T) and δ2(T) follow a single universal curve, independent of applied pressures. The Shubnikov‐de Haas oscillations are also observed in these transport quantities, from which the effect of pressure on the nature of Fermi surfaces of holes and/or electrons associated with the CDW transitions is discussed qualitatively.

Cross-over instability and chaos of hysteretic I–V curve during impurity avalanche breakdown in n-GaAs under longitudinal magnetic field

Magnetic field effects on the hysteretic I–V curve caused by low-temperature impurity avalanche breakdown at 4.2 K have been investigated in high-purity n-GaAs. Main results for the transverse magnetic fields are shifts of the hysteresis towards higher breakdown voltages due to transverse magnetoresistance effect. Under the longitudinal magnetic fields, the holding voltage of the hysteresis moves towards higher voltages, while the breakdown voltage does not show any significant shifts. With B ⪆ 47 mT, the holding voltage exceeds the breakdown voltage, and eventually the cross-over current instability and chaos have been observed.

Magnetoresistance and de Haas-van Alphen effect in CeIn3

We have measured the transverse magnetoresistance and de Haas-van Alphen (dHvA) effect in the antiferromagnetic Kondo lattice substance CeIn3. The magnetoresistance increases in the wide field region, suggesting a compensated metal. Open orbits are found along the <110> and <112> directions. We have detected one dHvA branch which corresponds to the electron sheet of sixth band in LaIn 3, centered at the π point.

Magnetoresistance and de Haas-van Alphen Effect in CeIn3

We have measured the transverse magnetoresistance and de Haas-van Alphen (dHvA) effect in the antiferromagnetic Kondo substance CeIn 3 . The magnetoresistance increases in all field directions, suggesting that this compound is a compensated metal. We have detected one dHvA branch which corresponds to the electron Fermi surface in the sixth band of LaIn 3 , centered at the Γ point. The dHvA frequencies (cyclotron masses) at the <100> and <111> directions are 3.20×10 7 Oe (2.02m 0 ) and 2.95×10 7 Oe (2.88m 0 ), respectively.