Galvanomagnetic Effects Research Articles

Galvanomagnetic Effect and Magnetization Process in CoO/Co/NiFe Film with Antidot Array

The effects of antidot structures of the CoO layer in the CoO/Co/NiFe film were studied by measuring the magnetoresistance (MR) and Hall resistance (HR) of the films. In the MR and the HR, the resistance changes corresponding to the magnetization reversals of the antidot regions were observed, in addition to the main resistance changes caused by the magnetization reversals of the regions coupling with the CoO. This suggests that the domain structure in the Co/NiFe layer can be controlled by the patterned CoO. The magnetization of the covered region showed broad switching compared with that in the uniformly-coupled film because of the magnetostatic interaction caused by the magnetic charges at the boundary between the covered and uncovered regions.

Galvanomagnetic effect and domain wall resistance of ferromagnetic Fe–Ni wire in submicrometer width

The magnetoresistance of an Fe–Ni wire in the presence of a local magnetic field was investigated. The local magnetic field is produced on the Fe–Ni wire by the electric current flowing in a crossing Cu wire. The magnetization reversal of Fe–Ni wire can be controlled by adjusting the strength and sense of the local field. The magnetoresistance is discussed from the viewpoint of the anisotropic magnetoresistance (AMR) effect.

Contact effects on the magnetoresistance of finite semiconductors

We propose a new theoretical method to study galvanomagnetic effects in bounded semiconductors. The general idea of this method is as follows. We consider the electron temperature distribution and the electric potential as consisting of two terms, one of which represents the regular solution of the energy balance equation obtained from the Boltzmann transport equation at steady-state conditions and the Maxwell equation, while the other is the effect of the specimen size that is significant near the contacts (the boundary layer function). With the distribution of the electric potential at the contacts and the electron temperature distribution at the surface of the sample taken into account, we find that the magnetoresistance is different from the one in the standard theory of galvanomagnetic effects in boundless media. We show that, besides the usual quadratic dependence on the applied magnetic field B, the magnetoresistance can exhibit a linear dependence on B under certain conditions. We obtain new formulas for the linear and quadratic terms of the magnetoresistance in bounded semiconductors. This linear contribution of the magnetic field to the magnetoresistance is essentially due to the spatial dependence of the potential at the electric contacts. We also discuss the possibility of obtaining the distribution of the electric potential at the contacts from standard magnetoresistance experiments. Because the applied magnetic field acts differently on carriers with different mobilities, a redistribution of the electron energy occurs in the sample and thus, the Ettingshausen effect on the magnetoresistance must be considered in bounded semiconductors.

Persistent Galvanomagnetic Effects Related to Photo-Quenching Phenomena in Lightly n-type LEC GaAs

We investigated the effect of photo quenching on the galvanomagnetic properties in Te doped n-type GaAs grown by Liquid Encapsulated Czochralski (LEC) process. Although magnetoresistance coefficient and carrier concentration do not change as a function of photo-quenching time at 55 K, the Hall mobility increases with increasing photoquenching illumination time. This results from the photo-quenching of the EL2 centres. On the other hand, the Hall mobility and carrier concentration increase with increasing photoquenching time at 10 K. These are expected because of the acceptor behaviour of reverse contrast (RC) centres. The magnetoresistance coefficients are constant at this temperature. Two different kinds of photo-quenching are once again observed in lightly n-type GaAs at sample temperature of below 65 K and 40 K from a different aspect using galvanomagnetic effects.

Galvanomagnetic Effect of Submicron Exchange-Coupled Co/Ni Wire

The galvanomagnetic effect of an exchange-coupled Co/Ni wire on a submicron scale was investigated by comparing it with the galvanomagnetic effects of single-layered Ni and Co wires. The observed longitudinal magnetoresistance of the Co/Ni wire resembled that of the single-layered Co wire. In the Co/Ni wire, abrupt Hall resistance changes due to the planar Hall effect were observed and were as large as that of the single-layered Co wire. The Hall resistance slopes of the Co/Ni wire due to the extraordinary Hall effect of the Ni layer were also observed, and were smaller than that of the single-layered Ni wire because of the exchange interaction from the Co layer. It was found that, in a low magnetic field, the magnetization processes of both the Ni and Co layers in the Co/Ni wire were almost the same, and were in agreement with that of the single-layered Co wire which is as thick as the Co layer in the Co/Ni wire.

Spin polarization and magneto-Coulomb oscillations in ferromagnetic single-electron transistors

In a single-electron transistor made of ferromagnetic materials, the interplay between the Coulomb blockade and the spin-dependent tunneling causes novel galvanomagnetic effects: the resistance peak at weak magnetic fields due to the spin-valve effect is largely enhanced in the Coulomb blockade regime, and the oscillatory magnetoresistance (Magneto-Coulomb Oscillations, MCO) appears at strong magnetic fields. A model that takes into account the Zeeman effect in ferromagnetic metals explains consistently the characteristics of MCO in various devices.

Gallium-induced defect states in Pb 1− xGe xTe alloys

Galvanomagnetic effects ( B⩽0.1 T, 4.2⩽ T⩽300 K) in n-Pb 1− x Ge x Te (0.04⩽ x⩽0.08) alloys doped with gallium (1.5–3 at%) have been investigated as well as before and after the irradiation with fast electrons ( T≈300 K, E=6 MeV, Φ⩽2.4×10 16 cm −2). Low-temperature activation range on temperature dependencies of the resistivity and the Hall constant has been revealed in the alloys with low initial gallium concentration. Increasing in the gallium content as well as fast-electron irradiation lead to the transition to the metal-type conductivity in the samples. The results were explained under assumption that gallium doping induced the appearance of deep impurity level in the gap of the alloys. The position of the gallium level in depending on the alloy composition was determined.

メゾスコピックスケール十字型磁性細線における電流磁気効果

A cross-shaped Co wire on a mesoscopic scale was fabricated by using electron-beam lithography, and the galvanomagnetic effect was measured at room temperature. Many jumps in the Hall resistance were observed. In order to explain these jumps, exchange interactions with the current and voltage probes were considered, and the Hall resistance was calculated. The calculated result reproduced three jumps in the observed Hall resistance. It was found that the Hall resistance curve of a cross-shaped wire can be controlled by the ratio of the coercive forces of the magnetizations of the probes. The magnetoresistance of a narrow wire with two crossing points was understood by using the present model to calculate the magnetization process.

Galvanomagnetic Effect of Graphite Mixed with Iron and Heat-treated at High Temperatures

Graphite films prepared from aromatic polyimides and a3000°C-treated grafoil were mixed with iron and heat-treated up to 2700°C and/or above. Effects of iron on the transverse magnetoresistance Δρ/ρ0, Hall coefficient RH and residual resistivity ratio RRR of these iron-doped graphite materials have been investigated. RH data imply that only a small amount of iron can substitute into the graphite lattice irrespective of the crystal perfection, and act as acceptors and impure. The heat treatment of graphite materials mixed with iron induces a decrease of Δρ/ρ0 and RRR for the original specimens with RRR>4, but an increase for those with RRR<4. These results indicate that the improvement of crystallinity of graphite materials through a catalytic action of iron becomes predominant for the specimens with RRR<4.

Galvanomagnetic Effects in La2/3D1/3MnO3 (D = Ba, Sr) near Metal–Insulator Transition Point

The magnetoresistance and Hall effect data for polycrystalline samples of La 2/3 D 1/3 MnO 3 (D = Ba, Sr) have been analyzed. It has been revealed that the peculiarities of galvanomagnetic properties take place at the metal-insulator transition temperature which is less than the Curie temperature. The anomalous Hall coefficient is almost three orders of magnitude larger than the normal Hall coefficient. The effects observed have been explained by the shift of the mobility edge.

Galvanomagnetic Effects in La2/3D1/3MnO3 (D = Ba, Sr) near Metal–Insulator Transition Point

The magnetoresistance and Hall effect data for polycrystalline samples of La2/3D1/3MnO3 (D = Ba, Sr) have been analyzed. It has been revealed that the peculiarities of galvanomagnetic properties take place at the metal–insulator transition temperature which is less than the Curie temperature. The anomalous Hall coefficient is almost three orders of magnitude larger than the normal Hall coefficient. The effects observed have been explained by the shift of the mobility edge.

Exchange Interaction from Current and Voltage Probes in Galvanomagnetic Effect in Polycrystal Co Thin Film

The galvanomagnetic effect in a polycrystal Co thin film was investigated by measuring magnetoresistance and Hall resistance. The observed magnetoresistance can be understood in term of the anisotropic magnetoresistance effect using the Stoner-Wohlfarth model. The observed Hall resistance cannot be explained syfficiently by the planar Hall effect using the Stoner-Wohlfarth model. In order to explain the observed Hall resistance, we took the exchange interaction from the current and voltage probes into consideration and numerically calculated the magnetoresistance and the Hall resistance. The calculated results obtained using this model are in reasonable agreement with the experimental results.

A problem with directional derivative in the theory of galvanomagnetic effects

We construct an asymptotics of the solution the Laplace equation in a “long” rectangle with the directional derivative given on its “long sides” and Dirichlet data on its “short sides.” By using the asymptotics, we calculate one of the integral characteristics, namely, the magnetoresistance. We obtain new formulas for the low-magnetic field magnetoresistance.

Theory of magnetic-field-sensitive metal–oxide–semiconductor field-effect transistors

Magnetic-field-sensitive metal–oxide–semiconductor field-effect transistors (MAGFETs) are used as magnetic field sensors. The Hall effect in the high-resistance channel region near the drain ensures a high magnetic field sensitivity of the transistor. In this case, the channel is nonuniform, and this fact presents difficulties when developing a Hall effect theory (the well-known theory of the Hall effect for uniform wafers is now inapplicable). Here, we propose a method that reduces the theory of galvanomagnetic effects in the MAGFETs with nonuniform channels to that for uniform wafers. Basing on this method, as well as on the conformal mapping and the Hall field symmetry, we calculate the Hall electromotive force in MAGFET channels with the Hall taps and split drain. The Hall current in MAGFETs with the split drain and split source is also obtained. It is shown that MAGFET magnetoresistance may be high.

Experimental observation of a new galvanomagnetic effect in YBaCuO single crystals with unidirected twins

The paper presents magnetoresistivity measurements in the vortex liquid phase of YBaCuO single crystals with different angles between unidirected twins and current direction in magnetic fields up to 12 T. Unidirected twin planes are the cause of anisotropic pinning of vortices. In contrast with the measurements of the usual longitudinal magnetoresistance of the isotropic sample which is even with respect to reversal of the direction of the magnetic field, we have observed an additional, odd with respect to reversal of the magnetic field, contribution to the longitudinal resistivity which is due to the presence of unidirected twins in the YBaCuO crystals. A theoretical discussion of the effect is presented.

Pressure-induced insulator-metal transition in electron-irradiated Pb1−x SnxSe (x⩽0.03) alloys

Galvanomagnetic effects (B⩽7 T) in electron-irradiated n-and p-type Pb1−xSnxSe (x⩽0.03) alloys (T≈300 K, E=6 MeV, Φ⩽5.7×1017 cm−2) in the neighborhood of a pressure-induced insulator-metal transition (P⩽18 kbar) are discussed. The field dependences of the Hall coefficient calculated in terms of the two-band model are in satisfactory agreement with the experimental data, and the main parameters of the charge carriers in irradiated alloys are determined. It is shown that there is an increase in the hole concentration in the metallic phase under the action of pressure, associated with the motion of the energy bands at point L of the Brillouin zone, and that electrons overflow from the valence band into the band Et1 of resonance states induced by electron irradiation; the parameters of this band are estimated.

Parameters of defect states in alloys irradiated with electrons

This paper is devoted to the investigation of galvanomagnetic effects in electron-irradiated (, , ) n- and p- alloys in the vicinity of the insulator-metal transition induced by pressure . In the frame of the two-band model, the dependence of the Hall constant on the magnetic field was calculated and found to be in a good agreement with experimental data. The main parameters of charge carriers in irradiated alloys were determined. It was shown that in the metal phase the hole concentration increases under pressure due to the motion of the energy bands at the Brillouin zone L-point and the flow of electrons from the valence band to the radiation defect band . By comparing theoretical and experimental dependences of hole concentration on pressure the parameters of the irradiation-induced defect band were determined.

Magnetic and galvanomagnetic properties of CeMn 2(Ge xSi 1 − x) 2 solid solutions in magnetic fields up to 13 T

The magnetoresistance and magnetization in magnetic fields up to 13 T have been investigated for the CeMn 2(Ge x Si 1 − x ) 2 solid solutions depending on composition. The intermediate valence state, the Kondo lattice state or the stable state of the Ce ions co-exist with the anti-ferromagnetic or ferromagnetic state of the Mn sublattice. For some of samples the Hall effect was measured. The substitution of Si → Ge leads to the increase of the magnetoresistance [R(B) − R(0)]/R(0). At 4.2 K and in a magnetic field of 13 T it changes its value from + 70% for x = 0 to ≤ ∥ ± 5∥ % for x ≥ 0.3. The behaviour of the galvanomagnetic effects is discussed.

Hole boil-off and the magnetoresitance of the semimagnetic semiconductor Hg1−x MnxTe1−y Sey

Galvanomagnetic effects were investigated in gapless and narrow-gap semiconductors of the form Hg1−xMnxTe1−ySey with x=0.03–0.11, y=0.01–0.10 (−150 ρxx), observed at liquid-helium temperatures and in magnetic fields H>10 kOe, is explained in terms of the properties of the energy spectrum of the valence band of semimagnetic semiconductors in quantizing magnetic fields.

Substrate-Induced Strain in Epitaxial Lead Chalcogenides by Galvanomagnetic Effect Rotational Dependence

Substrate-Induced Strain in Epitaxial Lead Chalcogenides by Galvanomagnetic Effect Rotational Dependence