High-field Hall Research Articles

Longitudinal Hall effect in Terfecohan thin films with perpendicular magnetic anisotropy

Longitudinal extraordinary Hall Effect (LEHE) of magnetic Tb(Fe 0.55Co 0.45) 1.5 (known as Terfecohan) thin films with perpendicular magnetic anisotropy has been investigated as a function of both the intensity of applied magnetic fields and the angle α between the applied field and film normal directions. The Hall voltage loops exhibit a parallelogram shape, which is almost similar to those of the perpendicular magnetization. The high-field Hall voltage susceptibility is positive at α=0. Its value decreases with increasing α and changes in sign at α m=20°, which is considered as the easy magnetizable direction of the film. This finding is comparable with those obtained from the magnetization, magnetic force microscopy (MFM) and conversion electron Mössbauer spectra (CEMS) measurements. The obtained LEHE behaviors are rather promising for applications such as magnetic recording heads and magnetic field detectors, where a large output signal is required at low magnetic fields.

High-Field Fractional Quantum Hall Effect in Optical Lattices

We consider interacting bosonic atoms in an optical lattice subject to a large simulated magnetic field. We develop a model similar to a bilayer fractional quantum Hall system valid near simple rational numbers of magnetic flux quanta per lattice cell. Then we calculate its ground state, magnetic lengths, fractional fillings, and find unexpected sign changes in the Hall current. Finally we study methods for detecting these novel features via shot noise and Hall current measurements.

Hall effect measurements in the heavy-fermion system [formula omitted

Hall effect measurements have been conducted on high-quality single crystals of the heavy-fermion superconductor CeCoIn 5 . The anomalous Hall contribution is negligible in the investigated temperature range from 0.05 to 5 K. The measured Hall resistivities ρ xy show a noticeable change in slope between the low-field (initial Hall coefficient) and the high-field region. In the superconducting regime, T < 2.3 K , Hall measurements are restricted to high magnetic fields H > H c 2 , the upper critical field of superconductivity. The high-field Hall coefficient is almost constant for temperatures down to 250 mK. At T ⩽ 250 mK , an additional change in curvature of ρ xy vs. H is observed.

Magnetoresistance and Hall effect measurements of Ni to 6 GPa

High field magnetoresistance (MR) and Hall effect measurements have been conducted on modular Ni 0.985O 0.015 thin film samples in the diamond anvil cell between 280 and 316 K at applied magnetic fields up to 6 T and at pressures up to 6 GPa. The magnetic resistivity above the technical saturation of the magnetization is found to be negative, linear and nonsaturating while the magnitude of the field derivative, 0.010 – 0.018 μ Ω cm T - 1 , increases with temperature and decreases with pressure. The decrease in the MR is attributed to spin wave damping of electron magnon scattering processes at high fields and the zero temperature magnon mass, 535(49) meV Å 2 at 1.1 GPa, is found to be a slightly increasing function of pressure. Hall effect measurements indicate that skew scattering becomes increasingly important with pressure. Resistivity measurements at zero applied field, normalized to 1.7 GPa, yield a pressure derivative of - 0.018 ( 1 ) GPa - 1 . The effects of pressure and oxygen on the density of states (DOS) at the Fermi level are investigated using total energy electronic band structure calculations and reveal that the DOS of Ni 0.985O 0.015 increases with pressure but remains significantly less than for Ni at 10 GPa. The average magnetic moment of Ni 0.985O 0.015 decreases from 0.675 μ B at 0 GPa to 0.648 μ B at 10 GPa. The magnon mass and magnetic moment are increasing and decreasing functions of pressure, respectively. These effects dominate over the increase in the DOS at the Fermi level and, correspondingly, the field derivative of the magnetic resistivity is found to decrease relative to zero pressure measurements.

Thickness dependence of Hall transport inNi1.15Mn0.85Sbthin films on silicon

Highly spin polarized Heusler alloys, NiMnSb and ${\mathrm{Co}}_{2}\mathrm{MnSi},$ attract a great deal of interest as potential spin injectors for spintronic applications. Spintronic devices require control of interfacial properties at the ferromagnet:semiconductor contact. To address this issue we report a systematic study of the ordinary and anomalous Hall effect, in ${\mathrm{Ni}}_{1.15}{\mathrm{Mn}}_{0.85}\mathrm{Sb}$ films on silicon, as a function of film thickness. In contrast to the bulk stoichiometric material, the Hall carriers in these films become increasingly electron-like as the film thickness decreases, and as the temperature increases from 50 K toward room temperature. High field Hall measurements confirm that this is representative of the majority transport carriers. This suggests that current injected from a NiMnSb:semiconductor interface may not necessarily carry the bulk spin polarization. The films also show a low temperature upturn in the resistivity, which is linked to a discontinuity in the anomalous Hall coefficient. Overall these trends indicate that the application of Heusler alloys as spin injectors will require strictly controlled interfacial engineering, which is likely to be demanding in these ternary alloys.

Effect of Low Temperature Annealing on High Field Magnetoresistance and Hall effect in (Ga, Mn)As Dilute Magnetic Semiconductors

ABSTRACTIn this paper we report the effect of low temperature annealing on the high field magnetotransport properties of epitaxial thin films of (Ga, Mn)As Dilute Magnetic Semiconductor (DMS) with low concentration (1.5 %) of Mn doping, which results in a ferromagnetic insulator. Annealing at an optimal temperature enhances the conductivity, carrier concentration, and ferromagnetic transition temperature. The field dependence of magnetoresistance is different below and above the ferromagnetic transition temperature. An attempt is made to analyze the data using a theoretical model proposed by Kaminski and Das Sarma [1].

Sign inversion of the high-field Hall slope in epitaxialLa0.5Ca0.5MnO3thin films

Magnetic and electrical properties of thin epitaxial films of the manganite ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ $(x\ensuremath{\approx}0.5)$ grown by pulsed laser deposition were investigated. The $x=0.5$ composition corresponds to a half-filled ${e}_{g}$ band and is situated on the border between ferromagnetic-metallic and antiferromagnetic-insulating behavior at low temperatures. Both different types of electrical behaviors are observed in samples with similar deposition parameters. This duality may be attributed to phase separation and the occurrence of percolating paths. The insulating ${\mathrm{La}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3}$ samples become metalliclike when magnetic fields of several tesla are applied. Hereby, resistivity drops up to six orders of magnitude occur at 50 K and 12 T. Hall effect measurements on a sample with spontaneous insulator-metal transition show a sign inversion of the high-field Hall slope around 106 K.

Magneto-Optical Spectroscopy on (Ga,Mn)As Based Layers—Correlation Between the p–d Exchange Integral and Doping

It is well established that the ferromagnetism of (Ga,Mn)As is mediated by holes. An important parameter in this context is the p–d exchange integral N0β as the RKKY interaction parameter JRKKY is proportional to (N0β)2. In magnetic semiconductors, magnitude and sign of N0β are strongly dependent on the local electronic configuration of the Mn-ion and on the free carrier density. To investigate the correlation between the p–d exchange interaction and doping in Ga1−xMnxAs, paramagnetic samples with x ≈0.1% have been intentionally n-doped with Te. High-field Hall measurements at 1.6 K confirm that with increasing degree of Te co-doping, the samples change from p- to n-type. The magnetic field induced splitting of the excitonic and electronic states has been studied by various magneto-optical spectroscopic techniques at 1.8 K and external magnetic fields up to 7.5 T. The p–d exchange integral changes from N0β > 0 (ferromagnetic coupling) to N0β < 0 (antiferromagnetic coupling) with increasing degree of Te co-doping. Thus, N0β can be tuned and can even change its sign in dependence on the doping conditions of the Mn-containing layers.

High-field magnetoresistance and Hall effect in Bi 2Sr 2CuO x crystals

In-plane magnetoresistance (MR) and Hall effect of Bi 2Sr 2CuO x crystals with T c=4– 9.5 K were investigated in DC magnetic fields up to 28 T . For T<10 K the crystals show a classical positive MR. Above 14 K , a negative MR appears. The linear T-dependence of cot Θ H in the normal state closely resembles that of the normal-state resistivity as expected for a Fermi-liquid picture.

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

We investigated the in-plane magnetoresistance and the Hall effect of high-quality Bi2Sr2CuOx 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 cotθH for the Hall angle in the normal state closely resembles that of the normal-state resistivity as expected for a Fermi liquid picture.

Large Increase in Magnetoresistance and Cluster-Glass Behavior in Defect Tl2-xMn2O7-y Pyrochlores

Moderate-pressure techniques (P = 20 kbar) have been used to prepare defect Tl{sub 2{minus}x}Mn{sub 2}O{sub 7{minus}y} pyrochlore-like materials: Neutron powder diffraction (NPD) data show that a unique stoichiometry Tl{sub 1.94}Mn{sub 2}O{sub 6.96} is stabilized under the present synthesis conditions. The defective character of these pyrochlores has a strong influence on the transport and magnetic properties. Both electrical resistance and magnetoresistance are enhanced with respect to reported data for stoichiometric Tl{sub 2}Mn{sub 2}O{sub 7}, as a consequence of the spin scattering introduced by Tl vacancies. The charge carriers are electrons, and the value obtained from the high-field Hall effect is 9.3 x 10{sup {minus}4} e{sup {minus}}/unit cell at 5 K. At the same time, a spin-glass behavior develops, subjacent to ferromagnetism, because of the weakening of the ferromagnetic (FM) interactions between near-neighbor Mn{sup 4+} cations. The observation by NPD of a distinct maximum at Q {approx} 0 suggests the existence of FM clusters near room temperature (RT), vanishing below T{sub C} to give a long-range-ordered ferromagnetic matrix.

Charge-carrier density collapse in and epitaxial thin films

We measured the temperature dependence of the linear high field Hall resistivity of La_0.67Ca_0.33MnO_3 (T_C=232K) and La_0.67Sr_0.33MnO_3 (T_C=345K) thin films in the temperature range from 4K up to 360K in magnetic fields up to 20T. At low temperatures we find a charge carrier density of 1.3 and 1.4 holes per unit cell for the Ca- and Sr-doped compound, respectively. In this temperature range electron-magnon scattering contributes to the longitudinal resistivity. At the ferromagnetic transition temperature T_C a dramatic drop in the number of current carriers $n$ down to 0.6 holes per unit cell, accompanied by an increase in unit cell volume, is observed. Corrections of the Hall data due to a non saturated magnetic state will lead a more pronounced charge carrier density collapse.

Universal behaviour of metal–insulator transitions in the p-SiGe system

Magnetoresistance measurements are presented for a strained p-SiGe quantum well sample where the density is varied through the B=0 metal–insulator transition. The close relationship between this transition, the high-field Hall insulator transition and the filling factor ν= 3 2 insulating state is demonstrated.

High field Hall effect in (DMET-TSeF) 2AuCl 2

The Hall effect of the quasi one-dimensional system (DMET-TSeF) 2AuCl 2 is reported at high fields where the system is in the FISDW (Field Induced Spin Density Wave) state. The Hall voltage shows similar but different behavior to those observed in the famous TMTSF system. The Hall voltages show step like behavior, but they are not clearly quantized. The voltage disappears above 18 T, and not the inverses of the FISDW boundary fields but the squares of them seem to show linear dependence to the phase indices n. The absolute values of the Hall voltages at the corresponding phase indices are about one tenth of the values observed in TMTSF system. Moving FISDW states have been proposed to understand the differences.

Magnetoconductivity and Hall effects in La0.67Ca0.33MnO3

The observed H2 and |H| dependence of the magnetoresistance above and below TC, respectively, may be explained by general time-reversal symmetry considerations. We further find empirically that the saturation observed in the magnetoresistance is best fit by a simple resistor in series with a magnetoconductor: ρ(H)=ρ∞+1/(σ0+γ|H|) for T&amp;lt;Tc and ρ(H)=ρ∞+1/(σ0+βH2) for T&amp;gt;TC. This provides a functional form to analyze and predict the magnetoresistance over a wide range of fields. This suggests that the underlying mechanism of ‘‘colossal magnetoresistance ’’ may be magnetoconductive, not magnetoresistive. The magnetoresistance and Hall effects on an annealed epitaxial thin films of La0.67Ca0.33MnO3 were measured at 0.9 TC and 1.1 TC. At low fields, anisotropic magnetoresistance plays a dominant role. The high field Hall effect shows holelike carriers above and below TC. The apparent change in sign at low fields is likely due to the anomalous Hall effect.

Galvanomagnetic Measurements in Acceptor doped Bi

The role of the residual resistivity ratio (RRR) measurements in the determination of the carrier concentration of tin and lead doped bismuth samples is discussed. The carrier density and the corresponding atomic pergentages of some of the samples understudy were determined by measuring the high-field Hall coefficient at 4.2K. The dependence of the transverse magnetoresistance on the magnetic field up to 2.2T is reported at low temperatures. The effect of the concentration to this behaviour is investigated.

Galvanomagnetic properties and band structure of monoclinic SrAs3.

The unusual galvanomagnetic properties of the monoclinic semimetal ${\mathrm{SrAs}}_{3}$, first-order longitudinal Hall effect and magnetoresistivity in Hall geometry, are quantitatively described within a two-band model. The ten model parameters for T\ensuremath{\rightarrow}0 K are obtained from a fit to 14 low-field coefficients in combination with high-field Hall data and Shubnikov--de Haas oscillations. The temperature variation of the galvanomagnetic coefficient can be explained most convincingly with three temperature-dependent parameters, i.e., electron and hole scattering times and electron concentration, while the anisotropy ratios are kept constant. An energy gap of 38 meV for the temperature activation of the electrons is derived from this procedure.

(De)localization of nonequilibrium electrons in Pb 1− xSn xTe(In) in high magnetic field

We report on high-field ( H<38 T) magnetoresistance and Hall effect measurements of initially dielectric Pb 0.75Sn 0.25Te(In). The data taken at 4.2 K show a magnetoresistance increase in time (localization) for a relatively low concentration of nonequilibrium electrons n. For a higher level of photoexcitation the localization disappears, and the Hall effect measurements, on the contrary, reveal an increase of n with field. The localization is attributed to energy band modulation. The delocalization is discussed in terms of field-induced electron transitions between the metastable local and extended states.

Galvanomagnetic behavior of semiconducting FeSi2 films

Hall-effect measurements in magnetic fields up to 1.5 T are performed on β-FeSi2 films between 20 and 300 K. An anomalous low-field Hall coefficient R1 in addition to the normal high-field Hall coefficient R0 is detected at temperatures below 250 K. The temperature dependence of R0 is explained by a two valence-band model and an impurity level located close to the upper valence-band edge. The temperature dependence of R1 indicates that β-FeSi2 behaves as ferromagnetic below 100 K. Correlation between the coefficient Rs=R1−R0 and the electrical resistivity ρ indicates a drastic change in magnetic ordering at about 70 K.

High-field hall effect and crystal orientation dependence of magnetoresistance in thin films of CeAl 3

Thin films of CeAl 3 on sapphire were prepared by metallic coevaporation and in vacuo annealing. Highly oriented growth with the hexagonal crystal basal plane parallel to the substrate lane was observed. The resistivity versus temperature curves of the best films were similar to bulk CeAl 3, including a T 2 dependence below 0.3 K. Transverse magnetoresistivity and Hall effect were measured in fields to 23 T and at temperatures down to 70 mK. Transverse magnetoresistivity was highly dependent on magnetic field orientation with respect to the basal plane. With the field perpendicular to the basal plane, the low-field magnetoresistivity became positive below 5 K, and the high-field magnetoresistivity exhibited a temperature-dependent maximum. With the field in the basal plane, the low-field magnetoresistivity remained negative down to 2 K, below which it exhibited a temperature-independent maximum at 1.8 T. The high-field Hall coefficient below 5 K decreased with field in a temperature-dependent manner, but was temperature-independent at all fields below 800 mK.