Longitudinal Magnetoresistance Measurements Research Articles

Perpendicular antiferromagnetic ordering and canted spins in van der Waals FePS3 probed by spin Hall magnetoresistance

Van der Waals antiferromagnets (AFMs) provide a two-dimensional (2D) platform for spintronic devices with exceptional properties. However, the electric transport features of the magnetic order of van der Waals AFM influenced by different field directions and amplitudes has not been demonstrated systematically. In this letter, we investigate the magnetic texture of the exfoliated van der Waals FePS3, a uniaxial AFM with perpendicular anisotropy, detected by the spin Hall magnetoresistance (SMR). Magnetic field- and temperature- dependent longitudinal magnetoresistance measurements in three orthogonal directions for the exfoliated FePS3/Pt nanostructures are conducted. The modulations in the SMR signal enable the separation of two contributions to the SMR, one of which corresponds to the negative signature of AFM SMR caused by in-plane field rotations, and the other of which is caused by canted spins in perpendicular AFM order. Our findings offer great guidance for further research and investigation using SMR approach of the magnetic texture in van der Waals AFMs.

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.

Magnetoresistance of doped silicon

We have performed longitudinal magnetoresistance measurements on heavily n-doped silicon for donor concentrations exceeding the critical value for the metal-non-metal transition. The results are compared to those from a many-body theory where the donor-electrons are assumed to reside at the bottom of the many-valley conduction band of the host. Good qualitative agreement between theory and experiment is obtained.

Experimental Evidence for Weak Insulator-Quantum Hall Transitions in GaN/AlGaN Two-Dimensional Electron Systems

We report comparative magnetoresistance measurements of the two-dimensional electron gas formed in two different GaN/AlGaN quantum well structures with different starting disorder. The longitudinal magnetoresistance measurements for both the samples exhibited temperatureindependent crossing points, evidence for a weak insulator quantum Hall transition. Our data suggest that the onset of Landau quantization does not correspond to the crossing point. Moreover, the effect of the electron-electron interaction must be taken into account because the Hall resistivity shows a strong temperature dependence in the more disordered sample. Our experimental results, therefore, urge further studies on the low-field weak insulator quantum Hall transition.

C-axis longitudinal magnetoresistance of the electron-doped superconductorPr1.85Ce0.15CuO4

We report $c$-axis resistivity and longitudinal magnetoresistance measurements of superconducting ${\mathrm{Pr}}_{1.85}{\mathrm{Ce}}_{0.15}\mathrm{Cu}{\mathrm{O}}_{4}$ single crystals. In the temperature range $13\ensuremath{\leqslant}T\ensuremath{\leqslant}32\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, a negative magnetoresistance is observed at fields just above ${H}_{C2}$. Our studies suggest that this negative magnetoresistance is caused by superconducting fluctuations. At lower temperatures $(T\ensuremath{\leqslant}13\phantom{\rule{0.3em}{0ex}}\mathrm{K})$, a different magnetoresistance behavior and a resistivity upturn are observed, whose origin is still unknown.

MR measurement of sub-micron scale relief structures fabricated in GMR materials

Understanding of magnetization process in patterned thin films is important for their applications in downsizing various magnetic devices. This paper deals with an experimental technique which enables us to characterize magnetization process in the ends of patterned ultra-thin films. In this study only the top layer of magnetic sandwich structures were patterned into an array of fine magnetic particles using electron beam lithography and Ar ion milling to form relief structures in the films. The magnetization process of the arrays was inferred from magnetoresistance (MR) measurements of the films. MR behaviors of particle array samples of substrate/FM/sub 1//Cu/FM/sub 2/ (FM/sub 1/, FM/sub 2/=Co, NiFe, CoPt) in different pattern widths of w=0.2 and 0.6 /spl mu/m, lengths L ranging from 0.2 to 280 /spl mu/m and thicknesses of t=6 and 18 nm were studied. From longitudinal MR measurements, a distinct decrease in remanent magnetization was found for sub-/spl mu/m particle arrays, which may be associated with the Formation of edge domains in the particles.

Domain nucleation processes in mesoscopic Ni80Fe20 wire junctions

The magnetization reversal process in permalloy (Ni80Fe20) wire junction structures has been investigated using magnetoresistance (MR) measurements and scanning Kerr microscopy. A combination of electron beam lithography and a lift-off process has been utilized to fabricate wires consisting of two 200 μm length regions with distinct widths w1 and w2 in the range 1–5 μm. Longitudinal MR measurements and magneto-optic Kerr effect hysteresis loops demonstrate that the magnetization reversal of the complete structure is predominantly determined by the wider region for fields applied parallel to the wire axis. Magnetic force microscopy and micromagnetic calculations show that several domain walls nucleate in the wider part and are trapped in the junction area. This implies that domain nucleation at the junction of the wire initiates magnetization reversal in the narrow half. As a consequence, the switching fields are found to be identical in both halves in this case. These results suggest the possibility of designing structures which can be used to “launch” reverse domains in narrow wires within a controlled field range.

Unusual magnetism of U 2Rh 3Si 5 in high magnetic fields

Our former investigations have shown U 2Rh 3Si 5 to exhibit at 25.5 K a spin-lattice coupled first-order transition into an antiferromagnetically ordered state. Large ordered moments of 2.3 μ B (at 9 K) align in a canted antiferromagnetic structure. In this publication we address the influence of high magnetic fields on the unusual magnetism. Specific heat measurements (<12 T), magnetization measurements (<30 T), and longitudinal magnetoresistance measurements (<20 T) on single crystalline material have been performed. The magnetic phase diagram is determined. The b -axis is the easy magnetic axis and for B>14.5 T along the b -direction the antiferromagnetic transition is suppressed. The first-order character of the magnetic ordering persists in high magnetic fields as shown by the specific heat measurements. The Fermi-surface is strongly affected by the magnetism.

High-Field Magnetization and Magnetoresistance of Single-Crystal CeRhSb

We report the high-field magnetization and longitudinal magnetoresistance measurements in magnetic fields of up to 55 T, and Hall resistivity and transverse magnetoresistance measurements in fields of up to 15 T for single crystals of CeRhSb with a pseudogap in the density of states. The magnetization at 1.3 K shows rather weak anisotropy along the orthorhombic principal axes, M a ≃ M b > M c , and the initial straight lines deviate upward near magnetic field values of 20, 30 and 25 T, respectively. The longitudinal magnetoresistance at 1.3 K is largely negative for both B // a and B // b and saturates near 30 T, while that for B // c is positive. The transverse magnetoresistance is positive and increases in proportion to B 1.5 for B // c , while those for B // a and B // b saturate at around 10 T. The Hall coefficient for B // a changes sign from positive to negative below 4 K, while that for B // c progressively increases with decreasing temperature. The Hall resistivity for B // a and B // b possesses,...

Determination of magnetic phase transitions in holmium using magnetoresistance measurements

The magnetic phase diagram of Holmium in the field–temperature plane has been determined using electrical resistance and longitudinal magnetoresistance measurements along the b-axis. Our H–T phase diagram below 70 K agrees quite well with that of Jensen and Mackintosh. We observed a splitting of the Néel temperature above approximately 1 T. This study shows that fairly simple magnetoresistance measurements can be used to establish magnetic phase diagrams of rare earth single crystals.

Magnetoresistance and energy gap of CeNiSn in high-magnetic field

The magnetization and longitudinal magnetoresistance measurements up to 36 T have been carried out on a single-crystal CeNiSn which shows metallic behavior in the resistivity along the a-axis. Large negative magnetoresistances are found along the a-, b- and c-axis in high fields above 10 T. A metamagnetic behavior in the magnetization is observed along the a-axis at around 15 T and a precursor along the b-axis at around 35 T.

Magnetoresistance of the random anisotropic Co70.4Fe4.6Si15B10 alloy

Longitudinal magnetoresistance measurements in Co70.4Fe4.6Si15B10 are reported for applied magnetic fields H varying from 0 to ±15 Oe. Two regimes were observed: one which increases with H2 and another which decreases with M2 for higher fields. The maximum in the magnetoresistance is observed for H=2.4 Oe for samples annealed for 15 min at 573 K in a transverse magnetic field of 2 kOe. The measured variation in R(H) from H=0 to 2.4 was about 0.2%. The value of H=2.4 is nearly the same field where a field-induced transition in the magnetization was observed. For samples annealed in the absence of the magnetic field the H2 term is the only one observed. The present results can be accounted for by the rotational model for uniaxial transverse anisotropy and the results are also in agreement with the random anisotropy model used to discuss the irreversibility and the field-induced transition.

Temperature dependence of longitudinal magnetoresistance in amorphous FeCrSiB alloys

Longitudinal magnetoresistance measurements on amorphous Fe 80− x Cr x B 12 Si 8 ( x = 0, 2, …, 12) alloys have been carried out in order to study the effect of chromium and external magnetic fields on these iron-based amorphous alloys. The measurements were taken in external fields up to 45 kOe in various temperatures from 4.41 to 300 K. The slope of the longitudinal magnetoresistance at 4.4 K is found to change sign from negative to positive as x increases and then tends to saturate. We have discussed various possibilities to explain this behaviour and compared our data with those from other chromium-containing amorphous alloys.

Magnetoresistance studies in the ternary spin glass (AuxCu1-x)0.99Mn0.01.

Longitudinal magnetoresistance measurements have been made on ternary spin-glass alloys ${({\mathrm{Au}}_{x}{\mathrm{Cu}}_{1\ensuremath{-}x})}_{0.99}{\mathrm{Mn}}_{0.01}$ for $0.05&lt;~x&lt;~0.60$ in the temperature range 4.2-40 K in magnetic fields up to 45 kG. The procedure adopted by us to fit the results to theory has yielded values for the $s\ensuremath{-}d$ exchange interaction constant $|J|$ and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction strength ${V}_{0}$ which are in reasonable agreement with values obtained through other studies such as magnetization measurements. Unlike earlier attempts to fit the magnetoresistance data with theory, we obtain acceptable values of $\frac{|J|}{V}$, the ratio of the exchange coupling to the Coulomb potential. The values of ${V}_{0}$ obtained are consistent with an RKKY interaction which has been damped due to a reduction in the electron mean free path.

Magnetic-flux quantization and electron localization in normal metal cylinders

We report on the magnetic flux quantization effect in hollow Mg cylinders with a radius r < 1 μm. The longitudinalmagnetoresistance measurements at fields B < 10 −2 T and temperature 1.5 < T < 10 K were analysed within the framework of two-dimensional localization theories. The observed resistance oscillations decrease with increasing diameter and temperature and are in excellent agreement with the theory of Altshuler et al.

Non-homogeneous electrical transport through silicon-on-sapphire thin films: Evidence of the internal stress influence

The non-homogeneous electrical parameters of carrier transport in silicon on sapphire (SOS) films are investigated through galvanomagnetic experiments using “MOS-Hall” thin (0.65 μm) SOS devices with low n-type dopings ( n 0 ⋍ 10 15 to 10 16 cm −3 ). Capacitance-voltage (C-V), Hall and magnetoresistance measurements are performed on the gate-controlled depleted or “active” layers of the film. Experimental results and theoretical calculations show that longitudinal magnetoresistance (LMR) measurements yield the accurate determination of anisotropy and carrier drift mobility. On the contrary, it is underlined that the (previous) characterization methods, exclusively based on C-V or Hall experiments could produce inconsistent and misleading results in SOS. This is partly due to the fact that the usual 6 valley conduction band model used for bulk silicon is no longer valid in thin SOS films, for which the high stress at Si-sapphire interface requires the adoption of a 4 valley model throughout the film; this implies a high anisotropy for carrier mobility and explains why, in SOS films, the Hall mobility is 40% lower than the drift mobility, and the LMR is higher than the transverse magnetoresistance. C-V, Hall and LMR measurements then give fully consistent results allowing one to describe the variation of the carrier scattering mechanisms across the film and to determine the exact profiles for carrier mobilities and concentration as well as for the anisotropy coefficient.

Electromagnetic properties of thin epitaxial Bi films in magnetic fields up to 85 kG

Electromagnetic measurements on thin epitaxial Bi films (thickness: 350–6350 Å) were carried out in magnetic fields up to 85 kG. The transverse magnetoresistance had a tendency of saturation with increasing magnetic fields. The tendency was stronger for thinner films. This behavior was attributed to the scattering at the grain-boundary planes parallel to the electric field. In the measurements of longitudinal magnetoresistance, the momentum value of carriers estimated from the positions of peaks or shoulders in the magnetoresistance–vs–magnetic-field curve was about 0.8×10−21 g cm/sec and agrees with the bulk Bi value. The appearance of peaks or shoulders can be interpreted by the partial diffuse scattering of carriers at film surfaces. Shubnikov–de Haas oscillations were observed in (dρ/dH) -H measurements. The oscillation period Δ (H−1) was found to depend on film thickness and the dependence was attributed to the thickness dependence of carrier densities in films. The oscillations caused by quantum size effect were not observed.

Magnetoresistance in amorphous ferromagnetic cobalt

Transverse and longitudinal magnetoresistance measurements made on thin films of amorphous cobalt yield results which are similar to those obtained for good single crystals which have the field applied along a crystallographic easy direction. This evidence is used to support the claim for the existence of a truly amorphous phase.

Longitudinal Magnetoresistance Anomalies

We have observed the anomalous longitudinal magnetoresistance conditions R(H) = 0 and 0&amp;lt;R(H) &amp;lt; R(0) on a [111]-oriented copper crystal specimen. The magnetoresistance voltages measured by two probe sets on mutually perpendicular faces of the specimen are observed to have a significant difference. Both of these effects are shown to be due to very slight misorientations of the specimen with respect to the magnetic field. In light of the observations, we present some precautions which should be observed in making longitudinal magnetoresistance measurements on high-purity materials.

ELECTRONIC TRANSITIONS IN STRONG MAGNETIC FIELDS

Various types of electron transitions in strong magnetic fields due to qualitative changes of the energy spectrum of electrons (and hence of properties of materials) were predicted and observed at certain critical values of the magnetic field. Metallic and semiconducting Bi-Sb alloys were investigated in the concentration range of Sb up to 8 at % and from 8 at % to 16 at % correspondingly. The transversal and longitudinal magnetoresistance measurements on Bi-Sb alloy single crystals were performed at various orientations of current and fields relative to the crystalline axes. The measurements were performed in magnetic fields up to 600 kOe.at temperatures from 4.2 to 77°K. The following types of electron transitions were discovered: (a) semiconductor-metal transition; (b) a transition from a semiconducting state into a state with an abnormally small energy gap between the zones referred to as a “quasimetallic”; (c) a transition semiconductor-“quasimetal”-semiconductor; (d) a transition semiconductor-“quasimetal”-semiconductor-metal; and (e) metal-semiconductor transition.