Giant Negative Magnetoresistance Research Articles

Influence of the electron density on the giant negative magnetoresistance in two-dimensional electron gases

variation of the electron density via a metallic gate can control the disorder potentials in two-dimensional electron gases (2DEGs). This also influences the negative magnetoresistance at low magnetic fields, which is commonly observed in ultrahigh mobility 2DEGs. We investigate the temperature-dependent giant negative magnetoresistance (GNMR) as a function of the electron density for several temperatures and currents. Thereby, we find that the GNMR behavior depends decisively on the electron density. This observation is attributed to a changed disorder potential with electron density. In the case of higher electron densities, a nonlinear current dependency of the GNMR is observed, which could be described within the hydrodynamic regime. Published by the American Physical Society 2024

Large Room-Temperature Magnetoresistance in a High-Spin Donor-Acceptor Conjugated Polymer.

Open-shell conjugated polymers (CPs) offer new opportunities for the development of emerging technologies that utilize the spin degree of freedom. Their light-element composition, weak spin-orbit coupling, synthetic modularity, high chemical stability, and solution-processability offer attributes that are unavailable from other semiconducting materials. However, developing an understanding of how electronic structure correlates with emerging transport phenomena remains central to their application. Here, the first connections between molecular, electronic, and solid-state transport in a high-spin donor-acceptor CP, poly(4-(4-(3,5-didodecylbenzylidene)-4H-cyclopenta[2,1-b:3,4-b']dithiophen-2-yl)-6,7-dimethyl-[1,2,5]-thiadiazolo[3,4-g]quinoxaline), are provided. At low temperatures (T < 180 K), a giant negative magnetoresistance (MR) is achieved in a thin-film device with a value of -98% at 10 K, which surpasses the performance of all other organic materials. The thermal depopulation of the high-spin manifold and negative MR decrease as temperature increases and at T > 180 K, the MR becomes positive with a relatively large MR of 13.5% at room temperature. Variable temperature electron paramagnetic resonance spectroscopy and magnetic susceptibility measurements demonstrate that modulation of both the sign and magnitude of the MR correlates with the electronic and spin structure of the CP. These results indicate that donor-acceptor CPs with open-shell and high-spin ground states offer new opportunities for emerging spin-based applications.

Magnetic supercapacitors: Charge storage mechanisms, magnetocapacitance, and magnetoelectric phenomena

Pseudocapacitive (PC) materials are under investigation for energy storage in supercapacitors, which exhibit exceptionally high capacitance, good cyclic stability, and high power density. The ability to combine high electrical capacitance with advanced ferrimagnetic or ferromagnetic properties in a single material at room temperature opens an avenue for the development of advanced magnetically ordered pseudocapacitive (MOPC) materials. This review covers materials science aspects, charge storage mechanisms, magnetocapacitance, and magnetoelectric (ME) phenomena in MOPC materials. Recent studies demonstrate high PC properties of advanced ferrimagnetic materials, such as spinel ferrites and hexagonal ferrites. Of particular importance is the discovery of PC properties of perovskite-type manganites, which exhibit room temperature ferromagnetism and giant negative magnetoresistance. The coupling of high capacitance and magnetization in MOPC provides a platform for strong ME interactions. Various strategies are used for manipulation of electrical capacitance/magnetization of MOPC by a magnetic field/electrode potential. Magnetocapacitance studies show significant increase in capacitance of MOPC under the influence of a magnetic field. Moreover, the application of a magnetic field results in enhanced energy density and power density, reduction of resistance, and improvement of cyclic stability. Such findings offer a potential of a breakthrough in the development of advanced supercapacitors. High magnetocapacitance and ME phenomena are linked to the influence of magnetic fields on electrolyte diffusion, structure of electrical double layer, charge transfer resistance, and variation of conductivity and magnetization of MOPC materials, which facilitate charge/discharge behavior. Various applications of ME effect in MOPC are discussed. Moreover, advantages of magnetocapacitive MOPC are described for applications in electronic and spintronic devices, supercapacitors, and devices for magnetically enhanced capacitive deionization of water.

Negative magnetoresistance in silicon doped with manganese

Based on the developed low-temperature step-by-step diffusion of impurity manganese atoms, magnetic nanoclusters of manganese atoms were formed in the crystal lattice of silicon with controllable concentration, with specified and reproducible electrophysical parameters. With the help of electron spin resonance, it was proved experimentally that magnetic nanoclusters are formed in p-Si&lt;B,Mn&gt; silicon and consist of four positively charged manganese atoms which are situated in the nearest equivalent inter-nodes around the negatively charged boron atom. Based on the study of electrophysical properties of the material obtained it is shown that in such materials an anomalous Hall effect is observed. Magnetoresistance in silicon p-Si&lt;B,Mn&gt; with magnetic nanoclusters at room temperature was studied and a giant negative magnetoresistance (NMR) Δρ/ρ~300 %, was found, it was shown that with increasing concentration of nanoclusters, NMR value essentially rate.

Perylene-based molecular device: multifunctional spintronic and spin caloritronic applications.

Carbon-based magnetic molecular junctions are promising candidates for nanoscale spintronic applications because they are atomically thin and possess high stability and peculiar magnetism. Herein, based on first-principles and non-equilibrium Green's function, we designed a carbon-based molecular spintronic device composed of carbon atomic chains, zigzag-edged graphene nanoribbon (ZGNR), and a perylene molecule. Our results show that the device exhibits integrated spintronic and spin caloritronic functionalities, such as the bias-voltage driven spin filtering effect, negative differential resistance effect and giant magnetoresistance, temperature-gradient driven spin Seebeck effect, thermal spin filtering effect, high thermal magnetoresistance, and thermal colossal giant magnetoresistance. Furthermore, considering the phonon vibration effect, the spin and charge thermoelectric figure of merits (ZTsp and ZTch) can be enhanced and the peak of ZTsp is much larger than that of ZTch, indicating the excellent thermospin performance. The asymmetrical contact configuration between the carbon atomic chain and perylene/ZGNR inhibits the phonon thermal conductivity significantly, leading to the optimal ZTsp and ZTch of 2.4 and 0.5 at 300 K, respectively. These results suggest multifunctional spintronic and spin caloritronic applications for the perylene-based molecular device.

Plateau-like magnetoresistance and topological Hall effect in Kagome magnets TbCo2 and DyCo2

Magnetoresistance (MR) and Hall resistivity of TbCo2 and DyCo2 with a Co Kagome lattice were investigated. Apart from giant negative magnetoresistance (MR) at TC, plateau-like MR and a topological Hall effect (THE) are observed at a low magnetic field for each compound below respective TC. The plateau-like MR is attributed to a compensation of negative MR with a ferromagnetically ordered structure of Tb atoms by positive MR with a noncoplanar spin structure of the Co Kagome lattice. The THE is attributed to the noncoplanar spin structure of the Co Kagome lattice only. The MR and the Hall resistivity of each compound are reduced dramatically and undergo a reversal of its sign during cooling. The reversal phenomenon at the low temperature can be related to the freezing of spins of Co atoms. The transport in DyCo2 is more sensitive to magnetic fields than that in TbCo2 which is consistent with a stronger 4f–3d interaction. Observations of these transport phenomena make RCo2 compounds promising for functional applications in spintronic devices.

In situ tunable giant electrical anisotropy in a grating gated AlGaN/GaN two-dimensional electron gas

Materials with in-plane electrical anisotropy have great potential for designing artificial synaptic devices. However, natural materials with strong intrinsic in-plane electrical anisotropy are rare. We introduce a simple strategy to produce extremely large electrical anisotropy via grating gating of a semiconductor two-dimensional electron gas (2DEG) of AlGaN/GaN. We show that periodically modulated electric potential in the 2DEG induces in-plane electrical anisotropy, which is significantly enhanced in a magnetic field, leading to an ultra large electrical anisotropy. This is induced by a giant positive magnetoresistance and a giant negative magnetoresistance under two orthogonally oriented in-plane current flows, respectively. This giant electrical anisotropy is in situ tunable by tailoring both the grating gate voltage and the magnetic field. Our semiconductor device with controllable giant electrical anisotropy will stimulate new device applications, such as multi-terminal memtransistors and bionic synapses.

Giant magnetoresistance effect in Fe-doped SrCoO2.9-δF0.1 perovskites

Excellent magnetoresistive materials have attracted people's attention due to their wide applications. Unfortunately, few cobalt-based perovskite oxides can demonstrate good magnetoresistance (MR) properties. Herein, a new series of SrCo 1-x Fe x O 2.9-δ F 0.1 (x = 0, 0.1, 0.2, and 0.3) perovskites are prepared and studied as potential magnetoresistive materials. Room temperature X-ray diffraction (XRD) and Rietveld refinement confirm the simple cubic structure of all samples. The magnetization vs temperature measurement reveals that the magnetic transition temperature goes down with the increase of Fe content, suggesting the weakened ferromagnetism caused by Fe 4+ -O-Co 3+ , Fe 3+ -O-Fe 3+ and Fe 4+ -O-Fe 4+ interactions. And the resistivity data of all Fe doped samples can be better fitted using Mott's variable range hopping (VRH) model, suggesting its disordering semi-conduction behavior. Astonishingly, the SrCo 0.8 Fe 0.2 O 2.9-δ F 0.1 ceramic sample owns the giant negative magnetoresistance value of approximately 90% at 5 K in 90 kOe, which is almost the largest negative magnetoresistance in cobalt-based perovskite oxides, indicating that cobalt-based perovskites can be an underlying material system for the research of the potential material applying to magnetic sensors or other spintronic devices.

Competition between axial anomaly and ferromagnetic ordering in Bi2-xFexSe3–xSx topological insulator: A study of magnetic and magnetotransport properties

The topological insulators Bi2-xFexSe3–xSx have been investigated by the dc-magnetization, magneto-transport and angle resolved photoemission spectroscopy (ARPES) techniques. With doping of Fe and S, a negative giant magneto-resistance (MR) is observed for parallel electric and magnetic fields (H||E). The MR behavior at lower magnetic field can be explained with the semi-classical theory whereas the MR behavior at higher field has been attributed to the axial anomaly. Interestingly, the system reached to the quantum limit at low magnetic field (∼ 4.5T). The magnetic ordering can be explained with the presence of both the RKKY (surface) and van-Vleck (bulk) interaction. The ARPES study reveals that a surface gap is suppressed when the magnetic ordering changes from ferromagnetic to anti-ferromagnetic ordering. The ARPES study and the appearance of quantum oscillations (SdH) in the resistivity pattern reveal that the topological surface property is preserved with the co-doping of Fe and S.

Superconducting fluctuations and giant negative magnetoresistance in a gate-voltage tuned two-dimensional electron system with strong spin-orbit impurity scattering

We present a quantitative theory of the gate-voltage tuned superconductor-to-insulator transition (SIT) observed experimentally in the 2D electron system created in the (111) interface between crystalline ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_{3}$ and ${\mathrm{La}\mathrm{Al}\mathrm{O}}_{3}$. Considering two fundamental opposing effects of Cooper-pair fluctuations---the critical conductivity enhancement, known as paraconductivity, and its suppression associated with the loss of unpaired electrons due to Cooper-pairs formation---we generalize the standard thermal fluctuations theory to include interaction between fluctuations within the self-consistent field approximation and quantum tunneling between mesoscopic superconducting puddles within a phenomenological approach. Relying on the quantitative agreement found between our theory and a large body of experimental sheet-resistance data, we conclude that spin-orbit scatterings, via significant enhancement of the interaction between fluctuations, strongly enhance the sheet resistance peak at high fields and reveal anomalous metallic behavior at low fields, due to mixing of relatively heavy electron bands with a light electron band near a Lifshitz point. The large enhancement of the interaction between fluctuations at high fields, where the sheet resistance is strongly amplified, is shown to result in localization of Cooper-pair fluctuations within mesoscopic puddles.

Anisotropic magnetoresistance and memory effect in bulk systems with extended defects

To describe kinetic phenomena in disordered conductors, various acts of scattering of electrons can be often considered as independent, that is captured by the Boltzmann equation. However, in some regimes, especially, in a magnetic field, it becomes necessary to take into account the correlations between different scattering events of electrons on defects at different times in the past. Such memory effects can have a profound impact on the resistivity of 2D semiconductor systems, resulting in giant negative magnetoresistance and microwave-induced resistance oscillations phenomena. This work opens the discussion of the memory effects in 3D conducting systems featured by the presence of extended one-dimensional defects, such as screw dislocations or static charge stripes. We demonstrate that accounting for the memory effect, that is the capture of electrons on collisionless spiral trajectories winding around extended defects, leads to the strong negative magnetoresistance in case when the external magnetic field direction becomes parallel to the defects axis. This effect gives rise to a significant magnetoresistance anisotropy already for an isotropic Fermi surface and no spin–orbit effects. The proposed resistivity feature can be used to detect one-dimensional scattering defects in these systems.

Relevance of weak and strong classical scattering for the giant negative magnetoresistance in two-dimensional electron gases

The giant negative magnetoresistance (GNMR), observed in two-dimensional electron gases of high mobility, is studied by controlled definition of additional short-range scatterers in form of two-dimensional Lorentz arrays of varying obstacle density, as well as in the presence of edge scattering. The results support models, which ascribe the temperature-independent regime of the GNMR to strong, classical scattering and the temperature-dependent regime to electron-electron interactions under the influence of mixed disorder. The threshold magnetic field, which separates the two regimes, is in rough agreement with the lower percolation transition of the Lorentz array. At large obstacle densities, interaction corrections are suppressed and memory effects become more relevant. Shape, amplitude, and width of the GNMR depend sensitively on the time scales of the contributing scattering mechanisms. This can lead to qualitatively similar shapes for quite different parameter values.

Giant spontaneous resistivity jumps in La0.825Ce0.175Fe12B6

We report the observation of spontaneous and very sharp resistivity jumps at low temperatures in the antiferromagnetic itinerant-electron system La0.825Ce0.175Fe12B6. This intermetallic compound undergoes multiple magnetic transformations, antiferromagnetic–ferromagnetic (AFM–FM) and ferromagnetic–paramagnetic (FM–PM), triggered by changes in both the temperature and the applied magnetic field. The magnetoresistance isotherms display irreversible abrupt steps at T ≤ 4 K, whereas the field dependence of the resistivity becomes smooth above 4 K. Meanwhile, the evolution with time of the electrical resistivity exhibits a huge spontaneous jump after an incubation time when both the applied magnetic field and temperature are constant. A giant negative magnetoresistance (MR = −71%) is discovered associated with the magnetic-field-induced first-order AFM-FM transition.

Coherent Hopping Transport and Giant Negative Magnetoresistance in Epitaxial CsSnBr3

Single-crystal inorganic halide perovskites are attracting interest for quantum device applications. Here we present low-temperature quantum magnetotransport measurements on thin film devices of epitaxial single-crystal CsSnBr$_{3}$, which exhibit two-dimensional Mott variable range hopping (VRH) and giant negative magnetoresistance. These findings are described by a model for quantum interference between different directed hopping paths and we extract the temperature-dependent hopping length of charge carriers, their localization length, and a lower bound for their phase coherence length of ~100 nm at low temperatures. These observations demonstrate that epitaxial halide perovskite devices are emerging as a material class for low-dimensional quantum coherent transport devices.

Colossal magneto-resistive relaxation effects in La0.9Ce0.1Fe12B6

The study of the magnetic, electronic transport, and magnetotransport properties of La0.9Ce0.1Fe12B6 itinerant-electron system has been performed by combining magnetization, electrical resistivity, and magnetoresistance experiments. Along with the antiferromagnetic (AFM) ordering at TN = 35 K, two consecutive magnetic transformations, antiferromagnetic–ferromagnetic (AFM–FM) and ferromagnetic–paramagnetic (FM–PM), occur upon heating under certain magnetic field values. At fixed temperatures, it is revealed that both AFM and PM phases can be converted into the FM phase irreversibly and reversibly via a first-order metamagnetic transition associated with a large hysteresis. Below 8 K, the metamagnetic transition is discontinuous, manifesting itself by multiple sudden jumps in magnetoresistance and magnetization. A giant negative magnetoresistance effect of about −78% is found. We further demonstrate that the time dependencies of the electrical resistivity and the magnetization exhibit colossal spontaneous steps after an incubation time in conditions where both the applied magnetic field and temperature are constant. Another intriguing observation in the phase diagram is the presence of a critical point at the crossover of the three distinct PM, FM, and AFM magnetic states.

Self-organized Bi-rich grain boundary precipitates for realizing steep magnetic-field-driven metamagnetic transition in Bi-doped Mn2Sb

In the present work, we reveal a novel finding, that is, self-assembled grain boundary precipitates for realizing the magnetic-field-induced metamagnetic transition by employing low melting point metal in materials. This strategy has been experimentally verified in a well-established ferrimagnetic compound Mn2Sb by doping the bismuth (Bi) element with a low melting point of just 271.3°C. Bi solidifies later than the Mn2(Sb,Bi) main phase in (Mn2Sb)1-xBix system (the melting point of ~948°C for Mn2Sb), and aggregates spontaneously along the grain boundaries, forming Bi-rich grain boundary precipitates to coat main phase grains. This is very similar to the Nd-rich grain boundary phase in Nd-Fe-B permanent magnets. The fraction of Bi-rich grain boundary phase can be controlled by Bi-content. As a result, the magnetic field induced steep magnetoelastic transition from antiferromagnetic to ferrimagnetic is achieved in (Mn2Sb)0.89Bi0.11 alloy with giant multiple functional properties in Bi-doped Mn2Sb. Especially, the magnetic entropy change maximum nearly quadruples when Bi-doping increases from 0.03 to 0.11. Giant negative magnetoresistance of more than 65% under μ0∆H = 0–5 T, and magnetostrain of ~1802 ppm under μ0H = 8.5 T are obtained in (Mn2Sb)0.89Bi0.11. It should pave a way to achieve the magnetic transition and enhance the magnetoresponsive effects in designing similar coherent materials by employing low melting point metal doping to form the dual-phase heterogeneous structure.

Electrical Transport in Polyaniline–Barium Ferrite Nanocomposites with Negative Giant Magnetoresistance

In this work, the barium ferrite/polyaniline (BaFe12O19/PANI) nanocomposites with room temperature negative giant magnetoresistance (GMR) are fabricated by the surface-initiated polymerization (SIP...

Helical Edge Transport in Millimeter-Scale Thin Films of Na3Bi.

A two-dimensional topological insulator (2DTI) has an insulating bulk and helical edges robust to nonmagnetic backscattering. While ballistic transport has been demonstrated in micron-scale 2DTIs, larger samples show significant backscattering and a nearly temperature-independent resistance of unclear origin. Spin polarization has been measured, however the degree of helicity is difficult to quantify. Here, we study 2DTI few-layer Na3Bi on insulating Al2O3. A nonlocal conductance measurement demonstrates edge conductance in the topological regime with an edge mean free path ∼100 nm. A perpendicular magnetic field suppresses spin-flip scattering in the helical edges, resulting in a giant negative magnetoresistance (GNMR) up to 80% at 0.9 T. Comparison to theory indicates >96% of scattering is helical spin scattering significantly exceeding the maximum (67%) expected for a nonhelical metal. GNMR, coupled with nonlocal measurements, thus provides an unambiguous experimental signature of helical edges that we expect to be generically useful in understanding 2DTIs.

Large negative magnetoresistance in the antiferromagnetic rare-earth dichalcogenide EuTe2

We report the synthesis and characterization of a rare-earth dichalcogenide EuTe$_2$. An antiferromagnetic transition was found at T$_M$ = 11 K. The antiferromagnetic order can be tuned by an applied magnetic field to access a first-order spin flop transition and a spin flip transition. These transitions are associated with a giant negative magnetoresistance with a value of nearly 100\%. Heat capacity measurements reveal strong electronic correlations and a reduced magnetic entropy. Furthermore, density functional theory calculations demonstrate that the electrons near the Fermi surface mainly originate from the Te 5$p$ orbitals and the magnetism is dominated by localized electrons from the Eu 4$f$ orbitals. These results suggest that both the RKKY and Kondo interactions between the local moments and itinerant electrons play crucial roles in the magnetism and large negative magnetoresistance of EuTe$_2$.

Magnetic Ordering in Systems of Identical Particles with an Arbitrary Spin

The Wigner–Eckart theorem is used for considering the collective effects related to ordering spins in systems of identical particles in ferro- and antiferromagnetic electronic systems, as well as magnetic effects that occur in high spin systems. The Hamiltonian, written in the spin representation in the form obtained by Heisenberg, Dirac, and van Vleck used to describe spin ordering in systems of particles with spin ½, is not appropriate for a description of particle systems with a spin different from ½. “High” spin particles in the spin representation need other forms of the Hamiltonian of the exchange interaction in the spin representation. The Hamiltonian for high-spin particles has been developed from the first principles, and the effects of magnetic ordering in systems of identical particles with arbitrary spin are considered in this review. An effect of giant negative magnetoresistance in the Indium antimonide has been interpreted from the exchange contribution of a high spin heavy holes point of view.