Large Negative Magnetoresistance Research Articles

Unusual metallic state in superconducting A15-type La4H23

Abstract Hydride superconductors continue to fascinate the communities of condensed matter physics and material sciences because they host the promising room-temperature superconductivity. The current research has been concentrated on the new hydride superconductors with the enhancement of the superconducting transition temperature (Tc). The multiple extreme conditions (high pressure/temperature and magnetic field) will introduce new insights on the hydride superconductors. The study of transport properties under very high magnetic fields facilitates the understanding of the superconductivity in the conventional hydride superconductors. In the present work, we report experimental evidence of an unusual metal state in a newly synthesized cubic A15-type La4H23 that exhibits superconductivity with a Tc reaching 105 K at 118 GPa. A large negative magnetoresistance is observed for strong pulsed magnetic fields in the non-superconducting state below 40 K. Moreover, we construct the full magnetic phase diagram of La4H23 up to 68 T at high pressure. The present work reveals anomalous electronic structural properties of A15-La4H23 under high magnetic fields, therefore holding great importance for advancing the understanding of quantum transport behaviors in hydride superconductors.

Unconventional room-temperature negative magnetoresistance effect in Au/n-Ge:Sb/Au devices

Non-magnetic semiconductor materials and their devices have attracted wide attention since they are usually prone to exhibit large positive magnetoresistance (MR) effect in a low static magnetic field environment at room temperature. However, how to obtain a large room-temperature negative MR effect in them remains to be studied. In this paper, by designing an Au/n-Ge:Sb/Au device with metal electrodes located on identical side, we observe an obvious room-temperature negative MR effect in a specific 50 T pulsed high magnetic field direction environment, but not in a static low magnetic field environment. Through the analysis of the experimental measurement of the Hall effect results and bipolar transport theory, we propose that this unconventional negative MR effect is mainly related to the charge accumulation on the surface of the device under the modulation of the stronger Lorentz force provided by the pulsed high magnetic field. This theoretical analytical model is further confirmed by regulating the geometry size of the device. Our work sheds light on the development of novel magnetic sensing, magnetic logic and other devices based on non-magnetic semiconductors operating in pulsed high magnetic field environment.

Large anomalous Hall effect and negative magnetoresistance in half-topological semimetals

Proposed mechanisms for large intrinsic anomalous Hall effect (AHE) in magnetic topological semimetals include diverging Berry curvatures of Weyl nodes, anticrossing nodal rings or points of non-trivial bands. Here we demonstrate that a half-topological semimetal (HTS) state near a topological critical point can provide an alternative mechanism for a large AHE via systematic studies on an antiferromagnetic (AFM) half-Heusler compound TbPdBi. We not only observe a large AHE with tanΘH ≈ 2 in its field-driven ferromagnetic (FM) phase, but also find a distinct Hall resistivity peak in its canted AFM phase. Moreover, we observe a large negative magnetoresistance with a value of ~98%. Our in-depth theoretical modelling indicates that these exotic transport properties originate from the HTS state which exhibits Berry curvature cancellation between the trivial spin-up and nontrivial spin-down bands. Our study offers alternative strategies for improved materials design for spintronics and other applications.

A peculiar topological Hall effect in noncentrosymmetric ternary carbide GdCoC2

A peculiar topological Hall effect (THE) is reported in a noncentrosymmetric ternary carbide GdCoC2. The GdCoC2 reveals a magnetic ordering transition from paramagnetic to ferromagnetic state at the Curie temperature TC = 15.6 K, followed by a commensurate-incommensurate phase transition at Tt = 14.1 K. Below Tt, the competition between an external magnetic field and magnetic interactions, including the Dzyaloshinskii–Moriya interaction, would give rise to characteristic spin textures with non-zero scalar spin chirality χijk, or even topologically protected spin configurations like skyrmions, for which the exotic spin-charge coupled phenomena are induced. Besides a large negative magnetoresistance (MR) up to ∼−52% at 14 K, a remarkably sharp topological Hall signal is observed with almost no anomalous Hall resistivity below 10 K. The topological Hall resistivity (ρxyT) of GdCoC2 reaches a maximum value of ∼0.23 μΩ cm at 3 K under μ0H = 0.6 T. The mechanism underlying the exceptional THE with relatively large ρxyT value in GdCoC2 is discussed in detail.

Formation of B2-ordered FeRh alloy thin films on annealing of pure and nitrogen doped Fe/Rh multilayers

Structural and magneto-transport properties of pure and nitrogen-doped FeRh alloy formed from thermal annealing of [Fe(36 Å)/Rh(41 Å)]20 and [FeN(36 Å)/Rh(41 Å)]20 multilayers have been studied as a function of annealing temperature (up to 750 °C). X-ray diffraction (XRD) and X-ray reflectivity (XRR) measurements are carried out to study the interdiffusion, alloy formation and phase analysis. From XRR studies, it is observed that intermixing initiates at 250 °C and the FeRh alloy phase is formed at 400 °C in both types of multilayers. Activation energy and diffusion coefficient values obtained from XRR indicate that diffusion is faster in pure Fe/Rh multilayers as compared to FeN/Rh multilayers. XRD measurements indicate the formation of the B2-ordered FeRh alloy phase at an annealing temperature (Tann) of 300 °C for pure Fe/Rh and at 400 °C for the nitrogen-doped FeN/Rh sample. PNR data at room temperature provides annealing-driven depth-dependent structures and magnetic depth-profiling at different annealing temperatures. Resistivity vs temperature (ρ-T) and magnetization (M−T) measurements shows a broad thermal hysteresis in both FeRh and nitrogen-doped FeRh alloy films. Room temperature magnetoresistance (MR) measurement shows a large negative MR of 32 % and 33 % for FeRh and nitrogen-doped FeRh alloy.

Intergranular Spin Dependent Tunneling Dominated Magnetoresistance in Helimagnetic Manganese Phosphide Thin Films.

Helical magnets are emerging as a novel class of materials for spintronics and sensor applications; however, research on their charge- and spin-transport properties in a thin film form is less explored. Herein, we report the temperature and magnetic field-dependent charge transport properties of a highly crystalline MnP nanorod thin film over a wide temperature range (2 K < T < 350 K). The MnP nanorod films of ~100 nm thickness were grown on Si substrates at 500 °C using molecular beam epitaxy. The temperature-dependent resistivity ρ(T) data exhibit a metallic behavior (dρ/dT > 0) over the entire measured temperature range. However, large negative magnetoresistance (Δρ/ρ) of up to 12% is observed below ~50 K at which the system enters a stable helical (screw) magnetic state. In this temperature regime, the Δρ(H)/ρ(0) dependence also shows a magnetic field-manipulated CONE + FAN phase coexistence. The observed magnetoresistance is dominantly governed by the intergranular spin dependent tunneling mechanism. These findings pinpoint a correlation between the transport and magnetism in this helimagnetic system.

Electrical transport mechanism and magnetoresistive behavior of trilayer La0.7Sr0.3MnO3/γ-Fe2O3/La0.7Sr0.3MnO3 (FM/FIM/FM) manganites

The magnetization, electrical transport, and magnetoresistance (MR) behavior of Pulsed Laser Deposited polycrystalline tri-layer La0.7Sr0.3MnO3 (LSMO)/γ-Fe2O3/LSMO film and single layer LSMO film on Si (100) substrates are investigated in the temperature range of 5 K–300 K. A magnetic anomaly appears in the magnetization {M(T)} and resistivity {ρ(T)} characterizations of the trilayer film at around 100 K, which is quite robust and is present even at 7 T of the applied magnetic field. The trilayer sample exhibits metal to insulator (MIT) transition at 210 K. The transport behavior of both the films is analysed in the context of nearest-neighbour small polaron hopping model (SPH), Mott variable range hopping (VRH) mechanism as well as thermal activation (TA) model in different temperature ranges for both the films under study. The correlated polarons or less mobile bipolarons exist in the metallic regime of the trilayer sample due to the presence of magnetic inhomogeneities. The low temperature resistivity upturn is observed in LSMO film, which is attributed to the spin fluctuations (Mn3+–O–Mn4+) due to thermal energy. The trilayer sample exhibits a large negative MR of (∼45%) at low temperature (5 K). It manifests consistent negative CMR effect across the whole temperature range of 5 K–210 K (MIT). The improved MR behavior of the trilayer sample as compared to the LSMO film is due to enhanced polycrystalline character of the trilayer film owing to higher grain boundary density and spin dependent scattering at both the interfaces of LSMO/γ-Fe2O3/LSMO structure.

Thermal hysteretic behavior and negative magnetoresistance in the charge density wave material EuTe4

EuTe4 is a newly-discovered van der Waals material exhibiting a novel charge-density wave (CDW) with a large thermal hysteresis in the resistivity and CDW gap. In this work, we systematically study the electronic structure and transport properties of EuTe4 using high-resolution angle-resolved photoemission spectroscopy (ARPES), magnetoresistance measurements, and scanning tunneling microscopy (STM). We observe a CDW gap of about 200 meV at low temperatures that persists up to 400 K, suggesting that the CDW transition occurs at a much higher temperature. We observe a large thermal hysteretic behavior of the ARPES intensity near the Fermi level, consistent with the resistivity measurement. The hysteresis in the resistivity measurement does not change under a magnetic field up to 7 T, excluding the thermal magnetic hysteresis mechanism. Instead, the surface topography measured with STM shows surface domains with different CDW trimerization directions, which may be important for the thermal hysteretic behavior of EuTe4. Interestingly, we observe a large negative magnetoresistance at low temperatures that can be associated with the canting of magnetically ordered Eu spins. Our work shed light on the understanding of magnetic, transport, and electronic properties of EuTe4.

Large Negative Magnetoresistance in All‐2D‐Materials‐Based Spin Valves

Two‐dimensional (2D) magnetic materials have attracted enormous interest and opened up a new direction to novel spintronic applications. Herein, a large negative magnetoresistance (MR) in all‐2D‐materials‐based vertical magnetic spin valves with nano/micro bubbles existing at the interface between the spacer layer (MoS2) and the top ferromagnetic electrode layer (Cr0.85Te or Fe3GeTe2) is demonstrated. The large negative MR, with a magnitude of ≈21.5% attained in Cr0.85Te/MoS2/Fe3GeTe2, could be fully suppressed by the elimination of the bubbles after a short argon‐protected annealing, indicating the determining role of the bubbles in modulating the spin‐related transport behavior. First‐principles calculations based on density function theory (DFT) illustrate that the compressive strain can significantly modify the spin‐resolved electronic band structures of the 2D ferromagnetic materials, and hence alter the spin polarization near the Fermi level, accounting for the negative MR phenomena with the conventional two‐current model. Herein, a new route to all‐2D‐materials‐based spintronic devices via strain engineering is provided, and also offers a new insight into the role of bubbles formed during fabricating 2D heterostructures in developing exotic properties and novel functionalities.

Dirac semimetal like transport features in high-quality Bi0.96Sb0.04 thin films

This work demonstrates that Dirac semimetal like transport properties can be observed in high quality, epitaxial Bi0.96Sb0.04 films grown by two-step growth method using molecular beam epitaxy. A large linear magnetoresistance (MR) of 825% (7 T, 1.8 K) and nonlinear Hall resistivity were observed, which indicate the presence of high mobility conducting layers that correspond to topological semimetallic layers. A field-induced semimetal-semiconductor transition appeared, which is a unique characteristic of Dirac semimetals. Large negative MR was also observed when the magnetic field was parallel to the current direction due to the chiral anomaly related to topological magnetoelectric effects. These transport phenomena are typical signatures of Dirac semimetals, which suggests that epitaxial Bi0.96Sb0.04 films can be regarded as Dirac semimetals.

Large negative magnetoresistance beyond chiral anomaly in topological insulator candidate CeCuAs&lt;sub&gt;2&lt;/sub&gt; with spin-glass-like behavior

&lt;p&gt;Large negative magnetoresistance (NMR), an important property for spintronics, requires experimental realization owing to the lack of suitable structural motifs. Herein, a remarkable NMR of up to -15% under 9 T at 2 K is demonstrated in a 112-type topological insulator candidate CeCuAs&lt;sub&gt;2&lt;/sub&gt; single crystal containing an As square net. Due to the presence of Dirac points coming from both the As square net and Ce�CCu�CAs layer in the paramagnetic state of CeCuAs&lt;sub&gt;2&lt;/sub&gt;, the possibility of chiral anomaly is examined and eliminated by investigating magnetoresistance (MR) with different magnetic field configurations and angle-dependant MR, which show no specific restriction on the configurations under the applied magnetic fields. Upon investigation of the anisotropic magnetism, a spin-glass-like behavior with &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;&lt;i&gt;f&lt;/i&gt;&lt;/sub&gt; ~ 4.5 K is observed in CeCuAs&lt;sub&gt;2&lt;/sub&gt;, indicating that the large NMR could be attributed to the spin-dependent scattering induced by the possible spin-glass state. Hall resistivity exhibits a multiband feature and hole-dominated transport properties, corresponding well with the calculated band structure. This study not only offers a new building block for large NMR but also serves as a guide for the investigating the interplay among transport properties, topology, and magnetism, and it is expected to broaden the research on spintronics.&lt;/p&gt;

Synergistic effect of lattice, electronic and magnetic modulations on the thermoelectric behaviour of Cr-substituted La0.65Bi0.20Sr0.15CoO3

A large negative magnetoresistance in LBSCCrxO can be used as an effective scheme for magnetically tuned thermoelectricity at low temperatures. The field induced increment in thermoelectric efficiency (ΔZT) is observed to be ∼500% at 50 K for Cr-25.

Ni48Ag2Mn37In13 multifunctional alloy: A room temperature inverse magnetocaloric and magnetoresistive material

An off-stoichiometric Ni-Mn-In Heusler alloy has been synthesized and studied for its magnetocaloric and magnetoresistive capabilities. Ni48Ag2Mn37In13 polycrystalline alloy has co-existing austenite and martensite phases at room temperature. On cooling the alloy from 400 K, austenite phase orders ferromagnetically at 312 K closely followed by a martensite transition around 309 K (in 0.01 T). This alloy in martensite state exhibits antiferromagnetism when the applied field is small, and as the field is increased, it attains ferromagnetic state. A metamagnetic transition is seen in isothermal magnetization near martensite transformation temperature yielding negative sloped-Arrott curves. The second order nature of the austenite-ferromagnetic transition is evidenced from local exponent (n) behavior. The entropy change is moderate around this transition and large around martensite transition which is of first order. Clausius-Clapeyron equation is used to validate the entropy change estimated from Maxwell relation. Resistivity falls acutely as the alloy transits from highly resistive martensite to highly conductive austenite phase. The magnetic field reduces the resistivity of both phases leading to a large negative magnetoresistance. Room temperature magnetocaloric effect and large magnetoresistance with low thermal and magnetic hysteresis are salient features of Ni48Ag2Mn37In13 alloy.

Investigation of exchange bias and magnetoresistance in the Si substituted Ni-Mn-In ribbon alloys

We have studied the effect of Si substituted Ni-Mn-In alloy on the exchange bias (EB) and Magnetoresistance (MR) and found that the Curie temperature of martensite phase increases with Si substitution and vanishes for × = 3 ribbon alloy. The splitting of ZFC and FC curve at low temperature confirms the exchange bias phenomenon in the ribbons. The step like behavior in the isothermal ZFC curve also confirms the exchange bias behavior. The coercive field initially increases with temperature and reaches a maximum value at 40 K, and then decreases with the increase of temperature confirms the vanishing of EB in the ribbons with the temperature. The large exchange bias field of 687 Oe is found in × = 1 ribbon at 5 K.. A large negative magnetoresistance of 22.4% is found at 260 K for × = 1 ribbon. The change in magneto resistance can be attributed to the super zone boundary nearby Fermi surface.

2D Magnetic Fe0.75Ta0.5S2: Giant Exchange Bias with Broadband Photoresponse

AbstractUnderstanding the interplay between magnetic and optoelectronic properties and developing spin‐optoelectronic devices are promising research strategies to further study 2D materials and advance their applications. Here, the broadband photoresponse in the newly synthesized magnetic Fe0.75Ta0.5S2 single crystals is reported. Because the uncompensated magnetic moment of the spin glass state is pinned by the moment of the antiferromagnetic state, a large exchange bias field of ≈1.98 T is found at 2 K when cooled down at a field of 7 T. The as‐prepared samples show a large negative magnetoresistance (nMR). The field dependence of nMRs displays a similar trend up to 50 K, which is likely to originate from the significant dependence of the localization length on magnetic field. In addition, a photodetector prepared using Fe0.75Ta0.5S2 flakes exhibits a fast response time (121.7 ms), good stability, high responsivity of 26.1 A W−1, and broadband photodetection, showing application potentials in spin‐optoelectronics.

Spin filtering effect in intrinsic 2D magnetic semiconductor Cr2Ge2Te6

All van der Waals Fe3GeTe2/Cr2Ge2Te6/graphite magnetic heterojunctions have been fabricated via mechanical exfoliation and stacking, and their magnetotransport properties are studied in detail. At low bias voltages, large negative junction magnetoresistances have been observed and are attributed to spin-conserving tunneling transport across an insulating Cr2Ge2Te6 layer. With increasing bias, a crossover to Fowler–Nordheim tunneling takes place. The negative sign of the tunneling magnetoresistance suggests that the bottom of a conduction band in Cr2Ge2Te6 belongs to minority spins, opposite to the findings of some first-principles calculations. This work shows that the vdW heterostructures based on 2D magnetic insulators are a valuable platform to gain further insight into spin polarized tunneling transport, which is the basis for pursuing high performance spintronic devices and a large variety of quantum phenomena.

Large positive and negative magnetoresistance in the magnetic EuCu4As2 crystal

In this article, we studied the magnetic and transport properties by magnetization, resistivity, and specific heat measurements for EuCu4As2 crystals with a rhombohedral structure. Strongly anisotropic magnetism and rich magnetic phases were observed under magnetic field in this compound. Interestingly, we observed two types of magnetoresistance: a large negative magnetoresistance (−55%, at 35 K, 9 T) near the magnetic transition temperature, due to reduction of magnetic scattering under magnetic field; a large positive magnetoresistance (60% at 2 K, 9 T) at lower temperatures when Eu2+ moments ordering ferromagnetically, similar to that observed in the non-magnetic isostructural analogue SrAg4As2 with possible nontrivial topological bands, which may be related to its special band structure.

Peculiarity of magnetocaloric and magnetoresistance effects in Ni–Mn–Sn–Fe alloy with successive metamagnetic structural transitions

Magnetocaloric and magnetoresistance properties originated from a metamagnetic structural transition were investigated in a Fe-doped Ni46.8Mn38.1Sn11.6Fe3.5 alloy. After annealing, the alloy exhibited the intermartensite phase that contributed to the multiple abrupt magnetization and resistivity changes during heating process of martensite transformation. As a result, three successive magnetic entropy change ΔSM peaks of 10.7, 14.5 and 9.7 J/kg·K at temperatures 275, 279 and 285 K respectively were observed, which was responsible for a wide working temperature span ΔTFWHM of 273–287 K and thus a large effective refrigeration capacity RCeff of 98.1 J/kg under 5.0 T. At the same time, a large negative magnetoresistance MR (e.g. over 26.7% at 275 K) was also revealed during heating process under 5.0 T. Such multi-functional magnetocaloric and magnetoresistance effects render Ni–Mn–Sn–Fe alloys promising working materials for magnetic refrigerants, information storage and thermal magnetoelectricity conversions.

Magnetic Properties, Magnetocaloric and Magnetoresistance Effects in Gd5In3 and Tb5In3 Compounds

The present work reports a comprehensive investigation of the structural, magnetic, and transport behaviors of the rare‐earth indium‐based intermetallics Gd5In3 and Tb5In3. The high‐temperature paramagnetic‐to‐ferromagnetic transitions in both the compounds are found to be second order, obeying a mean‐field type critical behavior. The sample shows multiple low‐temperature anomalies and clear signatures of thermal hysteresis are observed in the magnetization versus temperature data in the vicinity of such transitions. Tb5In3 shows a moderate amount of magnetocaloric effect around its high‐temperature Curie point. Interestingly, Gd5In3 shows large negative magnetoresistance at low temperatures, which is comparable to many other bulk intermetallic compounds.

Symmetry breaking in magnetoresistive devices

Detecting weak magnetic fields is paramount in areas such as scanning magnetometers and manipulation of magnetic nanoparticles, thus rendering it crucial to increase the weak-field sensitivity for developing next-generation magnetic sensors. The current approaches for high-sensitivity sensors, such as superconducting quantum interference devices, are complex and expensive. By contrast, magnetoresistive sensors and particularly extraordinary magnetoresistive sensors offer a simple operation at room temperature but, to date, at inferior sensitivity. To overcome these challenges, we induce device symmetry breaking to enhance the weak magnetic field sensitivity in semiconductor-metal hybrid structures exhibiting extraordinary magnetoresistance. Retaining the device mirror symmetry yields symmetric magnetoresistance curves with $R(B)=R(\ensuremath{-}B)$, which results in inferior detection of weak magnetic fields as ${[dR/dB]}_{B\ensuremath{\rightarrow}0}=0$. Using finite element modeling, we study the change in device behavior as the symmetry is broken by varying the device geometry by spatially varying the constituent material properties or both. We show that symmetry breaking has three important implications: First, breaking the mirror symmetry causes an asymmetric sensor response with $R(B)\ensuremath{\ne}R(\ensuremath{-}B)$, benefiting from a largely enhanced sensitivity to weak magnetic fields and detection of the magnetic field direction. Second, an interplay with the Hall effect causes a large negative magnetoresistance exceeding 79% at $B=1$ T and room temperature without magnetic constituents or explicit optimization of this property. Third, the asymmetric geometries can be used as a key ingredient toward designing on-demand magnetoresistive characteristics such as linearity at low magnetic fields, step functions, and magnetic switchlike behavior. These implications pave the way for asymmetric topology optimization of magnetoresistive devices with unparalleled performance.