Magnetoresistance Changes Research Articles

Unraveling magneto-elastoresistance in the Dirac nodal-line semi-metal ZrSiSe

Quantum materials are often characterized by a marked sensitivity to minute changes in their physical environment, a property that can lead to new functionalities and thereby, to novel applications. One such key property is the magneto-elastoresistance (MER), the change in magnetoresistance (MR) of a metal induced by uniaxial strain. Understanding and modeling this response can prove challenging, particularly in systems with complex Fermi surfaces. Here, we present a thorough analysis of the MER in the nearly compensated Dirac nodal-line semi-metal ZrSiSe. Small amounts of strain (0.27%) lead to large changes (7%) in the MR. Subsequent analysis reveals that the MER response is driven primarily by a change in transport mobility that varies linearly with the applied strain. This study showcases how the effect of strain tuning on the electrical properties can be both qualitatively and quantitatively understood. A complementary Shubnikov-de Haas oscillation study sheds light on the root of this change in quantum mobility. Moreover, we unambiguously show that the Fermi surface consists of distinct electron and hole pockets revealed in quantum oscillation measurements originating from magnetic breakdown.

Quantum Transport through a Quantum Dot Coupled to Majorana Nanowire and Two Ferromagnets with Noncollinear Magnetizations.

We study the electron tunneling (ET) and local Andreev reflection (AR) processes in a quantum dot (QD) coupled to the left and right ferromagnetic leads with noncollinear ferromagnetisms. In particular, we consider that the QD is also side-coupled to a nanowire hosting Majorana bound states (MBSs) at its ends. Our results show that when one mode of the MBSs is coupled simultaneously to both spin-up and spin-down electrons on the QD, the height of the central peak is different from that if the MBS is coupled to only one spin component electrons. The ET and AR conductances, which are mediated by the dot-MBS hybridization, strongly depend on the angle between the left and right magnetic moments in the leads. Interaction between the QD and the MBSs will result in sign change of the angle-dependent tunnel magnetoresistance. This is very different from the case when the QD is coupled to regular fermonic mode, and can be used for detecting the existence of MBSs, a current challenge in condensed matter physics under extensive investigations.

Peculiarities of magnetoresistance in GaAs whiskers at low temperatures

Magnetoresistance of GaAs whiskers with concentrations in the vicinity to metal-insulator transition (MIT) 1017–1018 cm−3 were studied at low temperatures and high magnetic fields (up to 14 T). The whiskers were doped with Te during the growth. The whisker diameter ranges from 10 to 40 μm. Temperature dependence of the whisker resistance have shown metallic and semiconductor character in the proximity to MIT from various sides of the transition. Depending on doping level the character of the whisker magnetoresistance changes from linear positive to quadratic negative. The magnetoresistance of metallic whiskers is explained in terms of weak antilocalization (WAL) model. The specimens with semiconductor character of conductance revealed negative magnetoresistance, magnitude of which rises due to moving away from MIT and reach 15% for the whiskers with concentration 1017 cm−3. The possible reasons of the negative magnetoresistance are discussed. The effect observed is attributed to weak localization (WL) of charge carriers in the region of hopping conductance for the whiskers in the vicinity to MIT. A high negative magnetoresistance (NMR) for the whiskers of low dopant concentration is connected with subsurface conductance in the disordered upper layers of the whiskers due to their core-shell structure.

Theory of electron spin resonance in scanning tunneling microscopy

Electron spin resonance (ESR) spectroscopy in scanning tunneling microscopy (STM) has enabled probing the electronic structure of single magnetic atoms and molecules on surfaces with unprecedented energy resolution, as well as demonstrating coherent manipulation of single spins. Despite this remarkable success, the field could still be greatly advanced by a more quantitative understanding of the ESR-STM physical mechanisms. Here, we present a theory of ESR-STM that quantitatively models not only the ESR signal itself, but also the full background tunneling current, from which the ESR signal is derived. Our theory is based on a combination of Green's function techniques to describe the electron tunneling and a quantum master equation for the dynamics of the spin system along with microwave radiation interacting with both the tunneling current and the magnetic system. We show that this theory is able to quantitatively reproduce the experimental results for a spin-1/2 system (TiH molecules on MgO) across many orders of magnitude in tunneling current, providing access to the relaxation and decoherence rates that govern the spin dynamics due to intrinsic mechanisms and to the applied bias voltage. More importantly, our work establishes that (i) sizable ESR signals, which are a measure of microwave-induced changes in the junction magnetoresistance, require surprisingly high tip spin polarizations, and (ii) the coupling of the magnetization dynamics to the microwave field gives rise to the asymmetric ESR spectra often observed in this spectroscopy. Additionally, our theory provides very specific predictions for the dependence of the relaxation and decoherence times on the bias voltage and the tip-sample distance. Finally, with the help of electromagnetic simulations, we find that the transitions in our ESR-STM experiments, in which the tunnel junction is irradiated by a nearby microwave antenna, can be driven by the ac magnetic field at the junction. Published by the American Physical Society 2024

Unconventional magnetotransport properties of two-dimensional ferromagnet Fe5GeTe2

Two-dimensional (2D) van der Waals FexGeTe2 metallic ferromagnets have Curie temperature near or even higher than room temperature, showing great prospects in the field of spintronics. Here, we study the magnetotransport properties of Fe5GeTe2 nanoflakes. Multiple sign changes of angle-dependent magnetoresistance (ADMR) are observed with changing temperature or magnetic field. The high field-induced negative to positive MR transition in low temperatures (T < 50 K) and the temperature-induced sign reversal of anisotropic MR at T = 130 K are responsible for these exotic and complex characteristics of ADMR. In addition, the electron–magnon scattering induced negative MR exhibits abnormal nonmonotonic temperature dependence, which is related to the nonmonotonic variation of anomalous Hall resistance and the transition of the carrier types at T = 150 K. The exotic magnetotransport properties of Fe5GeTe2 revealed in this work may help pave the way for the practical application of this 2D magnetic material.

Solar-Powered Switch of Antiferromagnetism/Ferromagnetism in Flexible Spintronics.

The flexible electronics have application prospects in many fields, including as wearable devices and in structural detection. Spintronics possess the merits of a fast response and high integration density, opening up possibilities for various applications. However, the integration of miniaturization on flexible substrates is impeded inevitably due to the high Joule heat from high current density (1012 A/m2). In this study, a prototype flexible spintronic with device antiferromagnetic/ferromagnetic heterojunctions is proposed. The interlayer coupling strength can be obviously altered by sunlight soaking via direct photo-induced electron doping. With the assistance of a small magnetic field (±125 Oe), the almost 180° flip of magnetization is realized. Furthermore, the magnetoresistance changes (15~29%) of flexible spintronics on fingers receiving light illumination are achieved successfully, exhibiting the wearable application potential. Our findings develop flexible spintronic sensors, expanding the vision for the novel generation of photovoltaic/spintronic devices.

Modulation of spin Hall magnetoresistance in α-Fe2O3/Pt by uniaxial tensile strain

We demonstrate the modulation of spin Hall magnetoresistance (SMR) by uniaxial tensile strain at RT in heterostructures of antiferromagnetic insulating (0001)-oriented α-Fe2O3 (hematite) and Pt. The SMR signals consistent with previous reports are observed in α-Fe2O3/Pt without strain. Under tensile strains, we found that the magnetoresistance amplitude changes almost linearly with the strain amplitude. The observed magnetoresistance change is attributed to the strain modulation of SMR owing to the change in domain distribution via magnetoelastic couplings. The results provide a useful method for controlling the spin-dependent transport effect in antiferromagnetic-insulator/metal bilayers.

3D Printable Self‐Sensing Magnetorheological Elastomer

AbstractMagnetorheological elastomers (MREs) are a category of smart materials composed of a magnetic powder dispersed in an elastomeric matrix. They are characterized by the ability to change their mechanical properties when an external magnetic field is applied, called magnetorheological (MR) effect. When a conductive filler is added to a magnetorheological elastomer, the resulting hybrid filler composite showcases both MR and piezoresistive effects. For such a reason, these composites are referred to as self‐sensing magnetorheological elastomers. In this case, the synthesized self‐sensing magnetorheological elastomers are based on styrene‐based thermoplastic elastomers (TPS), carbonyl iron particles (CIP), and carbon black (CB). The hybrid filler concept using various coated CIP and constant CB content showed that above 25 vol.% CIP the resistivity increased rapidly. This work proposes the first case of a 3D printable self‐sensing magnetorheological elastomer and cyclic mechanical compression and tensile mode analysis at high deformation (up to 20% and 10%, respectively). The results showcase a magnetoresistive change of up to 68% and a piezoresistive change of up to 42% and 98% in compression and tension, respectively. In addition, the magnetostriction of the self‐sensing samples has been characterized to be 3.6% and 5.6% in the case of CIP 15 and 30 vol.%, respectively.

Evolution of the domain structure in a FeNiCo nanowire under the action of a magnetic field

Based on the experimentally discovered domain structure and its evolution in an external magnetic field in thin films of FeNiCo composition with uniaxial anisotropy, a theoretical model of the magnetization distribution is proposed. The analytical dependence of the domain size on the magnitude of the magnetic field is obtained. The change in magnetoresistance because of the evolution of the magnetic domain structure is calculated.

Investigating magnetoresistance properties on a periodic poly(dA)-poly(dT) DNA structure

Magnetoresistance has been calculated for a range of magnetic fields. The calculation has been carried out using a periodic DNA structure. The magnetic field affects electron hopping constants in a tight-binding Hamiltonian regime through the Peierls phase. On the other hand, the internal electric field, as a result of the voltage difference across the molecule structure, affects the magnitude of electron hopping parameters. Green’s function method has been employed in computing the electron transmission probabilities. Then, the Landauer-Buttiker formula is used in computing currents at a certain voltage. The magnetoresistance was observed oscillating as the magnetic field increased, just like the current. At several voltages, the magnetoresistance changes sign with the change in the magnetic field.

Single-shot switching in Tb/Co-multilayer based nanoscale magnetic tunnel junctions

Magnetic tunnel junctions (MTJs) are elementary units of magnetic memory devices. For high-speed and low-power data storage and processing applications, fast reversal of the magnetization by an ultrashort laser pulse is extremely important. We demonstrate single-shot switching of Tb/Co-multilayer based nanoscale MTJs by combining the optical writing and the electrical read-out methods. A 90-fs-long laser pulse switches the magnetization of the storage layer (SL). The change in the tunneling magnetoresistance (TMR) between the SL and a reference layer (RL) is probed electrically across the oxide barrier. Single-shot switching is demonstrated by varying the cell diameter from 300 nm to 20 nm. The anisotropy, magnetostatic coupling, and switching probability exhibit cell-size dependence. By suitable association of laser fluence and magnetic field, successive commutation between high-resistance and low-resistance states is achieved. The nature of the magnetization reversal of both SL and RL in a continuous film is probed with a depth-resolved magneto-optical Kerr effect (MOKE) magnetometry. The ultrafast dynamics in the continuous full-MTJ stack is investigated with the time-resolved pump–probe technique. Our experimental findings provide strong support for the growing interest in ultrafast spintronic devices.

Abnormal sign change of angle-dependent magnetoresistance in polycrystalline WTe2 nanoplate

Abnormal sign change of angle-dependent magnetoresistance in polycrystalline WTe2 nanoplate

Electrical transport under extreme conditions in the spin-ladder antiferromagnetTaFe1.25Te3

We report the electrical transport of the layered, spin-ladder antiferromagnet ${\mathrm{TaFe}}_{1.25}{\mathrm{Te}}_{3}$ (${T}_{N}\ensuremath{\sim}167$ K) under intense magnetic field (up to 60 T) and high pressure (up to 50 GPa). In high magnetic field, ${\mathrm{TaFe}}_{1.25}{\mathrm{Te}}_{3}$ undergoes two metamagnetic transitions, manifested in both the magnetoresistance and the Hall resistivity. Synchrotron x-ray diffraction reveals no obvious structural transition up to $\ensuremath{\sim}50$ GPa. However, the application of a small pressure ($\ensuremath{\sim}0.7$ GPa) fosters a sizable anomalous Hall conductivity and a negative magnetoresistance, possibly arising from the competing ferromagnetic exchange interaction in this antiferromagnet. Both the anomalous Hall conductivity and the negative magnetoresistance culminate at a pressure of $\ensuremath{\sim}4$ GPa. With further increase of pressure, both physical quantities diminish. The Hall coefficient and the magnetoresistance change sign above $\ensuremath{\sim}20$ GPa, presumably due to the cessation of ferromagnetic spin fluctuations in this high pressure regime.

Electric transport properties of Cu-doped NbTe2 single crystals

NbTe2 is a monoclinic quasi-two-dimensional layered semimetal. This paper reports the change of physical properties of NbTe2 single crystals under the action of copper substitution. The zero-field ab-plane resistivity ρxx shows that the samples havegood metallicity. Magnetoresistance changes of up to 23% were observed at a magnetic field of 13 T without any tendency to saturate. We have observed linear magnetoresistance under high magnetic field, which will be attributed to the linear band dispersion of small Fermi pockets. And we use a formula to describe the linear relationship: ρ=NiBπn2ec∝B. The curve of the Hall resistance changing with the magnetic field at the same temperature has a linear relationship with the magnetic field, and the slope is positive, which indicates that the carrier type is mainly hole-type carriers.

Persistent modification of magnetotransport properties in LaAlO3/SrTiO3 by gate-induced modification of structural domains

We investigate the influence of large electric fields on the transport properties of nanostructures patterned into the electron gas at the interface between ${\mathrm{LaAlO}}_{3}$ and ${\mathrm{SrTiO}}_{3}$ (100). In these nanostructures, the transport is largely dominated by domain walls between structural domains in the ${\mathrm{SrTiO}}_{3}$ appearing below a structural phase transition temperature. We find that both positive and negative gate voltages applied in a side-gate configuration can induce persistent changes in the sample that are only reversed by warming through the phase transition. These changes include a resistance increase and a change in magnetoresistance in magnitude and sign. Furthermore, a resistance anomaly during warm-up that has been observed in the past can be further increased by briefly applying a side-gate voltage. These effects are typically observed in nanostructures below a certain size limit. The electric fields also increase this size limit from a few-hundred nm to more than 1 $\ensuremath{\mu}\mathrm{m}$. All these observations can be consistently explained by a field-induced removal of specific domain-wall types accompanied by an increasing domain size and a reduced number of domain walls in the structures. The results not only show that under certain conditions domain walls can dominate the transport properties even of micron-sized structures, but they also provide an additional tuning knob to induce nonvolatile changes in the transport properties of ${\mathrm{LaAlO}}_{3}\text{/}{\mathrm{SrTiO}}_{3}$ interfaces at low temperatures.

Tunable Perpendicular Magnetoresistive Sensor Driven by Shape and Substrate Induced Magnetic Anisotropy

AbstractControl of magnetization reversal processes is a key issue for the implementation of magnetic materials in technological applications. The modulation of shape magnetic anisotropy in nanowire structures with a high aspect ratio is an efficient way to tune sharp in‐plane magnetic switching. However, control of fast magnetization reversal processes induced by perpendicular magnetic fields is much more challenging. Here, tunable sharp magnetoresistance changes, triggered by out‐of‐plane magnetic fields, are demonstrated in thin permalloy strips grown on LaAlO3 single crystal substrates. Micromagnetic simulations are used to evaluate the resistance changes of the strips at different applied field values and directions and correlate them with the magnetic domain distribution. The experimentally observed sharp magnetic switching, tailored by the shape anisotropy of the strips, is properly accounted for by numerical simulations when considering a substrate‐induced uniaxial magnetic anisotropy. These results are promising for the design of magnetic sensors and other advanced magnetoresistive devices working with perpendicular magnetic fields by using simple structures.

High-dose X-ray radiation induced MgO degradation and breakdown in spin transfer torque magnetic tunnel junctions

Magnetic tunnel junction (MTJ) with magnesium oxide (MgO) tunnel barrier is the core element of spin transfer torque-based magnetic random access memory. For the application in the space environment, the total ionizing dose radiation effects on MTJs need to be evaluated. In this work, the MTJs were exposed to X-ray radiation with different doses of up to 10 Mrad(Si). Measurements of current induced magnetization switching (CIMS) behavior of these MTJs were performed before and after radiation. The results show negligible changes in the tunneling magnetoresistance and current switching properties after 8 Mrad(Si) X-ray radiation. However, with a total dose of 9 Mrad(Si), a significant reduction in junction resistance of a fairly large number of MTJs was observed, which showed characteristics of MTJ breakdown. Moreover, in this study, all experimental MTJs became functionally disabled due to MgO breakdown under 10 Mrad(Si) X-ray radiation. The CoFeB/MgO/CoFeB interface microstructure was observed using X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy (HRTEM). Interfacial structural results indicate that the MgO degradation and breakdown behavior caused by X-ray ionizing radiation can give rise to radiation-induced oxygen vacancies across the tunnel barrier oxide layer.

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.

Large magnetocaloric and magnetoresistance effects during martensitic transformation in Heusler-type Ni44Co6Mn37In13 alloy

NiMn-based Heusler alloys are promising materials in the multi-functional applications due to their ample magneto-responsive effects across martensitic transformation, such as magnetocaloric effect, magnetostriction and magnetoresistance. In this work, the evolution of microstructure, large magnetocaloric and magnetoresistance effects during martensitic transformation are systematically studied in a Ni44Co6Mn37In13 alloy. Magnetic and caloric measurements verify that the martensite in weak magnetic state would gradually transform to be ferromagnetic austenite upon heating. The temperature dependence of microstructure observed in an in-situ optical microscopy unambiguously verify the ‘kinetic arrest’ of martensitic transformation. Most importantly, due to the high sensitivity of transformation to the magnetic field, large magnetocaloric and magnetoresistance effects near room temperature are obtained, including magnetic entropy changes of 8.4 Jkg-1K−1, effective refrigerant capacity of 181 Jkg−1 and magnetoresistance change of 75 % under the field change of Δμ0H = 0–5 T, making the studied sample promising for room temperature magnetic refrigeration and magnetic storage.

Unusual Magnetotransport from two-dimensional Dirac Fermions in Pd3Bi2Se2

Pd$_{3}$Bi$_{2}$Se$_{2}$ has been proposed to be topologically non-trivial in nature. However, evidence of its non-trivial behavior is still unexplored. We report the growth and magneto-transport study of Pd$_{3}$Bi$_{2}$Se$_{2}$ thin films, revealing for the first time the contribution of two-dimensional (2D) topological surface states. We observe exceptional non-saturated linear magnetoresistance which results from Dirac fermions inhabiting the lowest Landau level in the quantum limit. The transverse magnetoresistance changes from a semi-classical weak-field $B^{2}$ dependence to a high-field $B$ dependence at a critical field $B^{\star}$. It is found that $B^{\star} \propto T^2$, which is expected from the Landau level splitting of a linear energy dispersion. In addition, the magnetoconductivity shows signatures of 2D weak anti-localization (WAL). These novel magnetotransport signatures evince the presence of 2D Dirac fermions in Pd$_{3}$Bi$_{2}$Se$_{2}$ thin films.