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Simplified illustration of the current flow in a typical system in both low and high applied magnetic fields
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We show that extraordinary magnetoresistance (EMR) arises in systems consisting of two components; a semiconducting ring with a metallic inclusion embedded. The important aspect of this discovery is that the system must have a quasi-two-dimensional character. Using the same materials and geometries for the samples as in experiments by Solin et al.1...
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... flows through the conducting Au inclusion giving a low resistance path. However, the application of a large mag- netic field forces the current to flow around the perimeter of the disk avoiding the conducting inclusion, as if there was a ring of semiconductor with a cavity in the centre, thus creating a significantly higher resistance path, see Fig. ...
Citations
... The concentric circular and bar-shaped devices are the most commonly studied geometries and here a magnetoresistance up to 1.5 · 10 6 % for InSb and 1 · 10 7 % for encapsulated graphene have been shown experimentally at B = 5 T [8,30]. The devices are generally symmetric, leading to an overall symmetric magnetoresistance where R(B) ≈ R(−B), yielding a sensitivity of dR/dB − → 0 for B − → 0 T. In these devices, several studies report the effect of changing geometric parameters such as the semiconductor width and the area of the metal region [8,18,33,35,38,42,43]. The device symmetry is broken in the off-centered geometry, where simulations predict highly asymmetric magnetoresistance curves and a non-zero sensitivity (dR/dB > 0) towards weak magnetic fields [41]. ...
Extraordinary magnetoresistance (EMR) is a geometric magnetoresistance emerging in hybrid systems typically comprising a high-mobility material and a metal. Due to a field-dependent redistribution of electrical currents in these devices, the electrical resistance at room temperature can increase by 10^7% when applying a magnetic field of 5 T. Although EMR holds considerable potential for realizing sensitive, all-electronic magnetometers, this potential is largely unmet. A key challenge is that the performance of EMR devices depends very sensitively on variations in a vast parameter space where changes in the device geometry and material properties produce widely different EMR performances. The challenge of navigating in the large parameter space is further amplified by the poor understanding of the interplay between the device geometry and material properties. By systematically varying the material parameters in four key EMR geometries using diffusive transport simulations, we here elucidate this interplay with the aim of finding universal guidelines for designing EMR devices. Common to all geometries, we find that the sensitivity scales inversely with the carrier density, while the MR reaches saturation at low carrier densities. Increasing the mobility beyond 20,000 cm^2/Vs is required to observe strong EMR effects at 1 T with the optimal magnetoresistance observed for mobilities between 100,000-500,000 cm^2/Vs. An interface resistance below 10^-4 Ohm*cm^2 between the constituent materials in the hybrid devices was also found to be a prerequisite for very high magnetoresistances in all geometries. By further simulating several high-mobility materials at room and cryogenic temperatures, we conclude that encapsulated graphene and InSb are amongst the most promising candidates for EMR devices showing high magnetoresistance exceeding 10^7% below 1 T at room temperature. This study paves the way for understanding how to realize EMR devices with record-high magnetoresistance and high sensitivity for detecting magnetic fields.
... The effect of varying the filling factor defined as the ratio of the radii of the shunt and the outer boundary, = ⁄ , have been demonstrated in both experiments 1,6,7,9,24,27,43,45 and simulations. 5,32,58,59,63,64 The experimental results and simulations have both shown that increasing α decreases the overall resistance, but improves the magnetoresistance as the R(0) term decreases faster than R(B). This improvement continues up to a threshold value of α, after which the magnetoresistance for a fixed magnetic field drops as the current cannot effectively be deflected around the shunt (see Figure 2.4). ...
Extraordinary magnetoresistance (EMR) is a geometric magnetoresistance effect occurring in hybrid devices consisting of a high-mobility material joined by a metal. The change in resistance can exceed 107% at room temperature when a magnetic field of 5 T is applied. Magnetic field sensors based on EMR hold the potential formeasuring weak magnetic fields with an unprecedented sensitivity, yet, to date this potential is largely unmet. In this work, we provide an extensive review of the current state-of-the-art in EMR sensors with a focus on the hybrid device geometries, the constituent material properties and applications of EMR. We present a direct comparison of the best devices in literature across magnetoresistance, sensitivity and noise equivalent field for different materials and geometric designs. The compilation of studies collected in this review illustrates the extremely rich possibilities for tuning the magnetoresistive behavior varying the device geometry and material properties. In addition, we aim to improve the understanding of the EMR effect and its interplay with geometry and material properties. Finally, we discuss recent trends in the field and future perspectives for EMR.
... The filling factor and geometry dependence besides having been studied in several other investigations [116,126,127]. A random branch and droplet model (RBDM) [128] was applied to a vdP disk geometry. The relevance of this study result lies in its capability to be employed to EMR field detectors using more popular semiconducting substances like silicon. ...
Magnetic sensing devices are of the extremely significant kind of detectors, that are used several important and useful applications. Geometrical extraordinary magnetoresistance (EMR) is the geometrical kind of magnetoresistance associated with the non-magnetic semiconductor-metal hybrid structure and influenced by geometrical shape. As a result of Lorentz force, the current path change from metal (in absence of magnetic field) to semiconductor (under the subjection of the magnetic field) in semiconductor-metal hybrid structure is the key of EMR phenomena, i.e. once the metal is placed in a semiconductor, it works as a short circuit with the majority of applied current moving through metallic inhomogeneity and the almost whole resistance of semiconductor-metal hybrid structure drops to value smaller than that of homogeneous semiconductor in absence of magnetic field, in other hands, applying of magnetic field alters the current route to be around the metallic inhomogeneity where it works as an open circuit and the whole resistance turns into a quite high magnitude relies on the geometrical form of a device. The variables govern these phenomena are metal and semiconductor conductivity, semiconductor charge carriers mobility, and device geometry. Within this review, EMR phenomena history, variables governed it, materials, and applications of EMR devices are overviewed.
... Refinements to the original devices enable detectors suitable for fine-scale magnetic field sensors 2,6,7 . EMR can be enhanced by tailoring the shape of the shunt and also by asymmetries in the overall device configuration [8][9][10] . ...
We report a proof-of-concept study of extraordinary magnetoresistance (EMR) in devices of monolayer graphene encapsulated in hexagonal boron nitride, having metallic edge contacts and a central metal shunt. Extremely large EMR values, $MR=(R(B) - R_0) / R_0\sim 10^5$, are achieved in part because $R_0$ approaches or crosses zero as a function of the gate voltage, exceeding that achieved in high mobility bulk semiconductor devices. We highlight the sensitivity, $dR/dB$, which in two-terminal measurements is the highest yet reported for EMR devices, and in particular exceeds prior results in graphene-based devices by a factor of 20. An asymmetry in the zero-field transport is traced to the presence of $pn$-junctions at the graphene-metal shunt interface.
... A quadratic MR dependence on magnetic flux density B was observed by several authors as usual behavior for semiconductor materials at low magnetic fields [32][33][34] . However, creating inhomogeneities or with applied nanoscale manipulation (functionalization of graphene, combination of graphene with different type of substrate materials like boron nitride, black phosphorus, and etc.) it is possible to induce a large non-saturating linear magnetoresistance, desirable property for practical applications 32 . ...
The demand to increase the sensitivity to magnetic field in a broad magnetic field ranges has led to the research of novel materials for sensor applications. Therefore, the hybrid system consisting of two different magnetoresistive materials – nanostructured Co-doped manganite La1−xSrx(Mn1−yCoy)zO3 and single- and few-layer graphene – were combined and investigated as potential system for magnetic field sensing. The negative colossal magnetoresistance (CMR) of manganite-cobaltite and positive one of graphene gives the possibility to increase the sensitivity to magnetic field of the hybrid sensor. The performed magnetoresistance (MR) measurements of individual few layer (n = 1–5) graphene structures revealed the highest MR values for three-layer graphene (3LG), whereas additional Co-doping increased the MR values of nanostructured manganite films. The connection of 3LG graphene and Co-doped magnanite film in a voltage divider configuration significantly increased the sensitivity of the hybrid sensor at low and intermediate magnetic fields (1–2 T): 70 mV/VT of hybrid sensor in comparison with 56 mV/VT for 3LG and 12 mV/VT for Co-doped magnanite film, respectively, and broadened the magnetic field operation range (0.1–20) T of the produced sensor prototype.
... In this regime, the formation of Li 4 Ti 5 O 12 phase may lead to more boundaries in phase separated samples. Such inhomogeneity in the magnetic field usually exhibits strong p-MR 34,35 . For the samples S1-S5, the p-MR below T ch mainly origins from the orbital-related state since the LiTi 2 O 4-δ phase dominates the transport 25 . ...
The evolution from superconducting LiTi2O4-δto insulating Li4Ti5O12thin films has been studied by precisely tuning the oxygen pressure in the sample fabrication process. In superconducting LiTi2O4-δfilms, with the increase of oxygen pressure, the oxygen vacancies are filled gradually and the c-axis lattice constant decreases. When the oxygen pressure increases to a certain critical value, the c-axis lattice constant becomes stable, which implies that the sample has been completely converted to Li4Ti5O12phase. The two processes can be manifested by the angular bright-field images of the scanning transmission electron microscopy techniques. The transition temperature (Tch) of magnetoresistance from the positive to the negative shows a nonmonotonic behavior, i.e. first decrease and then increase, with the increase of oxygen pressure. We suggest that the decrease Tchcan be attributed to the suppressing of orbital-related state, and the inhomogeneous phase separated regions contribute positive MR and thereby lead to the reverse relation between Tchand oxygen pressure.
... On the other hand, hybrid nanostructures of plain materials exhibit mainly intriguing MR versions, such as giant MR observed in ferromagnet/normal-metal/ferromagnet trilayers 5,6 and tunnel MR observed in ferromagnet/ insulator/ferromagnet ones 7,8 , when subjected to a parallel external magnetic field. Even stronger MR effects have been reported, the so-called extraordinary MR is recorded in normal-metal/semiconductor hybrid structures 9,10 , and the so-called extremely large MR is observed in layered transition-metal dichalcogenide compounds 11 . Some of these MR effects have already promoted the realization of devices that operate effectively in room-temperature and/or cryogenic-environment conditions. ...
... Specifically, FM/SC/FM TLs exhibit SMR when they are driven to the coercive field, H C by a parallel H ex 15,16 . The out-of-plane magnetic domains (MDs) and MDs walls (MDWs) that develop at H C are accompanied by transverse stray dipolar fields that magnetostatically couple the FM outer layers through the SC Scientific RepoRts | 5:13420 | DOi: 10.1038/srep13420 interlayer 12,13,24 . ...
Magnetoresistance is a multifaceted effect reflecting the diverse transport mechanisms exhibited by different kinds of plain materials and hybrid nanostructures; among other, giant, colossal, and extraordinary magnetoresistance versions exist, with the notation indicative of the intensity. Here we report on the superconducting magnetoresistance observed in ferromagnet/superconductor/ferromagnet trilayers, namely Co/Nb/Co trilayers, subjected to a parallel external magnetic field equal to the coercive field. By manipulating the transverse stray dipolar fields that originate from the out-of-plane magnetic domains of the outer layers that develop at coercivity, we can suppress the supercurrent of the interlayer. We experimentally demonstrate a scaling of the magnetoresistance magnitude that we reproduce with a closed-form phenomenological formula that incorporates relevant macroscopic parameters and microscopic length scales of the superconducting and ferromagnetic structural units. The generic approach introduced here can be used to design novel cryogenic devices that completely switch the supercurrent 'on' and 'off', thus exhibiting the ultimate magnetoresistance magnitude 100% on a regular basis.
... For instance, Rong et al. found that hybrid-structure devices with three current leads improved the magnetoresistance value by a factor of 2.4–3.7 times [11]. Hewett et al. demonstrated that a geometry containing a multibranched metallic inclusion displayed a 2-order-of-magnitude increase in magnetoresis- tance [12]. Additionally, the finite element method (FEM) proved to be an effective approach, which has shown very good agreement with experimental results [5, 13, 14]. ...
... The redistribution of current paths with the applied magnetic field is the main mechanism of the EMR effect. Specifically, with no magnetic field present, the large fraction of current flowing through the high-conductivity region produces a short-circuit system; in the presence of a large transverse magnetic field, the system converts into an open circuit due to the fact that the current is forced to flow around the semiconducting material with a significantly higher resistance [12]. Nevertheless, it should be noted that the experimental data obtained from the EMR device is an equivalent resistance that depends on the special position of the voltage probe contacts. ...
... Studies have shown that changing of the distance between two voltage probe contacts produce different EMR effect results; however, there were no significant progresses superior to the conventional van der Pauw plate structure configuration in this way [18, 19] . Nevertheless , some special structure configurations can address the above issues to fabricating efficient EMR devices [12]. Here, some new structures are proposed to be investigated in the FEM models and compared with traditional designs. ...
The performance of extraordinary magnetoresistance (EMR) depends on the material parameters, hybrid structure design, contacts configuration, and manufacturing technology. In this paper, we pay close attention to the hybrid structure of the EMR device. A semiconductor-metal hybrid model based on the finite element method (FEM) is constructed to study the EMR effect, and the results show good agreement with the experimental data. The analysis of the van der Pauw plate structure indicates that the relationship between the two voltage probe contacts and the different EMR structures is the key factor to the design optimization. Accordingly, we find that the elliptic inclusion configurations improve the performance of the van der Pauw structure of EMR devices within a wide range of applied magnetic field (0-5 T). The bar-type and multibranched inclusion structures are subsequently optimized based on this principle. The new structures show excellent performance; more specifically, the modified multibranched inclusion structure displays a 2-fold increase in the magnetoresistance at 0.1 T and more than 2-order-of-magnitude increase at 5 T when compared with the original structure.
... Therefore, in most models the thickness is neglected and the device is considered to be two-dimensional (2D). Moussa et al. were the first to introduce a reduced, two-dimensional, diffusive transport model [23], and, since then, most of the simulation results have been obtained by employing only 2D models [24][25][26][27][28]. However, in some cases, especially when the 3-dimensional (3D) current distribution needs to be considered, a full 3D transport model has to be used. ...
... With this method, the optimized geometry was identified by the maximum sampling value of the applied current at the semiconductor/metal interface [22]. Recently, Hewett and Kusmartsev investigated a vdP disk with a multi-branched, metallic shunt and obtained an EMR effect two orders of magnitude greater then with a vdP disk with a concentric, circular, metallic shunt [25]. By extending the inhomogeneity further into random, metallic islands, using a random branch model, it was revealed that the large MR effect found in silver chalcogenides is basically an EMR effect [33]. ...
... It is of note that, no matter which geometry, the MR curves change from a quadratic dependence at low-field to a quasi-linear one at high-field and eventually saturate [17,25]. Branford et al. compared the EMR effect in the hybrid vdP disk with the MR effect in another disk-type geometry, the Corbino disk, with the same dimension. ...
The Extraordinary Magnetoresistance (EMR) effect is a change in the resistance of a device upon the application of a magnetic field in hybrid structures, consisting of a semiconductor and a metal. The underlying principle of this phenomenon is a change of the current path in the hybrid structure upon application of a magnetic field, due to the Lorentz force. Specifically, the ratio of current, flowing through the highly conducting metal and the poorly conducting semiconductor, changes. The main factors for the device's performance are: the device geometry, the conductivity of the metal and semiconductor, and the mobility of carriers in the semiconductor. Since the discovery of the EMR effect, much effort has been devoted to utilize its promising potential. In this review, a comprehensive overview of the research on the EMR effect and EMR devices is provided. Different geometries of EMR devices are compared with respect to MR ratio and output sensitivity, and the criteria of material selection for high-performance devices are discussed.
... This effect is an extrinsic property that depends on the shape of the device and the placement of the electric contacts. Previous studies that have investigated the influence of contact configurations and the geometry of the metallic region on the performance of the EMR device, have evaluated the device based on the EMR effect [15]- [18]. However, a more important parameter for sensing applications is the output sensitivity, which has not been considered so far. ...
