Magnetoresistance In Spin Valves Research Articles

Antisymmetric Magnetoresistance in a CrTe2/Bi2Te3/CrTe2 van der Waals Heterostructure Grown by MBE.

The magnetoresistance (MR) of spin valves usually displays a symmetric dependence on the magnetic field. An antisymmetric MR phenomenon has been discovered recently that breaks field symmetry and has the potential to realize polymorphic memory. In this work, centimeter-size and high-quality CrTe2/Bi2Te3/CrTe2 van der Waals (vdWs) heterostructure devices have been prepared using molecular beam epitaxy (MBE). By changing the magnetization direction of the top and bottom layers of CrTe2, an antisymmetric MR effect with high, intermediate, and low resistance states has been found and persists up to 75K. The emergence of this antisymmetric MR phenomenon is attributed to the spin Hall effect, which generates spin currents with both spin-up and spin-down orientations on the upper and lower surfaces of Bi2Te3. The spin currents diffuse or reflect at the Bi2Te3/CrTe2 interfaces alongside the additional charge currents induced by the inverse spin Hall effect (ISHE). Through theoretical calculations, the existence of the antisymmetric MR effect has also been confirmed. Our work emphasizes the use of the MBE technology to grow vdWs heterostructures to explore new physical phenomena and potential applications of spin electronic devices in polymorphic solid-state storage.

Large magnetoresistance and spin negative differential resistance in photoisomers-based molecular spin valves

By using non-equilibrium Green's functions in combination with density functional theory, the spin transport properties of photoisomers-based molecular spin valves constructed by salicylidene methylamine connected with two cobalt-dibenzotetraaza[14]annulene (Co-DBTAA) complex molecules via acetylene linkers are explored. A large magnetoresistance (MR) effect with a MR ratio larger than 104 can be observed in the molecular spin valves whether salicylidene methylamine is in the cis-enol form or the trans-keto form. Moreover, spin negative differential resistance (NDR) effects are also observed in the photoisomers-based molecular spin valves. The spin transport mechanisms are explored for MR and spin NDR effects observed in the molecular spin valves.

A GMR enzymatic assay for quantifying nuclease and peptidase activity.

Hydrolytic enzymes play crucial roles in cellular processes, and dysregulation of their activities is implicated in various physiological and pathological conditions. These enzymes cleave substrates such as peptide bonds, phosphodiester bonds, glycosidic bonds, and other esters. Detecting aberrant hydrolase activity is vital for understanding disease mechanisms and developing targeted therapeutic interventions. This study introduces a novel approach to measuring hydrolase activity using giant magnetoresistive (GMR) spin valve sensors. These sensors change resistance in response to magnetic fields, and here, they are functionalized with specific substrates for hydrolases conjugated to magnetic nanoparticles (MNPs). When a hydrolase cleaves its substrate, the tethered magnetic nanoparticle detaches, causing a measurable shift in the sensor's resistance. This design translates hydrolase activity into a real-time, activity-dependent signal. The assay is simple, rapid, and requires no washing steps, making it ideal for point-of-care settings. Unlike fluorescent methods, it avoids issues like autofluorescence and photobleaching, broadening its applicability to diverse biofluids. Furthermore, the sensor array contains 80 individually addressable sensors, allowing for the simultaneous measurement of multiple hydrolases in a single reaction. The versatility of this method is demonstrated with substrates for nucleases, Bcu I and DNase I, and the peptidase, human neutrophil elastase. To demonstrate a clinical application, we show that neutrophil elastase in sputum from cystic fibrosis patients hydrolyze the peptide-GMR substrate, and the cleavage rate strongly correlates with a traditional fluorogenic substrate. This innovative assay addresses challenges associated with traditional enzyme measurement techniques, providing a promising tool for real-time quantification of hydrolase activities in diverse biological contexts.

Magnetoresistance in Organic Spin Valves Based on Acid‐Exfoliated 2D Covalent Organic Frameworks Thin Films

AbstractCovalent organic frameworks (COFs), as a burgeoning class of crystalline porous materials, have made significant progress in their application to optoelectronic devices such as field‐effect transistors, memristors, and photodetectors. However, the insoluble features of microcrystalline two‐dimensional (2D) COF powders limit development of their thin film devices. Additionally, the exploration of spin transport properties in this category of π‐conjugated skeleton materials remains vacant thus far. Herein, an imine‐linked 2D Py‐Np COF nanocrystalline powder was synthesized by Schiff base condensation of 4,4′,4′′,4′′′‐(pyrene‐1,3,6,8‐tetrayl)tetraaniline and naphthalene‐2,6‐dicarbaldehyde. Then, we prepared a large‐scale free‐standing Py‐Np COF film via a top‐down strategy of chemically assisted acid exfoliation. Moreover, high‐quality COF films acted as active layers were transferred onto ferromagnetic La0.67Sr0.33MnO3(LSMO) electrodes for the first attempt to fabricate organic spin valves (OSVs) based on 2D COF materials. This COF‐based OSV device with a configuration of LSMO/Py‐Np COF/Co/Au demonstrated a remarkable magnetoresistance (MR) value up to −26.5 % at 30 K. Meanwhile, the MR behavior of the COF‐based OSVs exhibited a highly temperature dependence and operational stability. This work highlights the enormous application prospects of 2D COFs in organic spintronics and provides a promising approach for developing electronic and spintronic devices based on acid‐exfoliated COF thin films.

Magnetoresistance in Organic Spin Valves Based on Acid-Exfoliated 2D Covalent Organic Frameworks Thin Films.

Covalent organic frameworks (COFs), as a burgeoning class of crystalline porous materials, have made significant progress in their application to optoelectronic devices such as field-effect transistors, memristors, and photodetectors. However, the insoluble features of microcrystalline two-dimensional (2D) COF powders limit development of their thin film devices. Additionally, the exploration of spin transport properties in this category of π-conjugated skeleton materials remains vacant thus far. Herein, an imine-linked 2D Py-Np COF nanocrystalline powder was synthesized by Schiff base condensation of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraaniline and naphthalene-2,6-dicarbaldehyde. Then, we prepared a large-scale free-standing Py-Np COF film via a top-down strategy of chemically assisted acid exfoliation. Moreover, high-quality COF films acted as active layers were transferred onto ferromagnetic La0.67 Sr0.33 MnO3 (LSMO) electrodes for the first attempt to fabricate organic spin valves (OSVs) based on 2D COF materials. This COF-based OSV device with a configuration of LSMO/Py-Np COF/Co/Au demonstrated a remarkable magnetoresistance (MR) value up to -26.5 % at 30 K. Meanwhile, the MR behavior of the COF-based OSVs exhibited a highly temperature dependence and operational stability. This work highlights the enormous application prospects of 2D COFs in organic spintronics and provides a promising approach for developing electronic and spintronic devices based on acid-exfoliated COF thin films.

Co/Pd-based spin-valves with perpendicular magnetic anisotropy on flexible substrates. Direct deposition vs transfer-and-bonding approaches

Flexible spintronics is an emerging field of research that has received increasing attention due to the additional functionalities that are allowed (lightweight, flexibility, shape-ability, wearability) with respect to conventional rigid systems. In this work, different strategies for the fabrication of flexible spintronic devices with perpendicular magnetic anisotropy are compared, i.e., transfer-and-bonding approaches exploiting wet and dry lift-off methods, and direct deposition on flexible substrates. To evaluate the potential of the proposed strategies, Co/Pd-based giant magneto-resistive spin-valves including a synthetic antiferromagnet reference electrode were investigated. Such stacks represent a demanding model system, owing to the large number of interfaces whose quality strongly affects the overall magnetic and electric performances. The advantages and drawbacks of the different strategies are discussed to provide crucial indications for the development of flexible spintronic devices of any complexity. Based on the results, the most suitable option for achieving high-quality heterostructures on large area surfaces via direct deposition is using polyethylene naphthalate (Teonex®) tapes, provided that the processing and operating temperatures are relatively low (<525 K). On the other hand, if the process requires higher temperatures, the dry lift-off method exploiting the low adhesion between an Au underlayer and the SiOx/Si(100) substrate is the preferred alternative.

Giant magnetoresistance (GMR) spin-valve based magnetic sensor with linear and bipolar characteristics for low current detection

High sensitivity linear, bipolar, and hysteresis-free magnetic field sensor is necessary for low current measurement of the order of 1000 mA with a resolution of 1 mA. Magnetoresistive technology has evolved into popular magnetic sensing technology where magnetic multilayered structures were tailored to obtain linear output characteristics. In this report, a GMR spin-valve structure was used to develop magnetic field sensing elements. Mechanical assembly of the sensing elements in the form of a Wheatstone bridge configuration was made to have the linear and bipolar characteristics of the sensor. Application of the constant DC biasing field perpendicular to the sensitivity axis was made to have fully hysteresis-free output characteristics and the maximum sensitivity was achieved of the order 2 to 2.5 mV/G with a supply of 1 mA current to the bridge circuit. The in-house developed spin valve sensor was then used to measure the current in the range of ± 1 A, having a sensitivity of the order of 2 mV/mA with a resolution down to 1 mA by using non-intrusive current sensing technology. A core-based sensor has a large aperture size that accommodates a current-carrying conductor with an ampacity of 1 kA. The calibrated output shows the sensor can measure the field in the range of ± 0.4 mT with a resolution of ∼ 200 nT and has the potential for floating current measurement application in the battery management system.

Nearly perfect spin-filtering effect with tunable spin-polarization direction and huge magnetoresistance in molecular spin valves

Spin-transport properties of molecular spin valves constructed by two chromium-salophene (CrSal) molecules connected with boron nitride (BN) atomic chains are investigated by applying a nonequiblium Green's function method with density functional theory. Nearly perfect spin-filtering effect can be found when the molecular spin valves are set in parallel magnetic configuration. In particular, the direction of the detected spin-polarization signal is reversible by tuning the types of BN atomic chains. Moreover, obvious magnetoresistance (MR) effects are also found in the molecular spin valves. More importantly, the MR ratio can be changed from about 359% to about 1.31×105% by adjusting the types of BN atomic chains. Our work provides a new avenue to realize high-performance multifunctional molecular spin valves.

Half-Metallic Heusler Alloy/MoS2 Based Magnetic Tunnel Junction.

Integration of half-metallic materials and 2D spacers into vertical magnetoresistive spin valves may pave the way for effective low-power consumption storage and memory technologies. Driven by the recent successful growth of graphene/half-metallic Co2Fe(Ge1/2Ga1/2) (CFGG) heterostructure, here we report a theoretical investigation of magnetic tunnel junction (MTJ) based on the ferromagnetic CFGG Heusler alloy and the MoS2 spacer of different thicknesses. Using ab initio approach, we demonstrate that the inherent ferromagnetism of CFGG is preserved at the interface, while its half-metallicity is recovering within few atomic layers. Ballistic transport in CFGG/MoS2/CFGG MTJ is studied within the nonequilibrium Green's function formalism, and a large magnetoresistance value up to ∼105% is observed. These findings support the idea of effective spintronics devices based on half-metallic Heusler alloys and highly diversified transition metal dichalcogenide family.

Thin-Film Heterostructures Based on Co/Ni Synthetic Antiferromagnets on Polymer Tapes: Toward Sustainable Flexible Spintronics.

Synthetic antiferromagnets with perpendicular magnetic anisotropy (PMA-SAFs) have gained growing attention for both conventional and next-generation spin-based technologies. While the progress of PMA-SAF spintronic devices on rigid substrates has been remarkable, only few examples of flexible thin-film heterostructures are reported in the literature, all containing platinum group metals (PGMs). Systems based on Co/Ni may offer additional advantages with respect to devices containing PGMs, i.e., low damping and high spin polarization. Moreover, limiting the use of PGMs may relieve the demand for critical raw materials and reduce the environmental impact of related technologies, thus contributing to the transition toward a more sustainable future. Here, we discuss for the first time the realization of Co/Ni-based PMA-SAFs on polymer tapes and exploit it to obtain flexible giant magneto-resistive spin valves (GMR-SVs) with perpendicular magnetic anisotropy. Several combinations of buffer and capping layers (i.e., Pt, Pd, and Cu/Ta) are also investigated. High-quality flexible SAFs with a fully compensated antiferromagnetic region and SVs with a sizable GMR ratio (up to 4.4%), in line with the values reported in the literature for similar systems on rigid substrates, were obtained in all cases. However, we demonstrate that PGMs allows achieving the best results when used as a buffer layer, while Cu is the best choice as a capping layer to optimize the properties of the stacks. We justify the role of buffer and capping layers in terms of different interdiffusion mechanisms occurring at the interface between the metallic layers. These results, along with the high robustness of the samples' properties against bending (up to 180°), indicate that complex and bendable Co/Ni-based heterostructures with reduced content of PGMs can be obtained on flexible tapes, allowing for the development of novel flexible and sustainable spintronic devices for applications in many fields including wearable electronics, soft robotics, and biomedicine.

Tunnel magnetoresistance of trilayer graphene-based spin valve

Using the non-equilibrium Green’s function method and within the framework of the tight-binding Hamiltonian model in Landauer–Büttiker formalism, the spin-dependent transport and tunnel magnetoresistance ( T M R ) of AAA- and ABC-stacked trilayer zigzag graphene nanoribbon (TLG) connected to two ferromagnetic ( F M ) semi-infinite single-layer zigzag graphene nanoribbons (FM/TLG/FM system) have been theoretically investigated. Results show that the T M R for both AAA- and ABC-stacked cases can be increased about 100% because of the band-selective rule, and the magnitude of this 100% T M R region, enhances with the increase of the magnetization strength in FM graphene nanoribbon electrodes . Also, the TLG dimension has a prominent effect on the T M R ratio of the system. It is shown that the large values of the TMR ratio can be achieved very nicely by the variation of the width and length of the FM/TLG/FM system. The present theoretical results may be useful for designing few-layer graphene-based spin valves . • The TMR of trilayer graphene-based spin valve have been investigated. • The TMR for both AAA- and ABC-stacked cases can be increased about 100%. • The magnitude of 100% TMR region enhances with the magnetization strength. • The effects of width and length on the TMR ratio have been investigated.

Molecular and Interfacial Adjustment of Magnetoresistance in Organic Spin Valves Using Isoindigo-Based Polymers

Molecular and Interfacial Adjustment of Magnetoresistance in Organic Spin Valves Using Isoindigo-Based Polymers

Giant magnetoresistance in spin valves realized by substituting Y-site atoms in Heusler lattice

‘All-Heusler’ spin-valve constructed by two half-metallic Heusler electrodes and a non-magnetic Heusler spacer contains two interfaces that have a crucial influence on the magnetoresistance. In order to reduce the disorder at the interface and protect the half metallicity of the electrode at the same region, we propose a scheme to construct a spin valve by replacing the Y-site atoms in the half-metallic Heusler electrode to obtain the corresponding non-magnetic spacer based on the Slater–Pauling rule. In this way, the lattice and band match of the two materials can be ensured naturally. By using Co2FeAl as electrode and Co2ScAl as the spacer materials, we construct the Co2FeAl/Co2ScAl/Co2FeAl(001)-spin valve. Based on the first-principles calculation, the most stable FeAl/CoCo-interface is determined both from the phonon spectra and the formation energy when the spacer Co2ScAl grows on the FeAl-terminated (001) surface of electrode material Co2FeAl. By comparing the projected density of states of the interfacial atoms with the corresponding density of states of the bulk electrode material, only the value of spin-up state of Al changes from 0.17 states/atom/eV to 0.06 states/atom/eV before and after substitution, the half metallicity at the interface is maintained. As a result, the spin-dependent transport properties show significant theoretical magnetoresistance MRop which can reach up to 1010% and much larger than 106% reported before.

Length dependence of magnetoresistance in organic spin valves

With the Su–Schrieffer–Heeger model and Green's function method, the length dependence of magnetoresistance in organic spin valves is calculated in the frame of tunneling transport. Based on different energy level alignments between the molecule and the electrodes, the length effect on the magnetoresistance is investigated in three transport schemes, barrier tunneling, resonant tunneling, and transition between them. In the first scheme, a length-induced exponential or linear decline of the magnetoresistance is obtained. An oscillation and nonlinear dependence are observed in the second and third schemes. The mechanism is explained by investigating the transmission spectra at different lengths, where the evolution of the efficient transmission in the bias window with length differs in different schemes. The results agree with many experimental measurements qualitatively.

Influence of Cr interlayer with different thickness on transition of magnetoresistance effect of Gd/FeCo thin films

As one of the most representative features characterizing the spin valve structure, magnetoresistance is an important method to study the interlayer coupling in multilayers. Considering the induced magnetism of rare earth at room temperature due to the coupling and magnetic proximity effect in the structure of rare earth/magnetic transition metal, an intermediate nonmagnetic metal can be inserted to form the spin valve structure to regulate the interlayer coupling, which expands the scope of applications of rare earth in spintronics. In this work, the interlayer exchange coupling and interfacial effects of Gd (4 nm)/Cr (&lt;i&gt;t&lt;/i&gt;&lt;sub&gt;Cr&lt;/sub&gt;)/FeCo (5 nm) trilayers with different Cr layer thickness (&lt;i&gt;t&lt;/i&gt;&lt;sub&gt;Cr&lt;/sub&gt;) are studied by means of in plane magnetoresistance. Compared with FeCo film, Gd/FeCo film obtains more obvious anisotropic magnetoresistance. While the magnetoresistance value obtained for the configuration of &lt;i&gt;I&lt;/i&gt;⊥&lt;i&gt;H&lt;/i&gt; shows a minimum value at the peak due to the insertion of Cr layer, and this minimum value becomes more pronounced with the increase of &lt;i&gt;t&lt;/i&gt;&lt;sub&gt;Cr&lt;/sub&gt;. When&lt;i&gt; t&lt;/i&gt;&lt;sub&gt;Cr&lt;/sub&gt; = 3 nm, the negative spin valve effect almost totally overcomes the anisotropic-magnetoresistance effect. Different spin asymmetries of scattering that are formed in FeCo layer and Cr/Gd layers are mainly responsible for creating the negative spin valve magnetoresistance, in which the resistance becomes smaller near the coercive, while the resistance becomes larger at high field parallel to magnetic moment. The oscillation of magnetoresistance with &lt;i&gt;t&lt;/i&gt;&lt;sub&gt;Cr&lt;/sub&gt; at &lt;i&gt;I&lt;/i&gt; // &lt;i&gt;H&lt;/i&gt; and the hysteresis loops at 5 K further confirm the existence of interlayer coupling both at room temperature and 5 K.

Spin valve effect in two-dimensional VSe[formula omitted] system

Vanadium based dichalcogenides, VSe2, are two-dimensional materials in which magnetic Vanadium atoms are arranged in a hexagonal lattice and are coupled ferromagnetically within the plane. However, adjacent atomic planes are coupled antiferromagnetically. This provides new and interesting opportunities for application in spintronics and data storage and processing technologies. A spin valve magnetoresistance may be achieved when magnetic moments of both atomic planes are driven to parallel alignment by an external magnetic field. The resistance change associated with the transition from antiparallel to parallel configuration is qualitatively similar to that observed in artificially layered metallic magnetic structures. Detailed electronic structure of VSe2 was obtained from DFT calculations. Then, the ballistic spin-valve magnetoresistance was determined within the Landauer formalism. In addition, we also analyze thermal and thermoelectric properties. Both phases of VSe2, denoted as H and T, are considered.

Temperature dependent transition of conduction mechanism from carrier injection to multistep tunneling in Fe3O4 (111)/Alq3/Co organic spin valve

We have presented experimental results addressing the origin of spin valve (SV) magneto-resistance (MR), in both injection and tunnel conduction regimes, in our fabricated Fe 3 O 4 (111)/Alq 3 /Co SV device. Experimental evidences have shown that any alternative MR process, such as ‘tunneling anisotropic MR’ is not at the origin of this SV MR. Spin resolved density of states of electrodes indicate that both the conduction mechanisms induce different spin dependent scattering which inturn modify the MR signal of the device. This modification helped in maintaining a non-monotonous quenching of MR signal with increase in temperature. We have also proposed a phenomenological model for device operation where the concept of charge gap modification at Fermi level across Verwey transition is envisaged to offer this unique scenario of tuning the conduction mode and hence MR in this ferrite based organic SV. The model is also supported by an established theoretical study which considers high temperature phonon assisted tunneling through defect states at electrode–organic interface of the device. • Conduction mechanism transition from carrier injection to multistep tunneling. • Transition due to Verwey transition of Fe 3 O 4 . • Spin flip scattering at Alq 3 spacer above Verwey transition temperature. • Non-monotonous MR quenching with temperature. • Room temperature MR signal of hybrid spin valve.

A Soft Tactile Sensor Based on Magnetics and Hybrid Flexible-Rigid Electronics.

Tactile sensing is crucial for robots to manipulate objects successfully. However, integrating tactile sensors into robotic hands is still challenging, mainly due to the need to cover small multi-curved surfaces with several components that must be miniaturized. In this paper, we report the design of a novel magnetic-based tactile sensor to be integrated into the robotic hand of the humanoid robot Vizzy. We designed and fabricated a flexible 4 × 2 matrix of Si chips of magnetoresistive spin valve sensors that, coupled with a single small magnet, can measure contact forces from 0.1 to 5 N on multiple locations over the surface of a robotic fingertip; this design is innovative with respect to previous works in the literature, and it is made possible by careful engineering and miniaturization of the custom-made electronic components that we employ. In addition, we characterize the behavior of the sensor through a COMSOL simulation, which can be used to generate optimized designs for sensors with different geometries.

Length-induced large magnetoresistance in polyacene molecular spin valves

With the help of first-principles method, an unusual length effect in polyacene molecular spin valves is revealed. It is found that beyond a critical length, the magnitude of tunneling magnetoresistance is significantly enhanced from 10% to 2500%. Theoretical analysis demonstrates that such significant increase of magnetoresistance is related to the nonmagnetic-antiferromagnetic phase transition of polyacene molecules, which is determined by the relative magnetization orientation of the ferromagnetic electrodes. The molecular gap shows distinct length dependence with the change of molecular magnetic state, which keeps decreasing with length in the nonmagnetic state while a fine gap is obtained in the antiferromagnetic state. This work indicates a valid way to obtain considerable tunneling magnetoresistance in long molecular spin valves.

Angular dependent magnetoresistance in organic spin valves

Vertical organic spin valve (OSV)-based organic spintronic devices with additional degree of freedom to utilize and control the magnetoresistance (MR) by spin of electrons, have attracted a lot of interests for both foundation science and future functional device applications. Herein the effects of temperature, bias voltage and direction of magnetic field on the MR of the OSV are investigated to disclose the mechanisms. Specifically, the MR shows angular dependence with the value tuned from negative to positive by rotating the field direction from in-plane to out-of-plane, corresponding to the angular dependent spin moment. A domain-switch model is proposed to simulate the resistance changes in OSV device. The research provides a new route to tune the MR in organic spintronic devices, which is significant for future functional device applications.