Out-of-plane magnetoresistance in ferromagnet/graphene/ferromagnet spin-valve junctions (original) (raw)
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Spin valve effect of NiFe/graphene/NiFe junctions
Nano Research, 2013
When spins are injected through graphene layers from a transition metal ferromagnet, high spin polarization can be achieved. When detected by another ferromagnet, the spin-polarized current makes high-and low-resistance states in a ferromagnet/graphene/ferromagnet junction. Here, we report manifest spin valve effects from room temperature to 10 K in junctions comprising NiFe electrodes and an interlayer made of double-layer or single-layer graphene grown by chemical vapor deposition. We have found that the spin valve effect is stronger with double-layer graphene than with single-layer graphene. The ratio of relative magnetoresistance increases from 0.09% at room temperature to 0.14% at 10 K for single-layer graphene and from 0.27% at room temperature to 0.48% at 10 K for double-layer graphene. The spin valve effect is perceived to retain the spin-polarized transport in the vertical direction and the hysteretic nature of magnetoresistance provides the basic functionality of a memory device. We have also found that the junction resistance decreases monotonically as temperature is lowered and the current-voltage characteristics show linear behaviour. These results revealed that a graphene interlayer works not as a tunnel barrier but rather as a conducting thin film between two NiFe electrodes.
The effect of a copper interfacial layer on spin injection from ferromagnet to graphene
Applied Physics A, 2013
Aiming at enhancing the spin-injection efficiency from ferromagnet to graphene, graphene-based spin valve devices with ferromagnet-Cu-graphene contacts have been fabricated and studied. The ferromagnet-Cu-graphene contact has attracted our attention because of the spin-preserving characteristic of ferromagnet-Cu interface and possible presence of moderate potential barrier at the Cugraphene interface. The latter may help to alleviate the conductance mismatch issue in spin injection from ferromagnet to graphene. Devices with or without Cu interfacial layers have been fabricated by both evaporation and sputtering on mechanically exfoliated graphene sheets. A potential barrier of 33 meV was derived for the Cugraphene interface in evaporation-deposited devices from the temperature-dependence of contact resistance. On the other hand, pure ferromagnet-graphene contact exhibits a much lower contact resistance due to its chemisorption interface with graphene. Nonlocal magnetoresistance measurements showed a moderate enhancement of spin injection efficiency with the aid of the Cu interfacial layer.
A perpendicular graphene/ferromagnet electrode for spintronics
Applied Physics Letters, 2020
We report on the large-scale integration of graphene layers over a FePd perpendicular magnetic anisotropy (PMA) platform, targeting further downscaling of spin circuits. An L10 FePd ordered alloy showing both high magneto-crystalline anisotropy and a low magnetic damping constant, is deposited by magnetron sputtering. The graphene layer is then grown on top of it by large-scale chemical vapor deposition. A step-by-step study, including structural and magnetic analyses by x-ray diffraction and Kerr microscopy, shows that the measured FePd properties are preserved after the graphene deposition process. This scheme provides a graphene protected perpendicular spin electrode showing resistance to oxidation, atomic flatness, stable crystallinity, and perpendicular magnetic properties. This, in turn, opens the way to the generalization of hybrid 2D-materials on optimized PMA platforms, sustaining the development of spintronics circuits based on perpendicular spin-sources as required, for i...
Materials Research Express, 2020
One of the most prominent and effective applications of graphene in the field of spintronics is its use as a spacer layer between ferromagnetic metals in vertical spin valve devices, which are widely used as magnetic sensors. The magnetoresistance in such devices can be enhanced by a selection of suitable spacer materials and proper fabrication procedures. Here, we report the use of dry-transferred single- and double-layer graphene, grown by chemical vapor deposition (CVD), as the spacer layer and the fabrication procedure in which no photo-resist or electron-beam resists is used. The measured maximum magnetoresistance of NiFe/CVD-Graphene/Co junction is 0.9% for the single- and 1.2% for the double-layer graphene at 30 K. The spin polarization efficiency of the ferromagnetic electrodes is about 6.7% and 8% for the single- and the double-layer graphene, respectively, at the same temperature. The bias-independent magnetoresistance rules out any contamination and oxidation of the inter...
14th IEEE International Conference on Nanotechnology, 2014
Magnetoresistance (MR), the change in electrical resistance of a solid-state system due to an external magnetic field, is a key effect in condensed matter physics, both for fundamental understanding of charge transport phenomena, as well as immense commercial implications. Artificial layered structures often exhibit strong magnetoresistance (MR) effects that are exploited in various data storage and magnetic field sensing technologies. Graphite is a naturally occurring layered structure in which single graphitic layers (or "graphene") are stacked up on each other. Magnetoresistance (MR) in graphitic systems (single to few layers of graphene and bulk graphite) has drawn significant attention in recent years. It has been theoretically predicted that multilayer graphene (MLG) on Ni can potentially exhibit large magnetoresistance values due to spin filtering effect. However, experimental work in this area is rare. The purpose of this work is to explore various magnetoresistance effects in MLG/Ni systems. Multilayer graphene (MLG) stacks with various thicknesses have been grown on polycrystalline Ni substrates using a standard chemical vapor deposition (CVD) recipe. These samples exhibit a large, negative MR effect in current-perpendicularto-plane (CPP) geometry with the magnetic field normal to the plane. A negative magnetoresistance effect ~ 10 4 % has been observed, which persists even at room temperature. The observed magnetoresistance is extremely high as compared to other known materials systems for similar temperature and field range. This effect is correlated with the shape of the 2D peak as well as with the absence of D peak in the Raman spectrum. The observed data is qualitatively consistent with the iii "interlayer magnetoresistance" (ILMR) mechanism in which interlayer charge transfer occurs between the zero mode Landau levels of weakly coupled graphene layers. To further understand ILMR effect, angle and thickness dependent studies have been performed in as-grown MLG on Ni samples. Angular dependences of ILMR effect in as-grown MLG agree well with theory. However, the angular response is sharper than expected and is related to the additional sources of positive MR present in the system. In addition, the ILMR effect persists and becomes stronger as thickness of MLG is increased. Interestingly, for larger thickness samples, magnitude of the MR effect is relatively insensitive to temperature. To further verify this, CPP MR measurements have been performed in as-grown MLG samples with different thicknesses. In the next stage of this thesis, as-grown MLG samples have been tested in spin valve configuration in order to investigate spin-related magnetoresistance effects and its implications for graphene spin filters. However these devices only show weak localization and ILMR but no spin filtering. Based on above observations, we are planning to explore the following subprojects in future: (1) MR effects in as-grown MLG on cobalt (Co), (2) MR effects in functionalized graphene/Ni (111) and exploring spin filtering effect in this system, and (3) MR effects in transferred MLG on flexible substrates. Due to large MR value and its persistence at room temperature, this ILMR effect in as-grown MLG samples is expected to have commercial implications and encourage further research on MLG physics and MLG growth mechanisms on iv ferromagnetic substrate. Further, intrinsic compatibility of MLG with flexible electronics and sensorics makes ILMR an exciting platform for future magnetic sensing and data storage technologies.
Atomic-Scale Interfacial Magnetism in Fe/Graphene Heterojunction
Successful spin injection into graphene makes it a competitive contender in the race to become a key material for quantum computation, or the spin-operation-based data processing and sensing. Engineering ferromagnetic metal (FM)/graphene heterojunctions is one of the most promising avenues to realise it, however, their interface magnetism remains an open question up to this day. In any proposed FM/graphene spintronic devices, the best opportunity for spin transport could only be achieved where no magnetic dead layer exists at the FM/graphene interface. Here we present a comprehensive study of the epitaxial Fe/graphene interface by means of X-ray magnetic circular dichroism (XMCD) and density functional theory (DFT) calculations. The experiment has been performed using a specially designed FM 1 /FM 2 /graphene structure that to a large extent restores the realistic case of the proposed graphene-based transistors. We have quantitatively observed a reduced but still sizable magnetic moments of the epitaxial Fe ML on graphene, which is well resembled by simulations and can be attributed to the strong hybridization between the Fe 3d z2 and the C 2p z orbitals and the sp-orbital-like behavior of the Fe 3d electrons due to the presence of graphene.
Journal of Applied Physics, 2011
We study spin transport in bilayer graphene structures where gate electrodes are attached to ferromagnetic graphene. Due to the exchange field in the gated regions, the current becomes spin dependent and can be controlled by tuning the gate voltages. It is shown that thanks to strong resonant chiral tunneling inherent in bilayer graphene, very high spin polarization and tunneling magnetoresistance can be achieved in the considered structures. Different possibilities for controlling the spin current are discussed. The study demonstrates the potential of bilayer graphene structures for spintronic applications with significant improvement over previously predicted results in monolayer graphene structures.
Physics Letters A, 2019
In this study we carried out first principle calculations for spin dependent electronic transport in our proposed spintronic device consisting of graphene nanoribbon as scattering region with cobalt electrodes and magnesium oxide as tunneling barrier. The I-V Characteristics are calculated by using Non-Equilibrium Green's Function formalism in combination with Semi-Empirical (SE) Extended Huckel Theory (EHT) using Atomistic Tool Kit software at room temperature. The high value of GMR (Giant Magnetoresistance) is recommended for spintronic devices. The results reveal that the device shows a very high GMR ratio of 5.16 × 10 4 %. The device also shows very low off state current, therefore negligible off state power consumption. The investigation of spin dependent non equilibrium transport is done by examining bias dependent transmission coefficients. Furthermore, some basic logic gates, like NOT, AND and NOR have been realized from the modeled device. The device may also find applications in data storage, magnetic field sensors etc.
Electronics, 2013
Current-perpendicular-to-plane (CPP) magnetoresistance (MR) effects are often exploited in various state-of-the-art magnetic field sensing and data storage technologies. Most of the CPP-MR devices are artificial layered structures of ferromagnets and non-magnets, and in these devices, MR manifests, due to spin-dependent carrier transmission through the constituent layers. In this work, we explore another class of artificial layered structure in which multilayer graphene (MLG) is grown on a metallic substrate by chemical vapor deposition (CVD). We show that depending on the nature of the graphene-metal interaction, these devices can also exhibit large CPP-MR. Magnetoresistance ratios (>100%) are at least two orders of magnitude higher than "transferred" graphene and graphitic samples reported in the literature, for a comparable temperature and magnetic field range. This effect is unrelated to spin injection and transport and is not adequately described by any of the MR mechanisms known to date. The simple fabrication process, large magnitude of the MR and its persistence at room temperature make this system an attractive candidate for magnetic field sensing and data storage applications and, also, underscore the need for further fundamental investigations on graphene-metal interactions.
Nature Communications, 2018
Graphene has remarkable opportunities for spintronics due to its high mobility and long spin diffusion length, especially when encapsulated in hexagonal boron nitride (h-BN). Here, we demonstrate gate-tunable spin transport in such encapsulated graphene-based spin valves with one-dimensional (1D) ferromagnetic edge contacts. An electrostatic backgate tunes the Fermi level of graphene to probe different energy levels of the spin-polarized density of states (DOS) of the 1D ferromagnetic contact, which interact through a magnetic proximity effect (MPE) that induces ferromagnetism in graphene. In contrast to conventional spin valves, where switching between high-and low-resistance configuration requires magnetization reversal by an applied magnetic field or a high-density spin-polarized current, we provide an alternative path with the gate-controlled spin inversion in graphene.