Spin Valve Research Articles

Impact of material and tunnel barrier quality on spin transport in a CVD graphene non-local spin valve device array

Wafer-scale graphene films produced via chemical vapor deposition (CVD) are now commercially available, however these films inherently contain randomly distributed defects such as adlayers and grain boundaries. This report discusses the impact of these defects on the signal integrity of an array of graphene-based non-local spin valves (NLSVs). It was found that critical spin parameters fluctuate drastically between adjacent identical devices. Investigation of the channel quality indicated that adlayers do not affect spin signal significantly even when located directly in the spin transport region of the device. In contrast, grain boundary defects within the spin transport region have significant impact on spin signal. Poor tunnel barrier integrity due to residue from the fabrication process also remains a dominant factor driving device variability.

Simple solution processed spin switching in FeCo/Rubrene/NiFe spin valve device

Simple solution processed spin switching in FeCo/Rubrene/NiFe spin valve device

Role of interfacial layer on exchange-coupled magnetic properties of bi-magnetic nanostructures: An experimental and theoretical approach

Bi-magnetic hetero-nanostructures exhibiting significant exchange bias effects are highly desirable for technological advancement in spin valves, memory devices, data storage, biomedicine, and hyperthermia-based cancer treatment. As the interfacial spin interaction and the resulting anisotropy play a central role in these phenomena, investigating the tailored physical properties of hetero-structures of magnetically contrasting nanoparticles in different architectures is extremely useful. In this work, we report the formation of microspheres containing nano-aggregates of ferrimagnetic Fe3O4 and antiferromagnetic NiO phases. We demonstrate that this kind of bi-magnetic hetero-structures provide a conducive atmosphere for strong interfacial coupling giving rise to an extensive exchange bias effect (∼1.6 kOe). In addition, we also observe a substantial enhancement of the coercive field, indicating the onset of an additional unidirectional anisotropy under the field-cooled condition. Our first-principle density functional theory calculations reveal the role of cation intermixing at the interface of the two phases, being the source of an additional higher magneto-crystalline anisotropy than the original phases. This cation intermixing at the interface also causes a narrowed energy band, which was demonstrated by UV–Vis spectroscopy and first principle calculations. Having these technologically essential features with a tunable band gap, the embedded hetero-nanostructures are envisioned to cater to the requirement of high-density data storage and memory devices.

On-chip full bridge bipolar linear spin valve sensors through modified synthetic antiferromagnetic layers

Realizing the rising demand for high-sensitivity magneto-resistive (MR) sensors in the industry, an attempt was made towards the fabrication of a spin valve (SV) based bipolar sensor on chip in the form of a full Wheatstone bridge with push–pull configuration. For a sensor with a push–pull configuration, the opposite arms are configured with opposite sense layers. To achieve this, either odd or even layers of synthetic antiferromagnetic (SAF) structure were introduced in the conventional spin valve structure, through which the magnetization orientation of the sensing layer was regulated by either negative or positive sensitivity to the applied field direction respectively. A detailed theoretical simulation was carried out to achieve the stable antiparallel magnetic state around zero fields by varying individual layer thicknesses in the case of single and double-layer SAF structures. With optimized conditions, experimental data were presented, and a bipolar device with a sensitivity of the order of 0.7 mV/V/Oe in the linear field range of ± 15 Oe was fabricated. The performance of the device was characterized by a wider temperature range and it was observed that the device has high thermal stability in the range of - 40 °C to 125 °C with a thermal coefficient of the voltage around 12 μV/V/∘C. Angular performance of the fabricated sensor with minimized orthogonality error was presented and it was observed that the sensor can measure the angle with an accuracy of +/-2 ° .

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.

Electromagnetic field detectors based on spintronics devices

The paper proposes a model of an electromagnetic radiation sensor that uses the precession of the magnetization vector in a ferromagnet (ferromagnetic resonance) as a result of absorbing the energy of an incident electromagnetic wave, the generation of a spin current as a result of this precession, the generation of a spin-polarized current as a result of the passage of a spin current in a non-magnetic metal, and a change in the direction of magnetization of a ferromagnetic layer with a low coercive force (free layer) due to the passage of a spin-polarized current. Then the radiation will be detected by its effect on the electrical resistance of the entire structure, which depends on the mutual directions (parallel or antiparallel) of magnetization of the free and fixed (with a large coercive force) ferromagnetic layers (phenomenon of giant magnetic resistance). The dependence of the spin-polarized current in the device on the frequency and amplitude of the incident electromagnetic wave with linear polarization was calculated. A method of calculating the range of amplitude and frequency values of radiation that can be detected by the sensor has been developed. The parameters of this model are the detection time and the number of spin gates in one sensor. Calculations are given for a ferromagnetic layer made of permalloy and for spin valves with four different critical current values that determine the process of remagnetization of the free layer: 20, 50, 100, and 200 microamps.

Synthesis, characterization, and feasibility investigation of dysprosium-doped samarium iron oxide nano-powder/polydimethylsiloxane (Dy-SmFeO/PDMS) nano-composite for dynamic magneto-mechanical stability

In this study, the synthesis and characterization of a dysprosium-doped samarium iron oxide nano powder/polydimethylsiloxane (Dy-SmFeO/PDMS) nano-composite are described. The sol-gel citrate method was employed for the synthesis, yielding highly polycrystalline nano powders with a polymorphic distribution, as revealed by X-ray diffraction and Rietveld analysis. Raman spectroscopy was utilized to investigate the chemistry of the nano powders. Notably, the readings obtained using a vibrating sample magnetometer highlighted the intriguing ferromagnetic-to-antiferromagnetic coupling behavior of the samples. The field-emission scanning electron microscopy analysis indicated that the orthorhombic crystal surfaces were uniformly encapsulated by PDMS. Furthermore, a dynamic mechanical analysis was conducted under the influence of a magnetic field (1000 mT) revealed the excellent mechanical stability of the composite. This research highlights the potential of the Dy-SmFeO/PDMS composite as a promising magnetic material with desirable properties, opening up possibilities for various applications in fields such as micro-magnetic devices, sensors, spin valves, and actuators.

Slonczewski-spin-current driven dynamics of 180∘ domain walls in spin valves with interfacial Dzyaloshinskii–Moriya interaction

Steady-flow dynamics of ferromagnetic 180∘ domain walls (180DWs) in long and narrow spin valves (LNSVs) with interfacial Dzyaloshinskii–Moriya interaction (IDMI) under spin currents with Slonczewski factor are examined. Depending on the magnetization orientation of polarizers (pinned layers of LNSVs), dynamics of 180DWs in free layers of LNSVs are subtly manipulated: (i) for parallel polarizers, stronger spin polarization leads to higher Walker limit thus ensures the longevity of faster steady flows. Meantime, IDMI induces both the stable-region flapping and its width enlargement. (ii) For perpendicular polarizers, a wandering of 180DWs between bi- and tri-stability persists with the criticality adjusted by the IDMI. (iii) For planar-transverse polarizers, IDMI makes the stable region of steady flows completely asymmetric and further imparts a high saturation wall velocity under large current density. Under the last two polarizers, the ultrahigh differential mobility of 180DWs survives. The combination of Slonczewski spin current and IDMI provides various possibilities of fine controlling on 180DW dynamics, hence opens avenues for magnetic nanodevices with rich functionality and high robustness.

Exploring the structural and magnetic characteristics of ferrous ferric oxide nanoparticles doped with Ca2+ ions for nanoscale devices

In this study, we investigate the effect of Ca2+ substitution on the structural and magnetic characteristics of ferrous ferric oxide CaxFe3-xO4 (x = 0.2 and 0.4) nanoparticles produced by the sol–gel auto combustion method with citric acid as a fuel agent. X-Ray Diffraction (XRD) results show that the average crystallite size is in the range of 20–22 nm and lattice parameter decreases with increasing calcium concentration. Field Emission Scanning Electron Microscope (FESEM) image shows the crystalline nature of calcium-substituted ferrous ferric oxide nanoparticles. Electron Diffraction Spectra (EDS) confirms the presence of Fe, Ca, and O atoms in prepared sample. Vibrating Sample Magnetometer (VSM) measures the magnetic field at room temperature which confirm the existence of a superparamagnetic behavior of Ca2+ substituted ferrous ferric oxide nanoparticles which plays an essential role in nanoscale devices such as MRI, MRAM, spin valve, MTJ, and bio-sensing devices applications.

Study of the Effect of Inverse Magnetostriction in Ferromagnet/Ferroelectric Heterostructures Using Ab Initio Calculations

Fe/BaTiO3, Fe/SrTiO3, Co/BaTiO3, and Co/SrTiO3 heterostructures, which exhibit magnetoelectric effect, have been investigated. It is shown that the magnetic properties of thin ferromagnetic films can be controlled using an external electric field. The structural, electronic, and magnetic properties of the heterostructures have been investigated applying ab initio calculation methods. It is shown that, using the inverse piezoelectric effect, one can reduce the absolute value of the ferromagnet magnetization vector. This approach may be a basis for controlling the properties of one of the ferromagnetic layers of a superconducting spin valve and, as a consequence, the superconducting properties of the valve.

(Invited) Electrodeposition of Manganese Arsenides (MnxAs) as Promising Candidates in Spintronics

Spintronics is a new branch of electronics in which the spin of the electrons as well as their charge is manipulated to produce a desired outcome. Spintronic devices are particularly attractive for memory storage and magnetic sensor applications, and potentially for quantum computing where the electron spin would represent a bit of information. Nowadays many efforts are made to increase the efficiency and lower the production costs of these materials, among others the use of molecular inorganic compounds and cheap preparation techniques [1].Most of these layers are synthesized with physical and/or vapor phase techniques [2] which allow to obtain materials with a very few defects, but which are complex to manage and typically very expensive. For this reason, in this study we have searched for a way to electrochemically deposit a compound with interesting spintronic properties in the aqueous medium. In fact, electrodeposition is notoriously a very cheap, versatile and easily scalable technique.With this purpose Mn-As system was selected thanks to its good magnetic and transport properties to be used as building blocks for spin valve [3]. MnAs has potential applications in spintronics, for electrical spin injection into GaAs and Si based devices [4] and DFT simulations predict that Mn2As and Mn3As have a low magnetization saturation and a high spin polarization at the Fermi-level [5]. Starting from MnSO4 and NaAsO2 precursors solutions with various concentrations, supporting electrolytes and pH were tested.The electrochemical behaviour of the precursors was investigated with cyclic voltammetries and both potentiostatic as well as galvanostatic deposition were carried out. The deposits obtained were morphologically and compositional characterised with scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray fluorescence spectroscopy (XRF), the chemical states were analysed with X-ray photoelectron spectroscopy (XPS), the crystalline structure was investigated with X-ray diffraction measurements (XRD). The preliminary magnetic and transport measurements evidence the promising properties of this deposition process to provide spinfiltering materials.The authors acknowledge Regione Toscana POR CreO FESR 2014-2020 – azione 1.1.5 sub-azione A1 – Bando 1 “Progetti Strategici di ricerca e sviluppo” which made possible the project “RAM-PVD” (CUP 3647.04032020.157000057_1225).

Interplay of structural chirality, electron spin and topological orbital in chiral molecular spin valves

Chirality has been a property of central importance in physics, chemistry and biology for more than a century. Recently, electrons were found to become spin polarized after transmitting through chiral molecules, crystals, and their hybrids. This phenomenon, called chirality-induced spin selectivity (CISS), presents broad application potentials and far-reaching fundamental implications involving intricate interplays among structural chirality, topological states, and electronic spin and orbitals. However, the microscopic picture of how chiral geometry influences electronic spin remains elusive, given the negligible spin-orbit coupling (SOC) in organic molecules. In this work, we address this issue via a direct comparison of magnetoconductance (MC) measurements on magnetic semiconductor-based chiral molecular spin valves with normal metal electrodes of contrasting SOC strengths. The experiment reveals that a heavy-metal electrode provides SOC to convert the orbital polarization induced by the chiral molecular structure to spin polarization. Our results illustrate the essential role of SOC in the metal electrode for the CISS spin valve effect. A tunneling model with a magnetochiral modulation of the potential barrier is shown to quantitatively account for the unusual transport behavior.

P-orbital half-metallicity in metal-free AsN2 monolayer with robust ferromagnetism

Two-dimensional (2D) metal-free half-metals, the embodiment of abundance ability and intrinsic completely spin-polarization, have attracted increasing interest in the fields of both scientific and technological aspects recently. Based on first-principles, we demonstrate that the metal-free honeycomb lattice of stoichiometry AsN2 exhibits unique electronic structure that results in the complete polarization of p-orbitals at the Fermi level, leading to intrinsic half-metallic behavior. In addition, the AsN2-based spin valve is evaluated by quantum transport simulations, which shows 100% magnetoresistance. Moreover, we find that this ferromagnetism is robust against various perturbations, including strain, carrier doping, electric field, and substrate. These findings provide important foundation for the future spintronics investigations and applications.

Vortex dynamics in a spin valve nanopillar having hybrid polarizer and magnetostatic coupling

This study investigates the observation and control of vortex gyration in the free layer by utilizing polarized current. Modifying the current alone proves challenging in adjusting the frequency and amplitude, as the orbit radius of the vortex core remains constant. To address this, a spin valve nanopillar model with hybrid polarizer is introduced and analyzed, enabling support and gyration of the vortex core in the nanodisk under spin polarized current. Manipulating current density and fine-tuning of hybrid polarizer parameters adjusts system frequency and amplitude. However, with hybrid polarizer, while vortex gyration and higher-frequency signal production increase at higher current densities, the amplitude generally decreases. To mitigate this behavior, the study explores the vortex interactions influenced by magnetostatic coupling in the free layers of spin valve nanopillar. The objective of this paper is to advance the understanding of vortex physics for applications that require greater amplitude microwave signals.

Critical Current Decay in Josephson Junctions Containing Antiferromagnetic NiMn

Josephson junctions containing magnetic materials may be useful in superconducting electronics and memory. One design for a memory cell uses a junction containing an S/F/F'/S spin valve where the two ferromagnetic layers (F, F') have different switching fields. Such a spin valve can be made more robust if the hard layer is pinned by exchange bias with an adjacent antiferromagnetic (AF) layer. We report on the magnetic characterization of NiFe/NiMn and Ni/NiMn bilayer sheet films to confirm the pinning behavior of Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">41</sub> Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">59</sub> . We then report on the fabrication and measurement of S/N/AF/N/S Josephson junctions where NiMn is used as the AF layer, Nb as the S layer, and Cu as the N layer. From measurement of critical current in samples with NiMn thicknesses in the range from 1.2 nm to 6.0 nm, we measure the characteristic supercurrent decay length within NiMn to be 1.0 nm.

Spin diode and spin valve based on an interacting quantum dot coupled with nonmagnetic electrodes

How to control the charge and spin in nanodevices is an important topic in spintronics. In this letter, we theoretically propose a spin diode and spin valve (SV) device controlled by all-electrical means, which is composed of a quantum dot (QD) coupled to a pair of nonmagnetic electrodes. When both electric charge bias and spin bias exist within the device, the I–V curves of this device exhibit an asymmetric distribution, and this asymmetry can be manipulated by the gate voltage. More interestingly, if we apply an external magnetic field on the QD, we can observe significant high- and low-resistance state switching with respect to the magnetic field, which can function as a SV device. This device scheme can be compatible with current technologies and has potential applications in spintronics or quantum processing.

Polyvinylidene Fluoride as an advanced polymer for multifunctional applications- a review

With the advancement of technological development, polymers are grabbing huge consideration in developing Energy Harvesting and Electromechanical devices. Polyvinylidene Fluoride, commonly referred to as PVDF, a semicrystalline polymer from the fluoropolymer family, has received tremendous interest among the research community. This polymer is astonishing to researchers with its excellent piezoelectric and dielectric properties. Apart from this, properties like outstanding thermal stability, flexible processing, anticorrosive, and mechanical strength make them more appropriate for applications such as wearable sensors, nanogenerators, spin valve ultrafiltration membranes, and separators in lithium-ion batteries. Furthermore, while exploring deep through its electrical properties, PVDF is a ferroelectric non-polar insulating matrix and is majorly adopted in insulating materials. But few researchers have resulted that incorporating certain fillers into PVDF can improve their electroactive crystalline phase without an external poling process. This enhancement enhances their piezoelectric properties and makes them an advanced polymer for multifunctional applications such as shielding material for Electromagnetic Interference (EMI), Acoustic sensors, energy storage and smart scaffolds. Hence this review discusses PVDF as an advanced polymer for Multifunctional applications.

Observation of High Magnetic Bistability in Lanthanide (Ln = Gd, Tb and Dy)-Grafted Carbon Nanotube Hybrid Molecular System.

There is an immense research interest in molecular hybrid materials posing novel magnetic properties for usage in spintronic devices and quantum technological applications. Although grafting magnetic molecules onto carbon nanotubes (CNTs) is nontrivial, there is a need to explore their single molecule magnetic (SMM) properties post-grafting to a greater degree. Here, we report a one-step chemical approach for lanthanide-EDTA (Ln = GdIII, 1; TbIII, 2 and DyIII, 3) chelate synthesis and their effective grafting onto MWCNT surfaces with high magnetic bistability retention. The magnetic anisotropy of an Ln-CNT hybrid molecular system by replacing the central ions in the hybrid complex was studied and it was found that system 1 exhibited a magnetization reversal from positive to negative values at 70 K with quasi-anti-ferromagnetic ordering, 2 showed diamagnetism to quasi-ferromagnetism and 3 displayed anti-ferromagnetic ordering as the temperature was lowered at an applied field of 200 Oe. A further analysis of magnetization (M) vs. field (H) revealed 1 displaying superparamagnetic behavior, and 2 and 3 displaying smooth hysteresis loops with zero-field slow magnetic relaxation. The present work highlights the importance of the selection of lanthanide ions in designing SMM-CNT hybrid molecular systems with multi-functionalities for building spin valves, molecular transistors, switches, etc.

Spin injection into heavily-doped n-GaN via Schottky barrier

Spin injection and detection in bulk GaN were investigated by performing magnetotransport measurements at low temperatures. A non-local four-terminal lateral spin valve device was fabricated with Co/GaN Schottky contacts. The spin injection efficiency of 21% was achieved at 1.7 K. It was confirmed that the thin Schottky barrier formed between the heavily n-doped GaN and Co was conducive to the direct spin tunneling, by reducing the spin scattering relaxation through the interface states.