Spin Valve Research Articles

A seamless graphene spin valve based on proximity to van der Waals magnet Cr2Ge2Te6

A seamless graphene spin valve based on proximity to van der Waals magnet Cr2Ge2Te6

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.

Spin-Lifetime Probe for Detecting Intramolecular Noncovalent Interaction in Organic Semiconductors.

Intramolecular noncovalent interaction (INCI), a crucial strategy for effectively enhancing molecular planarity and extending π-electron delocalization in organic semiconductors (OSCs), has played an increasingly important role in optoelectronic applications. However, though the INCI formation is regularly considered to improve the device performance by literature, there is no feasible approach to directly and reliably characterizing its formation in practical-OSC films thus far. Here in this study, by theoretical analysis and calculation, the generation of INCIs in OSCs is found, normally consisting of relatively heavy elements, such as O···Se, O···S, N···S interactions, etc., can induce enhanced strength of spin-orbit coupling, the primary factor dominating spin lifetime in OSCs. Based on this newly discovered theory, spin lifetime is creatively employed as a probe for sensitively detecting INCIs in OSC films via spin valves or field-induced electron paramagnetic resonance, respectively. This study will highly promote academic and applicable developments of the cross-cutting frontier research field between organic spintronics and electronics.

Femtosecond-laser-induced reversal in in-plane-magnetized spin valves

Femtosecond-laser-induced reversal in in-plane-magnetized spin valves

Josephson spin valve controlled by a superconducting trigger effect

The supercurrent in a Josephson SF1S1F2sIS spin valve (“S” is for superconductor, “F” is for ferromagnet, and “I” is for insulator) is studied theoretically. It is found that by rotating the magnetization of one of the ferromagnetic layers, a smooth switching of the system between two states with different critical currents is possible. The operating range of the device can be adjusted by varying the thickness of the intermediate s-layer. The proposed structure is a promising scalable control element for the use in superconducting electronics.

Spin valve as THz emitter providing amplitude modulation

Spin valve as THz emitter providing amplitude modulation

Room temperature spin injection study across semi-crystalline PVDF-HFP thin films in PVDF-HFP/NiFe bilayers and Ag/(NiFe or Co)/PVDF-HFP/NiFe spin valves

Spin injection across 160 nm thick semi-crystalline Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) is methodically investigated at room temperature in PVDF-HFP/NiFe bilayers and Ag/(NiFe or Co)/PVDF-HFP/NiFe vertical organic spin valves (OSVs) using both the co-planar waveguide ferromagnetic resonance (CPW-FMR: 7-35 GHz) and magnetoresistance (MR) techniques. The structural and microstructural characteristics of PVDF-HFP reveal the formation of mixed non-ferroelectric alpha and ferroelectric beta phases. The spin injection due to the transfer of angular momentum in PVDF-HFP/NiFe is quantified by measuring the spin-mixing conductance (g↑↓) and the enhancement in Gilbert damping (α) parameters from CPW-FMR data. A significant increase inαof 26% andg↑↓of (2.72 ± 0.45) × 1019m-2highlights the efficient spin injection into the PVDF-HFP spacer layer. Further, the MR in OSV structures reveals a room temperature spin injection with a maximum MR of 0.278 ± 0.006% for Ag/Co/PVDF-HFP/NiFe and 0.349 ± 0.039% for the Ag/NiFe/PVDF-HFP/NiFe devices. Furthermore, the spin injection processes are discussed w.r.t to bias voltages, interfaces and microwave frequencies.

Quantifying spin-torque efficiency and magnetoresistance coefficient by microwave photoresistance in spin-torque ferromagnetic resonance

During the spin-torque ferromagnetic resonance (ST-FMR) measurement, the magnetization precession driven by the microwave field yields the radio frequency (rf) oscillating magnetoresistance and its time-averaged change (photoresistance). Here, we find that the strength of photoresistance can be directly determined by using dc bias current Idc modulating the symmetric component VS of the ST-FMR voltage spectrum. By measuring the angular dependence of photoresistance, we can quantify the in-plane and out-of-plane precession angles of ST-FMR, the actual rf current distribution in the magnetic and non-magnetic sublayers, and the magnitude of spin-torque and various magnetoresistance coefficients. These experimentally obtained values and analysis methods can more accurately quantify the spin-torque efficiency of both in-plane and out-of-plane spin polarizations by self-consistent calculation of the precession angle without harsh assumptions. And, we further confirm this universal method in three spintronic systems: the prototypical Pt/Py bilayer with anisotropic magnetoresistance (AMR), Py/Cu/Co20Tb80 spin valve trilayer with AMR and giant magnetoresistance, and [Co/Ni]3/Co/Pt multilayer with AMR and anisotropic interface magnetoresistance. This method eliminates potential deviation in calculating spin-torque efficiency by previously reported line shape analyzation and linewidth modulation methods of the ST-FMR technique and significantly extends its application range in characterizing spintronic materials and nanodevices.

Impact of orbital hybridization on spin-polarized electronic transport through Ni-MAPbI3 interfaces

The solution-processed methylammonium lead tri-iodine (MAPbI3), with long spin lifetimes and large spin diffusion lengths, has merit for developing stable perovskite spin valves (PeSV) with low saturation fields. By far, it remains challenging to avoid ill-defined ferromagnet-MAPbI3 interfaces during device fabrications using solution methods and to quantify the hybridized interfacial electronic and magnetic structures. Herein, an annealing-free method was developed for the fabrication of MAPbI3 based PeSV. In comparison to a thermally annealed device, an improved room temperature magnetoresistance (MR) was achieved. We found remarkable interfacial contributions to anisotropic magnetoresistance and MR. The first-principles calculation was further adopted to quantify the interfacial spin and orbital moments. Our results suggest that the orbital hybridization and the spin transfer are remarkable for the formation of the spin-dependent interfacial density of states. It consequently affects magnetic switching behaviors. This study holds an exceptionally important role for a deep understanding of the spin-polarized electronic transport through the Ni-MAPbI3 hybridized interface.

Spin valve effect in the van der Waals heterojunction of Fe3GeTe2/tellurene/Fe3GeTe2

Spintronic devices are regarded as prime candidates for addressing the demands of emergent applications such as in-memory computing and the Internet of Things, characterized by requirements for high speed, low energy consumption, and elevated storage density. Among these, spin valves, serving as fundamental structures of magnetic random-access memory, have garnered substantial attention in recent years. This study introduces an all van der Waals (vdW) heterostructure composed of Fe3GeTe2 (FGT)/tellurene/FGT, wherein a thin layer of Weyl semiconductor Te is interposed between two ferromagnetic FGT layers. The proposed configuration exhibits a characteristic spin valve effect at temperatures below 160 K. This effect is attributed to spin-dependent transport and spin-dependent scattering phenomena occurring at the interfaces of the constituent materials. Furthermore, as temperature decreases, the magnetoresistance ratio (MR) of the device increases, indicative of the heightened polarization ratio of FGT, with an MR of 0.43% achievable as the temperature approaches 5 K. This investigation elucidates the underlying operational mechanisms of two-dimensional spin valve devices and lays the groundwork for the realization of spin-based integrated circuits.

Room temperature chiral magnetoresistance in a chiral-perovskite-based perpendicular spin valve

Chirality-induced spin selectivity (CISS) allows for the generation of spin currents without the need for ferromagnets or external magnetic fields, enabling innovative spintronic device designs. One example is a chiral spin valve composed of ferromagnetic and chiral materials, in which the resistance depends on both the magnetization direction of the ferromagnet and the chirality of the chiral material. So far, chiral spin valves have predominately employed chiral organic molecules, which have limited device applications. Chiral perovskites, which combine the properties of inorganic perovskites with chiral organic molecules, provide an excellent platform for exploring CISS-based devices. However, previous chiral perovskite-based spin valves exhibited magnetoresistance (MR) only at low temperatures. Here, we report room temperature MR in a chiral spin valve consisting of chiral perovskites/AlOx/perpendicular ferromagnet structures. It is observed that the chiral MR increases with rising temperature, suggesting the crucial role of phonon-induced enhancement of spin–orbit coupling in CISS in our device. Furthermore, we enhanced the chiral MR by introducing chiral molecules with amplified chirality. This highlights the potential of chirality engineering to improve CISS and the associated chiral MR, thereby opening possibilities for chiral spin valves tailored for cutting-edge spintronic applications.

Oblique spin injection to graphene via geometry controlled magnetic nanowires

We exploit the geometry of magnetic nanowires, which define 1D contacts to an encapsulated graphene channel, to introduce an out-of-plane component in the polarisation of spin carriers. By design, the magnetic nanowires traverse the angled sides of the 2D material heterostructure. Consequently, the easy axis of the nanowires is inclined, and so the local magnetisation is oblique at the injection point. As a result, when performing non-local spin valve measurements we simultaneously observe both switching and spin precession phenomena, implying the spin population possesses both in-plane and out-of-plane polarisation components. By comparing the relative magnitudes of these components, we quantify the angle of the total spin polarisation vector. The extracted angle is consistent with the angle of the nanowire at the graphene interface, evidencing that the effect is a consequence of the device geometry. This simple method of spin-based vector magnetometry provides an alternative technique to define the spin polarisation in 2D spintronic devices.

Charge and Spin Transfer Dynamics in a Weakly Coupled Porphyrin Dimer.

The dynamics of electron and spin transfer in the radical cation and photogenerated triplet states of a tetramethylbiphenyl-linked zinc-porphyrin dimer were investigated, so as to test the relevant parameters for the design of a single-molecule spin valve and the creation of a novel platform for the photogeneration of high-multiplicity spin states. We used a combination of multiple techniques, including variable-temperature continuous wave EPR, pulsed proton electron-nuclear double resonance (ENDOR), transient EPR, and optical spectroscopy. The conclusions are further supported by density functional theory (DFT) calculations and comparison to reference compounds. The low-temperature cw-EPR and room-temperature near-IR spectra of the dimer monocation demonstrate that the radical cation is spatially localized on one side of the dimer at any point in time, not coherently delocalized over both porphyrin units. The EPR spectra at 298 K reveal rapid hopping of the radical spin density between both sites of the dimer via reversible intramolecular electron transfer. The hyperfine interactions are modulated by electron transfer and can be quantified using ENDOR spectroscopy. This allowed simulation of the variable-temperature cw-EPR spectra with a two-site exchange model and provided information on the temperature-dependence of the electron transfer rate. The electron transfer rates range from about 10.0 MHz at 200 K to about 53.9 MHz at 298 K. The activation enthalpies Δ‡H of the electron transfer were determined as Δ‡H = 9.55 kJ mol-1 and Δ‡H = 5.67 kJ mol-1 in a 1:1:1 solvent mixture of CD2Cl2/toluene-d8/THF-d8 and in 2-methyltetrahydrofuran, respectively, consistent with a Robin-Day class II mixed valence compound. These results indicate that the interporphyrin electronic coupling in a tetramethylbiphenyl-linked porphyrin dimer is suitable for the backbone of a single-molecule spin valve. Investigation of the spin density distribution of the photogenerated triplet state of the Zn-porphyrin dimer reveals localization of the triplet spin density on a nanosecond time scale on one-half of the dimer at 20 K in 2-methyltetrahydrofuran and at 250 K in a polyvinylcarbazole film. This establishes the porphyrin dimer as a molecular platform for the formation of a localized, photogenerated triplet state on one porphyrin unit that is coupled to a second redox-active, ground-state porphyrin unit, which can be explored for the formation of high-multiplicity spin states.

Medium dynamic field range linear bipolar spin valve sensor through soft pinning the sensing layer

Magnetic sensor with spin valve-GMR technology with medium dynamic range is designed for a diversity of applications, including linear and rotary position measurements, proximity switches, and current sensors. For this, the sensing layer (SL) of the spin valve stack was modified by a soft pinning layer (SPL) through an exchange bias field created by an antiferromagnetic layer which has a lower blocking temperature than the one that is kept adjacent to the pinned layer. Numerical simulation was carried out to control the bias field by keeping a non-magnetic Ru spacer layer between the SPL and SL layers and the results were experimentally verified. The magnetic sensor was fabricated with linear operating field range of the order ±100 Oe having a sensitivity of the order of 0.1 m V V−1 Oe−1 near zero field. The thermal performance confirms that the device can be operated in the temperature range of −40 ∘C to 125 ∘C and it has a thermal coefficient of voltage around 15 µV V−1∘C−1.

The martensitic structures, exchange bias effect and training effect in Ni-Mn-Ga ribbons

The exchange bias effect is the physical basics of spin valves and magnetic recording devices. A stable exchange bias effect would be suitable for practical application. In this work, Ni50Mn50-xGax (11≤ x ≤16) ribbons were obtained by melt spinning. The grain size and microstructure have been tuned through melt spinning, which changes the exchange interaction in ribbons and thus gets a giant and stable exchange bias effect. As the increase of x, the structure of Ni50Mn50-xGax (11≤ x ≤16) ribbons undergoes a transition from non-modulated martensite to non-modulated martensite &10 layers modulated martensite to 10 layers modulated martensite. The average grain size of all ribbons is less than 10 μm, and the martensitic plate widths are smaller than 200 nm. With the increasing x or the cooling fields, the magnetization of the ribbons has been enhanced. As a result, the competition between ferromagnetic and antiferromagnetic interactions has been changed and thus influencing spin glass behavior. Furthermore, a low degree of attenuation for the exchange bias effect after continuous cycles has been achieved which arises from the stable spin configuration with a larger contribution of frozen spin which has a slow relaxation rate. For example, the exchange bias field of 8.78 kOe in Ni50Mn38Ga12 ribbons can be achieved under the 40 kOe field cooling at 10 K, and the exchange bias field after infinite cycles can be kept at 8.58 kOe, the degree of attenuation is only 3.4 %. This work enriches the research on the exchange bias effect of Heusler alloys and provides the experimental basis and theoretical support for designing a stable exchange bias effect.

High polarization sensitivity passive spin Photogalvanic devices based on 2D perovskite CsMnBr4/CsSbCl3Br/CsMnBr4 heterojunction

In recent years, Dion-Jacobson (D-J) perovskite has been extensively studied. In order to further study the application of D-J perovskite materials in spin-optoelectronic multifunctional devices, this paper is based on CsSbCl3Br and CsMnBr4, a zero-band gap semi-metallic material with the same ferromagnetic ground state and the same crystal structure. In this paper, put forward with transverse CsMnBr4/CsSbCl3Br/CsMnBr4 heterojunction optoelectronic devices. The characteristics of photocurrent are discussed using parallel configuration (PC) and anti-parallel configuration (APC) magnetoelectric poles under two conditions: vertical incidence of linearly polarized light and elliptically polarized light utilizing density functional theory and the non-equilibrium Green’s function method. The results reveal that the device can achieve complete spin polarization photocurrent, pure spin current, perfect spin filtering effect, and excellent spin valve effect, with high extinction ratios. Under linearly polarized light, the maximum extinction ratio reaches 2747 for the PC configuration and 5200 for the APC configuration. For elliptically polarized light, the extinction ratio is 739 for the PC configuration and reaches a maximum of 240 for the APC configuration. These results indicate that the lateral CsMnBr4/CsSbCl3Br/CsMnBr4 heterojunction has broad multi-functional application prospects in the field of optoelectronics and spintronics.

Features of the Behavior of an Fe1/Cu/Fe2/Cu/Pb Superconducting Spin Valve on a Piezoelectric Substrate

Features of the Behavior of an Fe1/Cu/Fe2/Cu/Pb Superconducting Spin Valve on a Piezoelectric Substrate

Current-perpendicular-to-plane transport properties of 2D ferromagnetic material CrTe2

Abstract In recent years, heterostructures of van der Waals (vdW) ferromagnetic materials have become a focal point in the study of low-dimensional spintronic devices. The current direction in spin valves is commonly perpendicular to the plane (CPP). However, the transport properties of the CPP mode remain largely unexplored. In this work, current-in-plane (CIP) mode and CPP mode for CrTe2 thin films have been carefully studied. The temperature-dependent longitudinal resistance transitions from metallic (CIP) to semiconductor behavior (CPP), with the electrical resistivity of CPP increased by five orders of magnitude. More importantly, the transport properties of the CPP can be categorized into a single-gap Tunneling Through model with the activation energy (E a) of ~1.34 meV/gap at 300-150 K, Variable Range Hopping (VRH) model with a linear Negative Magnetic Resistance (NMR) at 150 -20 K, and weak localization (WL) region with a nonlinear MR at below 20 K. This study explores the vertical transport in CrTe2 materials for the first time, contributing to understand its unique properties and pave the way for its potential in spin valve devices.

Different exchange bias behavior caused by tuning glassy state in Ni50Mn37Ga13 ribbons

Exchange bias plays a significant role in the application of spin valves and magnetic sensors. A spontaneous exchange bias field of 0.75 kOe can be observed in the annealed Ni50Mn37Ga13 ribbons, while a giant exchange bias field of 6.14 kOe occurs in the quenched samples under field cooling. This is due to the different lattice parameters and microscopic morphology making the annealed and quenched samples, respectively, form superspin glass and spin glass embedded in the antiferromagnetic matrix. The conditions for superspin glass and spin glass to overcome the energy barrier of spin reconfiguration are different, resulting in the difference in exchange bias behavior. This work combines the magnetic properties with the crystal structure and microscopic morphology, providing a method of controlling the glassy state by heat treatments to regulate the exchange bias of Heusler alloys.

Intrinsic spin transport properties observed in contamination-free graphene-based spin valve

Graphene-based spintronics has attracted great interest while the spin transport and relaxation in clean graphene at low temperatures are still unrevealed. Here, we present an all-dry van der Waals transfer technique to fabricate contamination-free single-layer graphene based lateral spin valve devices. We have obtained a non-local resistance as large as 125 Ω and a spin lifetime of up to 2.47 ns at room temperature simultaneously. Strikingly, an unexpected temperature dependence of spin transport has been observed, where the spin lifetime τ and the spin diffusion length λ decrease with decreasing temperatures below 150 K (τmin = 2 ns, λmin = 10.7 μm at 1.5 K and τmax = 4.63 ns, λmax = 14.5 μm at 150 K). By measuring the oblique Hanle spin precession, we find that the spin-lifetime anisotropy of our device is more pronounced out-of-plane at 75 K. This suggests that the spin relaxation in clean graphene is more effected by the out-of-plane spin orbit field or gauge fields at low temperatures. Our results provide new insight into the fundamental spin transport of graphene, paving a way for their practical applications in spintronics.