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Engineering of interfacial magnetic properties provides an extra edge in designing heterostructures with desired properties for spintronics and spincaloritronics, without drastically changing the structure of the neighboring nonmagnetic material. Here, we report on the surface termination-enhanced magnetic properties of the ferrimagnetic insulator (FMI) nickel ferrite (NFO) with the inclusion of graphene (Gr) and monolayer hexagonal boron nitride (hBN). Depth-dependent X-ray photoelectron spectroscopy (XPS) measurements reveal the presence of a layer of adsorbed oxygen at the NFO/Gr and NFO/hBN interfaces. Magnetometry and transverse susceptibility measurements indicate that the inclusion of monolayer Gr increases the saturation magnetization (Ms) by 40% and decreases the effective magnetic anisotropy by 50% across 5 K ≤ T ≤ 300 K. A similar but less pronounced effect is observed for the inclusion of hBN. Density functional theory calculations further indicate that the increase in MS due to the inclusion of Gr or hBN arises on oxygen-terminated NFO, as observed in XPS measurements. These results present ways for engineering strong interfacial magnetic effects in FMI/2D nanomaterial systems, controlling magnetism by surface termination, and developing advanced spinterfaces for applications in spincaloritronics and spin insulatronics. [ABSTRACT FROM AUTHOR]

Here, we explore the change in effective magnetic anisotropy of the ferrimagnetic (FM) insulator nickel ferrite (NFO) thin film due to the inclusion of monolayer graphene (MLG) grown on top of the NFO layer. This was done by performing radio frequency (RF) transverse susceptibility (TS) measurements on bare NFO and NFO/MLG bilayer samples for both in-plane (IP) and out-of-plane (OOP) configurations utilizing a tunnel diode oscillator technique. Our magnetometry measurements indicated an enhancement in the overall saturation magnetization of the NFO/MLG bilayer with respect to the bare NFO film. The TS measurements reveal that the inclusion of MLG reduces the effective magnetic anisotropy for both IP and OOP configurations drastically, by up to a factor of 2 over the temperature range 40 K ≤ T ≤ 280 K. Since NFO is a magnetic substrate, it is possible that NFO could induce magnetic ordering in MLG at the NFO/MLG interface via the magnetic proximity effect. Furthermore, since NFO is insulating and MLG is a semimetal, there likely exists a large conductivity difference at the interface, making charge transfer plausible. These two effects could modify the interfacial magnetism leading to a change in the effective magnetic anisotropy. These results highlight the importance of understanding the interfacial magnetism of FM/MLG heterostructures. [ABSTRACT FROM AUTHOR]

Magnetic phase control and room temperature magnetic stability in two-dimensional (2D) materials are indispensable for realising advanced spintronic and magneto-electronic functions. Our current work employs first-principles calculations to comprehensively study the magnetic behaviour of 2D CrOCl, uncovering the impact of strain and electric field on the material. Our studies have revealed that uniaxial strain leads to the feasibility of room temperature ferromagnetism in the layer and also detected the occurrence of a ferromagnetic → antiferromagnetic phase transition in the system, which is anisotropic along the armchair and zigzag directions. Beyond such a strain effect, the coupling of strain and electric field leads to a remarkable enhancement of the Curie temperature (Tc) ∼ 450 K in CrOCl. These predictions based on our detailed simulations show the prospect of multi-stimuli magnetic phase control, which could have great significance for realizing magneto-mechanical sensors. [ABSTRACT FROM AUTHOR]

Phosphorene has a unique set of characteristics such as a semiconducting nature, good carrier mobility and low-spin orbit coupling aspects which makes it a highly prospective two dimensional material for cross-hybrid architectures in nanoelectronics, spintronics, and optoelectronics. In the spintronic context, the creation of a stable magnetic order in phosphorene can be immensely beneficial for designing phosphorene spin circuits. In this work, we present high efficiency spin filtering behaviour in magnetically rendered phosphorene. First, we calculate the effect of doping various 3d block elements in phosphorene to introduce a stable magnetic order. Next, by varying doping concentrations in distinct doping configurations, an extensive phase diagram has been obtained depicting the presence of various electronic and magnetic states. This allows us to achieve a high magnetisation in the presence of various transition metal atoms, with a spin polarisation of ∼100% in half-metallic regimes. The transport behaviour reveals a map of the spin injection efficiency showing enhancement with doping concentration and reaching a perfect spin filtering capacity of ∼100% in the presence of Ti, Cr, Mn, Co, and Fe atoms. The present results offer new insights into engineered designs of multi-functional phosphorene spintronic circuits. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials have brought fresh prospects for spintronics, as evidenced by the rapid scientific progress made in this frontier over the past decade. In particular, for charge perpendicular to plane vertical magnetic tunnel junctions, the 2D crystals present exclusive features such as atomic-level thickness control, near-perfect crystallography without dangling bonds, and novel electronic structure-guided interfaces with tunable hybridization and proximity effects, which lead to an entirely new group of spinterfaces. Such crystals also present new ways of integration of atomically thin barriers in magnetic tunnel junctions and an unprecedented means for developing composite barriers with atomic precision. All these new aspects have sparked interest for theoretical and experimental efforts, revealing intriguing spin-dependent transport and spin inversion effects. Here, we discuss some of the distinctive effects observed in ferromagnetic junctions with prominent 2D crystals such as graphene, hexagonal boron nitride, and transition metal dichalcogenides and how spinterface phenomena at such junctions affect the observed magnetoresistance in devices. Finally, we discuss how the recently emerged 2D ferromagnets bring upon an entirely novel category of van der Waals interfaces for efficient spin transmission and dynamic control through exotic heterostructures. [ABSTRACT FROM AUTHOR]

Phosphorene is a unique two-dimensional semiconductor that exhibits huge potential for nanoelectronic, optoelectronic and spintronic applications and their cross-hybrid electronics. In particular, creation of magnetic phases in phosphorene selectively can provide a multitude of opportunities for developments in 2D spintronic circuits. Doping phosphorene with transition metal atoms can induce sustainable magnetic ordering, making it a diluted magnetic system, however, the viability of high temperature magnetic phases and potential control remain unanswered. In this work, using first-principles calculations, we uncover the impact of doping phosphorene with various 3d block elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) in increasing order of atomic number at various levels of doping. Such an extensive study helps us to find the doping conditions that lead to remarkable feasibility of ferromagnetism and antiferromagnetism up to a strikingly large temperature ∼1150 K, evaluated by mean field theory. The doping concentration and atom type can be used to systematically tune the phases from ferromagnetic and antiferromagnetic to non-magnetic ground states. Our work provides new guidelines for engineering multi-functional spintronic components using phosphorene as a base material for all-phosphorene spintronics. [ABSTRACT FROM AUTHOR]

We report on properties of BaTiO3 thin films where the bandgap is tuned via aliovalent doping of Mn and Nb ions co-doped at the Ti site. The doped films show single-phase tetragonal structure, growing epitaxially with a smooth interface to the substrate. Using piezoforce microscopy, we find that both doped and undoped films exhibit good ferroelectric response. The piezoelectric domain switching in the films was confirmed by measuring local hysteresis of the polarization at several different areas across the thin films, demonstrating a switchable ferroelectric state. The doping of the BaTiO3 also reduces the bandgap of the material from 3.2 eV for BaTiO3 to nearly 2.7 eV for the 7.5% doped sample, suggesting the viability of the films for effective light harvesting in the visible spectrum. The results demonstrate co-doping as an effective strategy for bandgap engineering and a guide for the realization of visible-light applications using its ferroelectric properties. [ABSTRACT FROM AUTHOR]

Phosphorene is a single elemental, two-dimensional semiconductor that has quickly emerged as a high mobility material for transistors and optoelectronic devices. In addition, being a 2D material it can sustain high levels of strain, enabling sensitive modification of its electronic properties. In this paper, we investigate the strain dependent electronic properties of phosphorene nanocrystals. By performing extensive calculations we determine the electrical conductance as a function of uniaxial, as well as biaxial strain stimuli and uncover a unique zone phase diagram. This enables us to uncover conductance oscillations in pristine phosphorene for the first time, by the simple application of strain. We show that such unconventional current–voltage behaviour is tuneable by the nature of strain, and that an additional gate voltage can modulate the amplitude (peak to valley ratio) of the observed phenomena and its switching efficiency. Furthermore, we show that the switching is highly robust against doping and defects. Our detailed results present new leads for innovation in strain based gauging and high-frequency nanoelectronic switches of phosphorene. [ABSTRACT FROM AUTHOR]

Nanolayer black phosphorus (BP) is a direct bandgap semiconducting two dimensional crystal, showing immense promise for future nanoelectronic devices. Here, we report the effect of high-k dielectric and ionic-liquid gate in BP field effect transistors (BP FET). An ambipolar behavior is observed in pristine BP FETs with current modulation of 104. With a high-k HfO2 encapsulation, we observed identical switching performance in the BP FETs, however, with noticeable enhancement in mobility at room temperature. In comparison to the pristine device, the HfO2 encapsulation showed a contrasting decrease in mobility at lower temperatures. BP FETs with electric double layer ionic liquid gate showed a drastic improvement in the subthreshold swing (SS) to 173 mV/dec and operation voltages less than 0.5V in comparison to solid state SiO2 back gated devices. Our results elucidate the effect of different electrostatic conditions on BP transistor channels and open up ways for further exploration of their prospects for nanoelectronic devices and circuits. [ABSTRACT FROM AUTHOR]

Thin films of poly(2,5-bis(3-dodecyl-2-yl)-thieno[3,2-b]thiophene) (C12-PBTTT) polymer under electrolyte gating and doping are investigated as model systems for organic thin films devices approaching the metallic side of a metal-insulator (M-I) transition. For the most doped samples, with an estimated density reaching 8 x 1020 cm-3 holes and a conductivity exceeding 1000 S cm-1, a positive high-field magnetoconductance is found in a limited temperature range window and only when the field is perpendicular to the sample plane. This signature of weak localization, combined with indications of finite zero-temperature conductivity, allows us to identify delocalized metalliclike transport in these thin films, even though the conductivity decreases when cooling down the samples. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (h-BN) is a large bandgap insulating isomorph of graphene, ideal for atomically thin tunnel barrier applications. In this letter, we demonstrate large area chemical vapor deposited (CVD) h-BN as a promising spin tunnel barrier in graphene spin transport devices. In such structures, the ferromagnetic tunnel contacts with h-BN barrier are found to show robust tunneling characteristics over a large scale with resistances in the favorable range for efficient spin injection into graphene. The non-local spin transport and precession experiments reveal spin lifetime ≈500 ps and spin diffusion length ≈1.6 μm in graphene with tunnel spin polarization ≈11% at 100 K. The electrical and spin transport measurements at different injection bias current and gate voltages confirm tunnel spin injection through h-BN barrier. These results open up possibilities for implementation of large area CVD h-BN in spintronic technologies. [ABSTRACT FROM AUTHOR]

We have studied the temperature-dependent (3-300 K) electrical resistance of metal nanowires and nanotubes of the same diameter with the specific aim to understand the changes in electrical transport brought about by a change in the geometry of a nanowire to a nanotube. Single crystalline nanowires and nanotubes of copper were synthesized by electrodeposition in nanoporous alumina templates. The temperature-dependent resistivity data have been analysed using the Bloch-Grüneisen function for the lattice contribution to resistivity, and the characteristic Debye temperature θR was determined along with the residual resistivity ρ0. Substantial size effects were observed in both the parameters ρ0 and θR, where the former is enhanced and the latter is suppressed from bulk to nanowires and further to nanotubes. It has been observed that the transport parameters in the nanotubes with wall thickness t are similar to those of a nanowire with diameter d, where d ≈ 2t in the specific size range used in this work. It is suggested that appreciable size effects in the electrical transport parameters occur due to the extra surface in the nanotube. In both nanotubes and nanowires, the single parameter that determines the size effect is the surface area to volume ratio. [ABSTRACT FROM AUTHOR]

We report a comprehensive study of the electrical and magnetotransport properties of nanocrystals of La0.67Ca0.33MnO3 (LCMO) (with size down to 15 nm) and La0.5Sr0.5CoO3 (LSCO) (with size down to 35 nm) in the temperature range 0.3-5K and magnetic fields up to 14 T. The transport, magneto-transport and nonlinear conduction (I -V curves) were analysed using the concept of spin-polarized tunnelling in the presence of Coulomb blockade. The activation energy of transport, Δ, was used to estimate the tunnelling distances and the inverse decay length of the tunnelling wave function (χ) and the height of the tunnelling barrier (ΦB). The magneto-transport data were used to find the magnetic field dependences of these tunnelling parameters. The data taken over a large magnetic field range allowed us to separate out the magnetoresistance (MR) contributions at low temperatures arising from tunnelling into two distinct contributions. In LCMO, at low magnetic field, the transport and MR are dominated by the spin polarization, while at higher magnetic field the MR arises from the lowering of the tunnel barrier by the magnetic field, leading to an MR that does not saturate even at 14 T. In contrast, in LSCO, which does not have substantial spin polarization, the first contribution at low field is absent, while the second contribution related to barrier height persists. The idea of intergrain tunnelling has been validated by direct measurements of the nonlinear I -V data in this temperature range, and the I -V data were found to be strongly dependent on magnetic field. We made the important observation that a gaplike feature (with magnitude ∼EC, the Coulomb charging energy) shows up in the conductance g(V) at low bias for the systems with the smallest nanocrystal size at the lowest temperatures (T ⩽ 0.7 K). The gap closes when the magnetic field and temperature are increased. [ABSTRACT FROM AUTHOR]

We have measured the electrical resistivity of a single strand of a ferromagnetic Ni nanowire of diameter 55 nm using a four-probe method in the temperature range 3–300 K. The wire used is chemically pure and is a high quality oriented single crystalline sample in which the temperature independent residual resistivity is determined predominantly by surface scattering. Precise evaluation of the temperature dependent resistivity (ρ) allowed us to identify quantitatively the electron-phonon contribution (characterized by a Debye temperature θR) as well as the spin-wave contribution, which is significantly suppressed upon size reduction. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) semiconducting dichalcogenides hold exceptional promise for next-generation electronic and photonic devices. Despite this potential, the pervasive presence of defects in 2D dichalcogenides results in carrier mobility and photoluminescence (PL) that fall significantly short of theoretical predictions. Although defect passivation offers a potential solution, its effects have been inconsistent. This arises from the lack of chemical understanding of the surface chemistry of the 2D material. In this work, we uncover new binding chemistry using a sequence-specific chemical passivation (SSCP) protocol based on 2-furanmethanothiol (FSH) and bis(trifluoromethane) sulfonimide lithium salt (Li-TFSI), which demonstrates a synchronized 100-fold enhancement in both carrier mobility and PL in WS 2 monolayers. We propose an atomic-level synergistic defect passivation mechanism of both neutral and charged sulfur vacancies (SVs), supported by ultrafast transient absorption spectroscopy (TA), Hard X-ray photoelectron spectroscopy (HAXPES), and density functional theory (DFT) calculations. Our results establish a new semiconductor quality benchmark for 2D WS 2 , paving the way for the development of sustainable 2D semiconductor technologies.

Two-dimensional (2D) van der Waals heterostructures combine the distinct properties of individual 2D materials, resulting in metamaterials, ideal for emergent electronic, optoelectronic, and spintronic phenomena. A significant challenge in harnessing these properties for future hybrid circuits is their large-scale realization and integration into graphene interconnects. In this work, we demonstrate the direct growth of molybdenum disulfide (MoS 2 ) crystals on patterned graphene channels. By enhancing control over vapor transport through a confined space chemical vapor deposition growth technique, we achieve the preferential deposition of monolayer MoS 2 crystals on monolayer graphene. Atomic resolution scanning transmission electron microscopy reveals the high structural integrity of the heterostructures. Through in-depth spectroscopic characterization, we unveil charge transfer in Graphene/MoS 2 , with MoS 2 introducing p-type doping to graphene, as confirmed by our electrical measurements. Photoconductivity characterization shows that photoactive regions can be locally created in graphene channels covered by MoS 2 layers. Time-resolved ultrafast transient absorption (TA) spectroscopy reveals accelerated charge decay kinetics in Graphene/MoS 2 heterostructures compared to standalone MoS 2 and upconversion for below band gap excitation conditions. Our proof-of-concept results pave the way for the direct growth of van der Waals heterostructure circuits with significant implications for ultrafast photoactive nanoelectronics and optospintronic applications.

Innovations in resistive switching devices constitute a core objective for the development of ultralow-power computing devices. Forming-free resistive switching is a type of resistive switching that eliminates the need for an initial high voltage for the formation of conductive filaments and offers promising opportunities to overcome the limitations of traditional resistive switching devices. Here, we demonstrate mixed charge state oxygen vacancy-engineered electroforming-free resistive switching in NiFe 2 O 4 (NFO) thin films, fabricated as asymmetric Ti/NFO/Pt heterostructures, for the first time. Using pulsed laser deposition in a controlled oxygen atmosphere, we tune the oxygen vacancies together with the cationic valence state in the nickel ferrite phase, with the latter directly affecting the charge state of the oxygen vacancies. The structural integrity and chemical composition of the films are confirmed by X-ray diffraction and hard X-ray photoelectron spectroscopy, respectively. Electrical transport studies reveal that resistive switching characteristics in the films can be significantly altered by tuning the amount and charge state of the oxygen vacancy concentration during the deposition of the films. The resistive switching mechanism is seen to depend upon the migration of both singly and doubly charged oxygen vacancies formed as a result of changes in the nickel valence state and the consequent formation/rupture of conducting filaments in the switching layer. This is supported by the existence of an optimum oxygen vacancy concentration for efficient low-voltage resistive switching, below or above which the switching process is inhibited. Along with the filamentary switching mechanism, the Ti top electrode also enhances the resistive switching performance due to interfacial effects. Time-resolved measurements on the devices display both long- and short-term potentiation in the optimized vacancy-engineered NFO resistive switches, ideal for solid-state synapses achieved in a single system. Our work on correlated oxide forming-free resistive switches holds significant potential for CMOS-compatible low-power, nonvolatile resistive memory and neuromorphic circuits.

Adherence of metal oxides to graphene is of fundamental significance to graphene nanoelectronic and spintronic interfaces. Titanium oxide and aluminum oxide are two widely used tunnel barriers in such devices, which offer optimum interface resistance and distinct interface conditions that govern transport parameters and device performance. Here, we reveal a fundamental difference in how these metal oxides interface with graphene through electrical transport measurements and Raman and photoelectron spectroscopies, combined with ab initio electronic structure calculations of such interfaces. While both oxide layers cause surface charge transfer induced p-type doping in graphene, in sharp contrast to TiO x , the AlO x /graphene interface shows the presence of appreciable sp 3 defects. Electronic structure calculations disclose that significant p-type doping occurs due to a combination of sp 3 bonds formed between C and O atoms at the interface and possible slightly off-stoichiometric defects of the aluminum oxide layer. Furthermore, the sp 3 hybridization at the AlO x /graphene interface leads to distinct magnetic moments of unsaturated bonds, which not only explicates the widely observed low spin-lifetimes in AlO x barrier graphene spintronic devices but also suggests possibilities for new hybrid resistive switching and spin valves.

Emergent technologies are required in the field of nanoelectronics for improved contacts and interconnects at nano and micro-scale. In this work, we report a highly-efficient nanolithography process for the growth of cobalt nanostructures requiring an ultra-low charge dose (15 μC cm -2 , unprecedented in single-step charge-based nanopatterning). This resist-free process consists in the condensation of a ∼28 nm-thick Co 2 (CO) 8 layer on a substrate held at -100 °C, its irradiation with a Ga + focused ion beam, and substrate heating up to room temperature. The resulting cobalt-based deposits exhibit sub-100 nm lateral resolution, display metallic behaviour (room-temperature resistivity of 200 μΩ cm), present ferromagnetic properties (magnetization at room temperature of 400 emu cm -3 ) and can be grown in large areas. To put these results in perspective, similar properties can be achieved by room-temperature focused ion beam induced deposition and the same precursor only if a 2 × 10 3 times higher charge dose is used. We demonstrate the application of such an ultra-fast growth process to directly create electrical contacts onto graphene ribbons, opening the route for a broad application of this technology to any 2D material. In addition, the application of these cryo-deposits for hard masking is demonstrated, confirming its structural functionality., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The two-dimensional (2D) semiconductor molybdenum disulfide (MoS 2 ) has attracted widespread attention for its extraordinary electrical-, optical-, spin-, and valley-related properties. Here, we report on spin-polarized tunneling through chemical vapor deposited multilayer MoS 2 (∼7 nm) at room temperature in a vertically fabricated spin-valve device. A tunnel magnetoresistance (TMR) of 0.5-2% has been observed, corresponding to spin polarization of 5-10% in the measured temperature range of 300-75 K. First-principles calculations for ideal junctions result in a TMR up to 8% and a spin polarization of 26%. The detailed measurements at different temperature, bias voltages, and density functional theory calculations provide information about spin transport mechanisms in vertical multilayer MoS 2 spin-valve devices. These findings form a platform for exploring spin functionalities in 2D semiconductors and understanding the basic phenomena that control their performance.

We investigate if the functionality of spin crossover molecules is preserved when they are assembled into an interfacial device structure. Specifically, we prepare and investigate gold nanoparticle arrays, into which room-temperature spin crossover molecules are introduced, more precisely, [Fe(AcS-BPP)2](ClO4)2, where AcS-BPP = (S)-(4-{[2,6-(dipyrazol-1-yl)pyrid-4-yl]ethynyl}phenyl)ethanethioate (in short, Fe(S-BPP)2). We combine three complementary experiments to characterize the molecule-nanoparticle structure in detail. Temperature-dependent Raman measurements provide direct evidence for a (partial) spin transition in the Fe(S-BPP)2-based arrays. This transition is qualitatively confirmed by magnetization measurements. Finally, charge transport measurements on the Fe(S-BPP)2-gold nanoparticle devices reveal a minimum in device resistance versus temperature, R(T), curves around 260-290 K. This is in contrast to similar networks containing passive molecules only that show monotonically decreasing R(T) characteristics. Backed by density functional theory calculations on single molecular conductance values for both spin states, we propose to relate the resistance minimum in R(T) to a spin transition under the hypothesis that (1) the molecular resistance of the high spin state is larger than that of the low spin state and (2) transport in the array is governed by a percolation model.