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The spin-transfer torque magnetic tunneling junction (MTJ) technology may pave a way to a universal memory paradigm. MTJ devices with perpendicular magnetic anisotropy have the potential to have high thermal stability, high tunneling magnetoresistance, and low critical current for energy-efficient current-induced magnetization switching. Using devices fabricated through focused ion beam etching with Ga-and Ne-ion beams, this paper aimed to understand the size dependence of the current/voltage characteristics in the sub-10 nm range. The switching current density drastically dropped around 1 MA/cm2 as the device size was reduced below 10 nm. A stability of over 22 kT measured for a 5 nm device indicated a significantly reduced spin relaxation time.

We have examined a dynamical spin injection in a CoFeB/Pt/CoFeB trilayered structure. Although the contribution of the spin pumping was eliminated by the symmetric spin injection from the upper and lower CoFeB layers, a clear voltage change due to the inverse spin Hall effect has been observed. We find that the observed signal can be quantitatively explained by considering the thermal spin injection due to the heating effect during ferromagnetic resonance (FMR). This innovative demonstration indicates the significant contribution of FMR heating in the dynamical spin injection. [ABSTRACT FROM AUTHOR]

We present the fabrication and characterization of an array of microbridge-structured magnetoelectric (ME) thin film sensors which are constructed by an ME composite consisting of a 1 $\mu \text{m}$ PZT film and a 1 $\mu \text{m}$ amorphous FeCoSiB film deposited on a partially thinned Si substrate. Characterization of the sensor showed a large ME coefficient of $16.87~\text {V/cm}\cdot \text {Oe}$ in resonance at 7.9 kHz without a charge amplifier. The sensitivity was enhanced by 1.65 times when three identical sensors were connected in series. The resonant frequency of the sensor was precisely regulated by adjusting the etched area of the substrate, and the 3 dB bandwidth of the resonant frequency was doubled after two adjusted sensors were connected in parallel. [ABSTRACT FROM AUTHOR]

The effects of the partial substitution of Mn by Co/Fe on the structural, magnetostatic, and magnetodynamic properties of Ni–Mn–In Heusler alloy films were studied using X-ray diffraction, field-dependent magnetization, and ferromagnetic resonance studies. It was observed that the substitution of up to 3 at.% Co or Fe atoms in Mn sites does not alter the crystal structure much. However, an increase in grain size and surface roughness was noticed upon substitution of the fourth element. The magnetic moment of the films could be increased up to 120 kA/m by introducing Co/Fe in Mn sites. For the first time, low Gilbert damping constant ($\alpha$) of 0.008 is observed in Co substituted Ni–Mn–In film together with high saturation magnetization, high perpendicular anisotropy, and an easy axis along film plane, which are the promising factors for application in high-density random-access memory devices. [ABSTRACT FROM AUTHOR]

The electronic structures of chromium dioxide (CrO2) with different concentrations and distributions of oxygen vacancy were investigated by first-principle calculations based on density functional theory. It was found that even at fairly high vacancy concentration, the half metallicity of CrO2 keeps intact as long as oxygen vacancies do not pair in the same octahedron; when two vacancies appear in one octahedron, the half metallic nature of CrO2 may be severely weakened or completely destroyed even at much lower vacancy concentration depending on the vacancy-pair configuration. Our results suggest that the half metallicity of CrO2 is more sensitive to the relative positions of oxygen vacancies than to the vacancy concentration. By investigating the position dependence of the formation energy, the formation and the spreading mode of oxygen vacancies were discussed. The results show that once an oxygen vacancy forms, the next oxygen vacancy tends to appear in the equatorial plane of the same octahedron to reduce Cr4+ to Cr3+. This kind of pairing nature indicates that the oxygen vacancies may tend to spread in a planar mode along the [00l] direction. [ABSTRACT FROM AUTHOR]

We investigated the influence of thermal deformation on the magnetic properties of flexible FeGa/IrMn exchange-biased (EB) bilayers grown on polyvinylidene fluoride (PVDF) membranes with the pinning direction parallel to the thermal deformation directions \alpha 31 and \alpha 32 of PVDF. Because with increasing temperature, the uniaxial anisotropy is reoriented from the \alpha 32 to \alpha 31 directions by the thermally induced compressive strain along the \alpha 32 direction, both the coercive field Hc and the loop squareness Mr/Ms of FeGa/IrMn bilayers display a complex temperature-dependent behavior. The EB field Hc decreases with increasing temperature. A modified Stoner–Wohlfarth model was employed to account for the temperature dependence of magnetic properties in the flexible FeGa/IrMn bilayers. [ABSTRACT FROM PUBLISHER]

The conventional CMOS transistors reach its power wall due to the increasing leakage current as technology scales down. The spintronic devices show a great promise as one of the alternatives to replace CMOS technology for the next-generation low-power integrated circuits. Recently, the spintronic memory, e.g., spin-transfer torque magnetic random-access memory, has been successfully commercialized. However, the spintronic logic circuits face critical problems and challenges, such as poor direct cascading ability and small operation gain, before practical applications. In this paper, we propose a complementary spintronic logic (CSL) family based on a novel four-terminal spin Hall effect-driven magnetic tunnel junction (FT-SHE-MTJ). Fully electrically separated write/read paths of the proposed FT-SHE-MTJ device can overcome the challenges of direct cascading and operation gain in current spintronic logic circuits. With the aid of a compact model, the functionality and the performance of the proposed CSL circuits are evaluated. Simulation results show that the correct logic fan-out operation can be achieved with a voltage below 150 mV, which is promising for low-power computing. [ABSTRACT FROM AUTHOR]

The dynamics of magnetic vortex in nanodisks with a ring-shaped magnetic defect is investigated using micromagnetic simulations. It is found that a spin-polarized current can drive the vortex core precession, and the presence of the ring affects the final steady oscillation radius Rv and the precession frequency $f$ of the vortex core. Moreover, the precession frequency of the vortex core is sensitive to the size of the ring. In addition, compared with regular nanodisks, the oscillation frequency can be modulated in a wide range for a small exchange stiffness constant A_{r} of the ring. The ring-shaped defect paves a new pathway for regulating the frequency of magnetic vortex oscillators. [ABSTRACT FROM AUTHOR]

We prepared CH3NH3PbI3-coated La0.67Sr0.33MnO3 (LSMO) granular composites. Significant magnetoresistance (MR) effect has been observed. The resistivity of CH3NH3PbI3-coated LSMO is more than five orders larger than that of LSMO. The MR effect from LSMO bulk can be safely excluded. The MR curves can be separated into two parts: 1) low-field MR (LFMR) and 2) high-field MR (HFMR). LFMR can be attributed to the spin retaining transport in CH3NH3PbI3 and spin-dependent scattering at the LSMO particle surface, and the HFMR can be explained by the field-dependent carrier injection at the interface of LSMO and CH3NH3PbI3. The observation of MR in CH3NH3PbI3-coated LSMO granular composites demonstrates the potential application of organolead trihalide perovskite as spin transporting medium in organic spintronics. [ABSTRACT FROM AUTHOR]

Control of the magnetic anisotropy under different strain states is important for the manipulation of magnetization in flexible spintronic devices. Here, the electric field control of magnetic anisotropy was investigated in flexible Fe81Ga19(FeGa)/polyvinylidene fluoride multiferroic heterostructures under different compressive strains. The initial uniaxial magnetic anisotropy is enhanced with increasing the compressive strain. When the strain is larger than 0.06%, the electric field can only change the strength of the magnetic anisotropy but cannot change its direction. When the strain is smaller than 0.06%, the electric field of 267 kV/cm can reorientate the easy axis by 90°. The present results may be helpful for designing flexible multiferroic devices with a suitable initial strain in order to realize the 90° reorientation of the magnetization. [ABSTRACT FROM AUTHOR]

We report magnetic interactions and electronic transport properties in La0.4Bi0.6Mn0.5Ti0.5O3 perovskite manganite synthesized using solid-state route. After characterizing the samples structurally, the systematic investigations of magnetic and electrical transport behaviors have been undertaken. It has been observed that at low temperatures near TC, the sample is magnetically frustrated leading to the second-order magnetic transition. A justification for the observed magnetic behavior has been explained based on Arrott’s plot study. The resistivity as a function of temperature in the absence and the presence of applied magnetic field suggests semiconducting nature of the sample. The conduction of the charge carriers is explained using Shklovskii-Efros-type variable-range-hopping mechanism. [ABSTRACT FROM AUTHOR]

The Technical Committee of the IEEE Magnetics Society has selected seven research topics to develop their roadmaps, where major developments should be listed alongside expected timelines: 1) hard disk drives; 2) magnetic random access memories; 3) domain-wall devices; 4) permanent magnets; 5) sensors and actuators; 6) magnetic materials; and 7) organic devices. Among them, magnetic materials for spintronic devices have been surveyed as the first exercise. In this roadmap exercise, we have targeted magnetic tunnel and spin-valve junctions as spintronic devices. These can be used, for example, as a cell for a magnetic random access memory and a spin-torque oscillator in their vertical form as well as a spin transistor and a spin Hall device in their lateral form. In these devices, the critical role of magnetic materials is to inject spin-polarized electrons efficiently into a nonmagnet. We have accordingly identified two key properties to be achieved by developing new magnetic materials for future spintronic devices: 1) half-metallicity at room temperature (RT) and 2) perpendicular anisotropy in nanoscale devices at RT. For the first property, five major magnetic materials are selected for their evaluation for future magnetic/spintronic device applications: 1) Heusler alloys; 2) ferrites; 3) rutiles; 4) perovskites; and 5) dilute magnetic semiconductors. These alloys have been reported or predicted to be half-metallic ferromagnets at RT. They possess a bandgap at the Fermi level EF only for its minority spins, achieving 100% spin polarization at EF . We have also evaluated \textL10 alloys and D022 –Mn alloys for the development of a perpendicularly anisotropic ferromagnet with large spin polarization. We have listed several key milestones for each material on their functionality improvements, property achievements, device implementations, and interdisciplinary applications within 35 years time scale. The individual analyses and the projections are discussed in the following sections. [ABSTRACT FROM AUTHOR]

Exploiting both spin and charge of the electron in electronic micordevices has lead to a tremendous progress in both basic condensed-matter research and microelectronic applications, resulting in the modern field of spintronics. Current spintronics relies primarily on ferromagnets while antiferromagnets (AFMs) have traditionally played only a supporting role. Recently, antiferromagnets have been revisited as potential candidates for the key active elements in spintronic devices. In this paper, we review approaches that have been employed for reading, writing, and storing information in AFMs. [ABSTRACT FROM AUTHOR]

Most thin magnetic films have their magnetization in the plane of the film because of shape anisotropy. In recent years, there has been a resurgence of interest in thin magnetic films that exhibit a magnetization easy axis along the surface normal due to so-called perpendicular magnetic anisotropy (PMA). PMA has its origins in the symmetry breaking that occurs at surfaces and interfaces and can be strong enough to dominate the magnetic properties of some material systems. In this talk, I explain the physics of such materials and show how the magnetic properties associated with PMA are often very well suited to applications. I show three different examples of real and potential applications of PMA materials: ultralow power spin-transfer-torque magnetic RAM devices for low-energy computing, three-dimensional (3-D) magnetic logic structures, and a novel form of cancer therapy. [ABSTRACT FROM AUTHOR]

An important step has been developed combining the potential of spintronics with organic electronics to reveal the promising field of molecular spintronics, which can offer more flexibility, higher recyclability, and low-production costs compared with inorganic devices. Room temperature magnetoresistance (MR) of 5% has been obtained from C60 spin valves with the structure Co(20 nm)/Al2 O3(1.2 nm)/C60 (5–60 nm)/Py(20 nm)/Al(1.5 nm). We observe an asymmetric dependence at low temperatures of the MR with voltage, and surprisingly with the magnetic field as well. This behavior has been attributed to the organic interface formed at the junction, which results in a change of the ferromagnet’s spin polarization. The spin polarization at the organic-ferromagnetic interface is extracted by measuring the bias dependence of the conductance of a metallic-superconducting point contact and analyzed the spectra with the modified Blonder–Tinkham–Klapwijk theory. Point-contact Andreev reflection measurements reveal that the Co–C60 possess spin polarization of 30% ± 1%, compared with 40% ± 1% for our Co films without C60. This could account for the asymmetry of the MR in spin valves incorporating C60 and the need for an alumina spacer to maximize the MR. [ABSTRACT FROM AUTHOR]

From the spin–spin interaction, spin-capacitive term is defined in a similar way to the usual charge capacitive term that is due to the charge–charge interaction. The charge and spin capacitive effects between the gate and central channel region are found to play an important role in gate-controlled spin-dependent transport systems. Both the capacitive terms affect system’s charge and spin ac transport properties. The behaviors of conductance, density of states, and internal potentials demonstrate the strong involvement of charge and spin in electrons in spin-dependent transport. The purpose of this paper is to draw attention to the Coulomb and exchange interactions in spintronics devices. [ABSTRACT FROM AUTHOR]

This paper presents an energy harvester using a Terfenol-D/PMNT/Terfenol-D magnetoelectric (ME) transducer for scavenging ac magnetic field energy from two-wire power cords connected to household and commercial appliances. The harvester uses a magnetic circuit consisting of six NdFeB magnets mounted on the free end of a cantilever beam. The magnets produce concentrated flux gradient on the ME transducer, and the vertical Ampere forces acting on the two conductors of the power cord are superimposed. An enhanced movement is then induced on the magnetic circuit. The ME transducer undergoes magnetic field variations and generates power output. A prototype is fabricated and tested. Because of the high magnetomechanical coupling effect of the magnetostrictive material and the large flux gradient on the ME transducer, the harvester can generate a maximum power of 671.2 \(\mu \) W with a matching load resistance of 991 k \(\Omega \) at 6 A. The results demonstrate the potential of the proposed device applied to electricity end-use environment in electric power systems. [ABSTRACT FROM AUTHOR]

An external strain is suggested as an effective means to finely control the magnetic properties of a candidate medium for future spintronics devices. To demonstrate the potential of this concept, the biaxial strain effects on the magnetic moment of Co adatom on pyridinic N-doped graphene (PNG) sheet were investigated using density functional theory calculations. Under the strain from −5% to 5%, the magnetic moment of the Co adatom on PNG was increased continuously from 1.72 to \(1.95 \mu {_{B}}\) . Also, Co adatoms are expected to be dispersed on the PNG surface without metal clustering in this range of applied strain due to its strong binding with the pyridinic nitrogen defects. From these results, it is anticipated that reliable control of magnetism in Co decorated PNG system is available by use of an external strain. [ABSTRACT FROM AUTHOR]

Spin Hall effects convert charge currents into spin currents and vice versa even in nonmagnetic conductors due to spin orbit coupling. This enables spin Hall effects to be utilized both for the generation and detection of spin currents and magnetization dynamics. This paper reviews the experimental characterization of these effects in metallic systems, which have so far shown the highest efficiency in using spin Hall effects for charge-to-spin interconversion. The advantages and disadvantages of complimentary measurement techniques are discussed and in addition an outlook of the possible impact on applications is presented. [ABSTRACT FROM AUTHOR]

The application of an electrical forward bias across a ferromagnet/semiconductor Schottky barrier can result in a non-equilibrium spin accumulation in the semiconductor. This mechanism is referred to as spin extraction. Like spin injection, spin extraction can also serve to generate the electron spin polarization, which is necessary for the operation of a local spin valve, i.e., a magnetoresistance device consisting of a ferromagnetic/non-magnetic/ferromagnetic hybrid structure, which exhibits an electrical resistance that depends on the relative orientation of the magnetizations of the two ferromagnetic electrodes. In such a spin extraction spin valve (SESV), a spin-polarized drift current is generated in a non-magnetic channel by spin extraction at a ferromagnetic electrode. The spin polarization influences the output current through a subsequent ferromagnetic electrode. We show how spin valve devices relying on multiple spin extraction events can be used for magneto-logic gate operation. Furthermore, we investigate the potential use of these structures as sources of highly spin-polarized drift currents. [ABSTRACT FROM AUTHOR]

We present the experimental realization of a full adder circuit using Nanomagnet Logic (NML). The circuit relies heavily on the properties of asymmetric slant magnets that allow robust operation and reduced footprint. We demonstrate stand-alone NML majority gates and wires, and interconnect these components into an NML full adder that functions properly for all 8 input combinations. To our knowledge, this is the first working implementation of an NML full adder from in-plane magnetized nanomagnets, and one of the very few existing non-electrical, room temperature nanoscale computing units. [ABSTRACT FROM AUTHOR]

This article reports a comparative study of the spin pumping induced by graphite and graphene layers adjacent to an extended ferromagnetic Permalloy film. The corresponding enhancement of the Gilbert damping in the ferromagnet is determined by analyzing the frequency dependence of the ferromagnetic resonance linewidth in experiments done with a broad band microwave spectrometer. The results show that a single graphene layer is more efficient than a thick graphite film in absorbing the angular momentum pumped away from the Permalloy during the resonant precession of its magnetization. We associate this effect to an enhancement of the spin-orbit coupling in the graphene layer due to Copper adatoms residual from the chemical vapor deposition process used to synthesize the graphene used in the experiments. [ABSTRACT FROM AUTHOR]

The influence of injected current on magnetization dynamics is investigated in submicrometer-wide strips of out-of-plane magnetized Pt/Co/GdOx. This ultrathin film structure is similar to Pt/Co/AlOx exhibiting highly efficient current-driven domain wall (DW) motion, which has recently been attributed in part to the Rashba effect. In Pt/Co/GdOx, the reduction of the out-of-plane magnetization with increasing injected current is largely due to Joule heating, and the effective transverse Rashba field that tilts the magnetization is estimated to be at most \sim0.3 T/(10^12 A/m^2). Measurements of high-speed DW motion reveal no evidence of a strong Rashba field to suppress DW precession. These findings indicate that the Rashba effect plays a limited or negligible role in current-driven DW dynamics, and alternative torques are required to explain the high efficiency of DW motion in ultrathin heavy-metal/ferromagnet/oxide systems. [ABSTRACT FROM AUTHOR]

Nonlinear modulators, of any physical nature, exhibit a frequency spectrum in which sidebands, while always symmetrically located with respect to the central peak, generally present different amplitudes. In this paper, a systematic theoretical study on the possibility to achieve a symmetry also in the sidebands amplitudes is carried out. This amplitude symmetry property is investigated for pure and combined, linear and nonlinear, analog modulation schemes. A validation of our theoretical results is achieved through a numerical study performed on a nonlinear spintronic modulator. [ABSTRACT FROM AUTHOR]

Spintronics is an emerging platform for logic circuit design. Though many approaches have been proposed, and several have met with some success, a number of challenges remain. Here, we introduce a new style of magnetic logic—mLogic—enabled by a novel four-terminal device. An input current pulse to the device switches the magnetic state by spin transfer torque-driven domain wall motion, which programs the resistance state of a magnetic tunnel junction in an electrically-insulated but magnetically-coupled path. Despite the low switching ratios of the devices, limited by the tunnel magnetoresistance ratio, logic circuits independent of CMOS may be configured using current-based signaling. Micromagnetic analysis of device performance and the concepts of mLogic circuit design are introduced, with SPICE simulation of logic gates demonstrating correct logic operation at supplies below 100 mV. [ABSTRACT FROM AUTHOR]

The effects of a noise-like weak signal in the resonant switching of the magnetization driven by spin transfer torque have been systematically studied by means of micromagnetic simulations in both in-plane spin valves and out-of-plane magnetic tunnel junctions. The use of a noise-like resonant excitation allows the overpassing of some critical points compared to the traditional microwave assisted switching. In particular, the application of binary spreading sequences (BSS) does not require the precise knowledge of the resonant frequency and of the optimum relative phase, allowing the use of the same resonant excitation for all the devices in a matrix of memory cells, even if small variations of the physical and geometrical parameters are present. In addition, we also found that in spin valves the switching probabilities close to 100% can be achieved with a smaller current pulse, and in magnetic tunnel junctions a significant energy saving can be obtained. [ABSTRACT FROM PUBLISHER]

We have performed first-principles calculation to investigate the magnetic exchange interactions of 3-D transition metals (TMs) adatoms on graphene. Our study found that the most stable adsorption sites and geometries of different 3-D TM dimmer adatoms on graphene are obviously distinct. The obtained magnetic exchange energies indicate that Fe and Co adatoms on graphenes are always ferromagnetic coupling. Thus, they may be a candidate of graphene-based spintronics devices. Furthermore, electronic structure analysis shows that mechanism of ferromagnetic interaction of 3-D TMs adatoms on graphene is either direct exchange (two TMs adatoms are on the same side of graphene) or superexchange (two TMs adatoms are on the two sides of graphene). [ABSTRACT FROM AUTHOR]

This paper formulates a general analytic approach to the theory of microwave generation in magnetic nano-structures driven by spin-polarized current and reviews analytic results obtained in this theory. The proposed approach is based on the universal model of an auto-oscillator with negative damping and nonlinear frequency shift. It is demonstrated that this universal model, when applied to the case of a spin-torque oscillator (STO) based on a current-driven magnetic nano-pillar or nano-contact, gives adequate description of most of the experimentally observed properties of STO. In particular, the model describes the power and frequency of the generated microwave signal as functions of the bias current and magnetic field, predicts the magnitude and properties of the generation linewidth, and explains the STO behavior under the influence of periodic and stochastic external signals: frequency modulation, phase-locking to external signals, mutual phase-locking in an array of STO, broadening of the generation linewidth near the generation threshold, etc. The proposed nonlinear auto-oscillator theory is rather general and can be used not only for the development of practical nano-sized STO, but, also, for the description of nonlinear auto-oscillating systems of any physical nature. [ABSTRACT FROM PUBLISHER]

The correlation between the direct magnetoelectric (ME) effect and the magnetization of planar ferromagnetic (FM)–piezoelectric composite structures has been demonstrated. It is experimentally proved that for unsaturated layers of FM galfenol, permendur, amorphous alloy, and nickel, the magnetostriction is the quadratic function of the magnetization. Using a langatate-nickel structure with magnetic hysteresis as an example, it has been shown that the dc magnetic field dependence of ME interaction efficiency can be calculated and predicted using magnetization curves for the FM layer. [ABSTRACT FROM AUTHOR]