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The spin–orbit torque via the spin Hall effect of heavy metals has shown promising prospect in driving the magnetization switching in spintronic devices due to the generated spin current from heavy metals. Recently, the 3d-light metals have been predicted the ability to generate orbital current and the associated orbital torques from the orbital Hall effect. However, few experiments have been carried out since it is quite hard to directly detect the orbital current-generated orbital torque. Here, we report an effective method to demonstrate the strong orbital torques in light metal Cr through a conversion process from orbital current to spin current by introducing the Pt interfacial layer in perpendicularly magnetized symmetric Pt/Co/Pt structures. A quite large and monotonically growth of orbital torque efficiency in Pt/Co/Pt/Cr with the increase of the thickness of Cr layer is obtained with the largest effective orbital torque efficiency around 2.6 Oe/(MA⋅cm−2) (1 Oe = 79.5775 A⋅m−1). The ability of orbital torque to drive the magnetization switching is also reported with the critical switching current density down to the order of 106 A⋅cm−2. Our findings prove the efficiency for switching the magnetization from light metal Cr layers through the orbital Hall effect.

Synthetic antiferromagnets (SAFs) with perpendicular magnetic anisotropy (PMA) have recently attracted intensive attention for their potential applications in domain-wall-based racetrack memory. In this paper, swift heavy Fe ion irradiation is introduced to tune the magnetic properties of Pt/Co/Pt/Ru/Pt/Co/Ta SAFs from spin-flip to spin-flop transition. The evolutions of magnetic domain and domain wall motion are investigated to obtain the microscopic insight into the change of magnetic states. Both the experimental and the simulated results demonstrate that different responses of the effective PMA constant and the interlayer-exchange-coupling strength to ion irradiation determine the magnetic-phase transitions. The structure evolution from experiments and theoretical simulations suggests that the ion-irradiation-induced damage mainly happens at the Pt/Co interface. The damage leads to the different decrease rates of the effective PMA constant and the interlayer-exchange-coupling strength due to their intrinsic direct and Ruderman-Kittel-Kasuya-Yosida interaction nature, respectively. A quite good thermal stability of samples is obtained with ion fluence $l1.5\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{0.16em}{0ex}}\mathrm{ions}/\mathrm{c}{\mathrm{m}}^{2}$. In this paper, we demonstrate that ion irradiation is a promising method to tailor magnetic properties of SAFs. Additionally, the ion-irradiation-induced well-controlled antiferromagnetically coupled domains could show potential applications in spintronic devices.

The spin–orbit torques originating from the spin Hall effect of heavy metals are of vital importance for applications in spintronics due to its low consumption of energy. Theoretical calculations have predicted that 3 d and 4 d light metals can produce a similar amount of torques to heavy metals via the strong orbital Hall effect (OHE). However, few experiments have been conducted since it is technically challenging to directly detect the orbital current from the OHE. Here, we report an effective approach to demonstrate the strong orbital torques in the light metal Cr with the aid of a conversion process from the orbital current to the spin current by introducing an Au interfacial layer in the Cr/ferromagnet structures. A rather large orbital torque efficiency and an increase with the increasing thickness of the Cr-layer are attained in the perpendicularly magnetized Cr/Au/Co/Ti multilayers. Moreover, an energy efficient magnetization switching and the domain wall motion in Cr/Au/Co/Ti multilayers induced by the OHE have also been observed. Our findings confirm the existence of the orbital Hall torques in Cr and provide an effective way to investigate the OHE.

The effect of the thicknesses of Pt and the insertion of Al layer on the effective magnetic damping constant of CoFeB/Pt thin films caused by the spin-pumping effect has been studied by an angular-dependent ferromagnetic resonance method. In CoFeB/Pt bilayers, a roughly linear dependence of the effective damping constant on Pt thickness ( $t{\mathbf {Pt}}$ ) was observed before saturated at $t_{\mathbf {Pt}} = 2$ nm. While in CoFeB/Al/Pt trilayers, a sharp drop of damping constant was observed while Al thickness is around 0.5 nm, then the damping constant nearly remains when Al thickness further increases to 5 nm. It indicates a decreased spin pumping efficiency due to Al insertion between CoFeB and Pt layers. The decreased spin pumping efficiency was ascribed to the spin memory loss at CoFeB/Al and/or Al/Pt interfaces rather than the spin backflow effect. The results also suggest that the linearly increased damping constant in CoFeB/Pt layers mainly comes from the magnetic proximity effect (MPE) of Pt, which could be eliminated by insertion a thin layer of Al. However, in order to obtain a large-spin current injection efficiency and less MPE to improve the spin-pumping effect in CoFeB/Pt, a proper insertion layer rather than Al with small-spin memory loss need to be investigated.

Spin-pumping and spin-orbit torque efficiencies in ferromagnetic/heavy metal bilayers, which usually consist of the polycrystalline grains, are related to the spin current transmission from ferromagnets to heavy metals and vice versa, respectively. In this work, epitaxial ${\mathrm{Fe}}_{0.79}{\mathrm{Si}}_{0.21}(001)/\mathrm{Pt}(111)$ films were fabricated to investigate the spin-pumping efficiency and spin-orbit torque efficiency by ferromagnetic resonance and harmonic Hall resistance measurement techniques, respectively. Ferromagnetic resonance results show that the incremental magnetic damping constants in epitaxial ${\mathrm{Fe}}_{0.79}{\mathrm{Si}}_{0.21}(001)/\mathrm{Pt}(111)$, compared with those of the epitaxial ${\mathrm{Fe}}_{0.79}{\mathrm{Si}}_{0.21}(001)/\mathrm{Al}{\mathrm{O}}_{x}$ reference sample, depend on whether the external magnetic field is applied along the in-plane easy or hard axes of ${\mathrm{Fe}}_{0.79}{\mathrm{Si}}_{0.21}$. The Pt thickness-dependent anisotropic damping constant was ascribed to the anisotropic spin current absorption in epitaxial Pt(111) layer. When electric currents were applied along the easy and hard axes of ${\mathrm{Fe}}_{0.79}{\mathrm{Si}}_{0.21}$ in epitaxial ${\mathrm{Fe}}_{0.79}{\mathrm{Si}}_{0.21}(001)/\mathrm{Pt}(111)$ bilayers, a large difference between spin-orbit torques generated from Pt(111) was observed by a harmonic Hall resistance measurement method. Both of the results suggest that spin current transmission efficiency is related to the anisotropic spin Hall effect of epitaxial Pt(111) layer due to the different spin-orbit interaction energies along the different crystallographic directions of Pt.

Lead-free piezoelectric nano-based generator with energy harvesting has drawn a great attention in the recent years. BaTiO3 as a lead-free material with high piezoelectric coefficient and dielectric constant has been widely examined to realize nanogenerators. In this work, high-quality BaTiO3 (BTO) nanowires were prepared by hydrothermal synthesis as the piezoelectric material and then BTO/PVDF-based nanogenerators have been fabricated. Furthermore, the CNTs were added to improve the output voltage performance of the nanogenerator. It shows high performance of a maximum output voltage density of 7.3 V/cm2 and the stable current density of 3.3 nA/cm2. This hybrid nanogenerator with enhanced performance is a potential material for the application in harvesting energy, self-powered electronics and low-frequency capacitors.

Increasing spin Hall angle of heavy metals has attracted considerable attention due to their potential applications in spintronic technology. Here, we demonstrate that the spin Hall angle could be enhanced dramatically in the Ta/[Pt/Ru]n/Pt/Co/Ta multilayers. The spin Hall angle reaches a maximum value of 0.28 when n = 5 from the loop-shift method with a relative low resistivity of approximately 48 μΩ cm. Meanwhile a minimum critical switching current density approximately 3.2 × 106 A/cm2 under an in-plane bias magnetic field around 5% of the perpendicular anisotropy field was obtained for the sample with n = 5 in current-induced magnetization switching experiment. We find that the extrinsic spin Hall mechanism changes from the spin skew scattering when n 2. This work provides an effective way in increasing spin Hall angle for low-power consumption spintronics devices.

Summary Carbon-based supercapacitors (SCs) are important electrochemical energy storage devices and are often used in electronic equipment that generates a magnetic field. However, whether the magnetic field affects the charge storage of SCs is unknown. Here, we discover that applying an external magnetic field to carbon-based SCs can induce capacitance change in both aqueous acidic and alkaline electrolytes but not in neutral electrolytes. We further show that, in KOH electrolytes, the competition between the driving force caused by the Lorentz force and the damping force related to the electrolyte conductivity plays a crucial role in affecting the OH− transport under the magnetic field. In H2SO4 electrolytes, the third paramagnetic force generated by the paramagnetic H+ under the magnetic field hinders the H+ transport in addition to the above forces. A quantitative relationship among the limiting current density at the electrode-electrolyte interface, the intensity of the magnetic field, and the concentration and viscosity of electrolytes can therefore be established.

Current induced spin–orbit torque (SOT) in heavy metals with strong spin–orbit coupling strength has attracted considerable attention due to its potential applications in spintronic technology. Pt, as one of the mostly used heavy metals in SOT-based spintronic devices, shows large spin Hall angle (θSH) with its single phase and alloy counterparts. In this work, the in-plane crystallographic orientations related θSH of epitaxial Pt(111) layer is reported in MgO(111)/Pt(111)/Co/Ta heterostructures with strong perpendicular magnetic anisotropy. The θSH shows a quite large difference with values, respectively, around 0.083 and 0.057 when the current applied along the [ 1 1 ¯ 0 ] and [ 11 2 ¯ ] crystallographic directions of Pt(111) by the damping-like SOT efficiency using the harmonic Hall voltage measurement technique. The critical switching current densities also show large difference between these two orthogonal crystallographic orientations with the trend of that the larger SOT efficiency leads to the smaller critical switching current density. It independently confirms the generation of different damping-like SOT efficiency when current along [ 1 1 ¯ 0 ] and [ 11 2 ¯ ] directions of Pt(111). Moreover, a perpendicularly magnetized Pt/Co/Ta reference heterostructures with Pt having polycrystalline phase shows tiny variation of damping-like SOT efficiency in in-plane two orthogonal directions, which also indirectly indicates the crystallographic orientations related θSH in epitaxial Pt(111) layers. This study indicates that the θSH of epitaxial Pt is a crystallographic orientations related parameter.

Epitaxial FeSi film on MgO (001) substrate was fabricated via a radio frequency magnetron sputtering technology. The epitaxial relationship of FeSi(001)/[110]//MgO(001)/[100] was characterized by crystal structure measurements and confirmed by in-plane biaxial magnetic anisotropy through vibrating sample magnetometer (VSM). By measuring Kerr magnetic hysteresis loops and recording the real-time magnetic domain images through surface magneto-optic Kerr effect (MOKE), two successive 90° domain wall displacement along easy axis and two discontinuous 90° domain wall displacement along hard axis were directly observed. Meanwhile, the difference of magnetic hysteresis loops obtained by VSM and MOKE devices were discussed. Furthermore, from the results of magnetic field sweeping ferromagnetic resonance measurements, it was found that FeSi film possesses an anisotropic effective damping constant of 0.0042 for easy axis direction and 0.0053 for hard axis direction, which was ascribed to the crystallographic defects induced two magnon scattering contributions.

The choice and configuration of the ferroelectric (FE) substrate and the ferromagnetic (FM) layer in FM/FE heterostructures play an important role in magnetism modification with regard to amplitude and efficiency. In this study, we fabricated FeSi films on low crystalline (011) [Pb(Mg1/3Nb2/3)O3]0.7-[PbTiO3]0.3 (PMN-0.32PT) using radio frequency magnetron sputtering. In the annealed FeSi/(011) PMN-0.32PT heterostructures, the FeSi film presented with a (011) preferred orientated polycrystalline structure and low magnetocrystalline anisotropy. Both loop-like and butterfly-like magnetism modifications were observed by applying bipolar electric fields, and the weak and abnormal electrically mediated magnetism behaviors were significantly different from the prominent magnetic anisotropy transition in FeSi/(011) PMN-0.3PT. The comparative analyses suggest that the resulting high-quality single-crystalline PMN-xPT and FM films with low coercivity are of great significance for exploring giant, reversible, and non-volatile magnetism regulation.

In a bilayer system of Bepp2-FeCo, the element content variation and chemical states of the Bepp2-FeCo interface were investigated using X-ray and ultraviolet photoelectron spectroscopy with Ar ion etching. Chemical reaction was observed for Co and Fe with Bepp2 at the interface. Ultraviolet photoelectron spectroscopy results showed a downward energy shift of -1.0 eV at the interface. This behavior was attributed to the formation of an interface dipole layer. The hole injection barrier Phi(P)(B) was 2.0 eV, and the electronic injection barrier Phi(n)(B) was 0.6 eV. Moreover, only as the FeCo thickness is less than 3 nm, an uniaxial anisotropy can be induced on the organic layer with the investigation of magnetic optical Kerr effect, this can be used as a multi-function devices. (C) 2016 Elsevier B.V. All rights reserved.

The interaction at organic–ferromagnetic interfaces in organic spin-valves has a considerable effect on efficient spin injection or detection. In this work, Al/Co films were deposited on the organic Bepp2 layers at two different substrate temperatures to investigate the interface interaction. The interaction including penetration, interdiffusion and chemical reaction has been studied by the surface morphology measurement, X-ray photoelectron spectroscopy combined with Argon ion etching technique and magnetic properties measurement. It was found that the interfacial penetration and chemical reaction were serious, forming plenty of holes and non-ferromagnetic metallic carbide and oxides owing to the high energy of sputtered Co atoms into the organic Bepp2 layer when depositing Co on Bepp2 layer at the substrate temperature of 24 °C. However, this phenomenon weakened when lowering the temperature to −13 °C. Our results show that the low substrate temperature can reduce the penetration of the top metal electrode into the organic layer and weaken the chemical reaction between the top electrode and organic layer, which could pave a way for obtaining high-spin injection and extraction efficiency in organic spin-valve devices.

Spin orbit torque-driven magnetization switching in perpendicularly magnetized thin film relies on an extra in-plane magnetic field to break the in-plane magnetic symmetry, which is an obstacle for the integration of spin–orbit torque-based spintronic devices. Here, we propose a simple method to realize the field-free spin–orbit torque-driven magnetization switching by exploiting a tilted magnetic anisotropy, which is caused by the direct coupling of two ferromagnetic layers in the Pt/Co/FeNi/Ta structure. When preparing the sample, a 1000 Oe in-plane magnetic field was applied to ensure the magnetic moment deviating a small angle from the out-of-plane direction to this in-plane field direction. We experimentally demonstrate the deterministic field-free magnetization switching in Pt/Co/FeNi/Ta by the field-like spin–orbit torques when the electric current is applied perpendicular to this in-plane field direction. The switching performance is slightly degraded with the critical switching current density and thermal stability factor, respectively, reaching 6.4 × 106 A/cm2 and 25 due to the slightly decreased spin–orbit torque efficiency and perpendicular magnetic anisotropy with introducing the FeNi layers. Our work paves the way for realizing the field-free magnetization switching by spin–orbit torques.

The interfacial Dyzaloshinskii-Moriya interaction (DMI) plays a crucial role in stabilizing a chiral Neel-type magnetic domain wall in perpendicularly magnetized multilayers. In this work, we investigate the effect of oxide layers on interfacial DMI in ultrathin Pt/Co/SmOx and Pt/Co/AlOx stacks with the perpendicular magnetic anisotropy. The DMI effective field was characterized using the field driven domain wall creep and current-induced hysteresis loop shift methods. The experimental results show that an enhanced interfacial DMI is obtained in Pt/Co/SmOx stacks, which may be related to the oxidation degrees of the Co layer in view of the difference of Co/metallic oxide interfaces. Moreover, the X-ray photoelectron spectroscopy with the argon ion etching technique was used to further verify the weaker oxidation of the Co layer existed in Pt/Co/SmOx than that in Pt/Co/AlOx in the same annealing process due to the smaller electronegativity of the Sm compared to the Al element. Our results provide a promising route to effectively manipulate the interfacial DMI in spin-orbit-torque-based spintronic devices through the element electronegativity.

The (011) Pb (Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT)/Ni heterostructure was prepared, and the influence of light on magnetization reversal behaviors of the Ni layer was investigated. We found that the ferroelectric domain of the PMN-PT substrate was tuned by a photostrictive effect, and it further changes the magnetization state of the adjacent Ni layer. Additionally, with electric field polarization, the PMN-PT/Ni heterostructure exhibits controllable magnetization switching behaviors under the application of a proper light intensity. It provides a reliable way to manipulate the magnetization switching process, which is promising for the design and implementation of low power memory and spintronic devices.

Domain wall (DW) motion via current induced spin-orbit torque (SOT) and/or a magnetic field in ferromagnet/heavy metal heterostructure has attracted abundant interests due to its potential applications in magnetic memories and logic devices. In this work, we study the influence of the depinning energy barrier on DW motion in the creep regime using the polar magneto-optical Kerr microscopy in the Cr layer decorated Pt/Co/Ta structure. We find that although the SOT efficiency shows a significant enhancement in the Pt/Co/Cr/Ta system, but the current-induced DW motion efficiency still shows an attenuation. We confirm that this unexpected result is caused by the enhanced pinning energy barrier, extracted from the relationship between the cumulative depinning probability (Pd) and the depinning time (t). Moreover, the relationship between Pd and t exhibits preferred exponential distribution, indicating that a single energy barrier governs the depinning behavior in our systems. We also reveal that the energy barrier depends on the interface between the ferromagnet and heavy metal. Our study suggests that the current-induced DW motion efficiency is not only determined by the SOT efficiency, but also the depinning energy barrier.

Laser induced magnetization dynamic behaviors of SmxFe1-x thin films with tunable x (0.25x0.5) are investigated by the time-resolved magneto-optical Kerr effect. It is found that the demagnetization process is accomplished by a two-stage process, the demagnetization time of stage I is within 1.0 ps (t1) for all the samples with different x, while it increases from 0 to 16 ps at stage II (t2) due to the reduced exchange coupling. By introducing an additional magneto-elastic energy contribution, the dispersion relation of precession frequency is deduced, by which the field-dependent frequency curves are well fitted.

Heavy metal/ferromagnetic layers with perpendicular magnetic anisotropy (PMA) have potential applications for high-density information storage in racetrack memories and nonvolatile magnetic random access memories. In these devices, deterministic magnetization switching has been achieved via electric current induced spin orbital torques (SOTs) with the assistance of a current directional external in-plane bias field, which causes technological obstacles for the real application of SOT based spintronic devices. Here, we report that reversible field-free magnetization switching could be achieved via current-driven domain wall motion (DWM) in Pt/Co/Cr micro-sized racetracks with PMA owing to the preformation of the homochiral Neel-type domain wall, in which an in-plane inherent Dzyaloshinskii-Moriya interaction field was generated acting as the external in-plane bias field to break the symmetry. A full magnetization switching can be realized in this device based on the enhanced SOTs from a dedicated design of Pt/Co/Cr structures with Pt and Cr showing opposite signs of spin Hall angles. Therefore, the generated spin currents are expected to work in concert to improve the SOTs. We also demonstrated that the simultaneously accompanying Joule heating effect also plays a key role in the field-free magnetization switching process, including the propagation field as well as the domain wall motion velocity.

The estimation of the DMI effective fields and SOT efficiency as well as the influence of an in-plane bias field Hx or Hy on the anomalous Hall loops. (DOCX 529 kb)

Self-assembled flowerlike alpha-Fe2O3, Fe3O4 and gamma-Fe2O3 were fabricated by a simple calcination procedure. The structure characterization shows that the flowerlike morphology and the size of the nanostructures are perfectly maintained in the conversion of precursor to a-Fe2O3, Fe3O4, and gamma-Fe2O3. The complex permittivity and permeability results indicate that the dielectric and magnetic loss of Fe3O4 flower are both higher than those of gamma-Fe2O3 flower. In addition, Fe3O4 flower shows a good electromagnetic impedance match and its microwave absorption mainly originates from magnetic loss rather than dielectric loss. An optimal reflection loss of -46.0 dB is found at 3.4 GHz for flowerlike Fe3O4, which indicates that the sample can be used as a highly efficient microwave absorber. (C) 2015 Elsevier B.V. All rights reserved.

The interface between the organic and magnetic electrodes is a fundamental problem in organic spintronics devices. Therefore, bilayer structure of Alq(3)/FeCo was fabricated in a dual ultra high vacuum chamber. The electronic structure of Alq(3)-FeCo interface has been studied by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy with Argon ion etching technique. It was found that organic layer reacts partially with the FeCo film, forming complex binding of metallic carbide and/or oxidation state in the interfacial region. Electronic injection barrier is 0.76 eV in the interface. The structural variation of the contact region is proposed to be one of the possible factors resulting in spin-injection failure. The magnetic properties of FeCo film with different thicknesses on glass substrate and Alq(3) layer are also investigated. The induced uniaxial anisotropy only presents in 3 nm FeCo thickness for glass/FeCo, while it appears in 3-5 nm FeCo for Alq(3)/FeCo. (C) 2015 Elsevier B.V. All rights reserved.

FeCo films with various thicknesses were fabricated by direct-current magnetron sputtering on corning glass and organic ferroelectric PVDF substrates at the same time with 5 nm Ru seed layer and 5 nm Ta protective layer. The in-plane uniaxial anisotropy field of FeCo on glass substrate increases from 24 to 36 Oe with the increase of FeCo film thickness from 5 to 100 nm. However, a large in-plane anisotropy field of FeCo on PVDF substrate increases with FeCo thickness from 5 to 20 nm and gradually decreases with the FeCo thickness further increasing. Atomic force microscope images of FeCo on glass show quite smooth surface with root-mean-square roughness around 0.5 nm and have none visible granules on the surface for all samples. While, AFM images of FeCo on PVDF show quite rough surface with RMS roughness around 25 nm and have visible granules with the smallest granules appearing at the FeCo thickness of 20 nm. The permeability spectra show the typical ferromagnetic resonance phenomenon and can be well fitted by the LLG equation with the obtained experimental parameters. The ferromagnetic resonance frequency can reach 7.0 GHz for the 20 nm FeCo film on PVDF. Moreover, the quality factor of this sample can respectively reach 26, 12 and 7 at 1.0, 2.0, and 3.0 GHz, indicating the potential real 3G application for high-frequency devices.

The interface has become an important issue in organic magnetic spin-valves. In this work, Si/FeCo/Ta, Si/FeCo/Bepp2/Ta, and Si/Bepp2/FeCo/Ta samples with the variation of the FeCo layer thickness were fabricated by direct-current magnetron sputtering for FeCo layers and the thermal evaporation method for Bepp2 layers. The interaction at the interfaces between the FeCo magnetic layer and Bepp2 organic layer was investigated by the traditional magnetic properties measurement and X-ray photoelectron spectroscopy with the Argon ion etching technique. The experimental results show that the interfacial reaction is strong when sputtering FeCo on Bepp2 layer due to the high energy of sputtered FeCo atoms in contrast with the weak interfacial reaction when evaporating Bepp2 on FeCo layer. Moreover, the capping layer of Ta is quite important to protect FeCo layer against oxidation from air either by direct contact or through Bepp2 layer. Our experiment is very helpful for fabricating organic spin-valves with high-spin injection efficiency.

Strip-like FeCo films were patterned by a traditional lithograph process from intrinsically isotropic continuous FeCo films. The strip-patterned FeCo film shows a strong in-plane uniaxial magnetic anisotropy with easy axis along the length direction of the strip. The angular dependences of remanence ratio, switching field, and coercivity indicate that the magnetization reversal mechanism of the strip-patterned FeCo film is coherent rotation and domain wall depinning when the applied field is near the hard axis and easy axis, respectively. The consistency of the experimental hysteresis loops of the strip-patterned FeCo film and calculated hysteresis loops with a simple in-plane uniaxial anisotropy model indicates that the strip-patterned FeCo film behaves as a single domain. The absence of the domain wall and the strong in-plane anisotropy field make the strip-patterned FeCo films have much potential for high-frequency application.

The field emission (FE) properties of vertically aligned carbon nanotube (CNT) arrays having a surface decorated with Ta layer were investigated. The CNTs with 6 nm thickness of Ta decoration showed improved FE properties with a low turn-on field of 0.64 V/mu m at 10 mu A/cm(2), a threshold field of 1.06 V/mu m at 1 mA/cm(2) and a maximum current density of 7.61 mA/cm(2) at 1.6 V/mu m. After Ta decoration, the increased emission centres and/or defect sites on the surface of CNTs improved the field enhancement factor. The work function of CNTs with Ta decoration measured with ultraviolet photoelectron spectroscopy decreased from 4.74 to 4.15 eV with increasing Ta thickness of 0-6 nm. The decreased work function and increased field enhancement factor were responsible for the improved FE properties of the vertically aligned CNTs. Moreover, a significant hysteresis in the cycle-testing of the current density with rising and falling electric field process was observed and attributed to the adsorption/desorption effect, as confirmed by the photoelectron spectrum. (C) 2014 Elsevier Ltd. All rights reserved.

In ferromagnet/heavy metal heterostructures, critical current density (JC) refers to the minimum current density required to generate spin–orbit torque (SOT) for effective magnetization manipulation, including switching of magnetization and moving of domain walls and magnetic skyrmions. This critical current density is a key factor for next-generation SOT-based magnetic random access memory, racetrack memory, and logic devices. In this work, the critical current density for magnetization switching and the thermal stability of Pt/Co/Ta heterostructures in response to ion irradiation are studied. It is found that ion irradiation represents a promising approach for the wide tuning of the magnetic properties, such as the coercive force and the perpendicular magnetic anisotropy constant. It is also found that JC is significantly reduced after 500 eV Ar+ irradiation. Meanwhile, the ratio between the thermal stability factor E/kBT and JC increases with an increase in the irradiation dose, although E/kBT decreases slightly with the irradiation dose. This work demonstrates that JC can be significantly reduced by an appropriate ion irradiation process and thereby demonstrates a promising approach for effective reduction of the power consumption in SOT-based spintronic devices.

We study the perpendicular magnetic anisotropy (PMA) and spin–orbit torques (SOTs) in Pt/Co/Cr stacks as a function of Cr thickness. An enhanced PMA is observed and ascribed to the strong interfacial anisotropy between Co and Cr. Moreover, SOTs induced magnetization switching is achieved under relatively small critical current density in the order of 106 A cm−2 due to the enhanced effective spin Hall angle up to 0.15–0.27. Significantly, the linear dependence between and the square of longitudinal resistivity suggests that the spin Hall effect may arise from the intrinsic mechanism in our systems.

The field emission behavior of aligned carbon nanotubes (CNTs) is remarkably improved by decorating their surfaces with Ti nanoparticles through a sputtering process. The CNT/Ti(4 nm) sample shows a low turn-on field of 0.63 V/lm at 10 mu A/cm(2), low threshold field of 1.06 V/mu m at 1 mA/cm(2), and maximum field emission current density of 23 mA/cm(2) at 1.80 V/mu m. The enhanced field emission properties of the CNT/Ti samples are attributed to the added defect sites and Ti nanoparticles, which increase the field enhancement factor and density of emission sites. Stability measurements indicate that the Ti coating, which acts as a protective layer, also strengthens the field emission stability of the CNT arrays. Moreover, the extent of hysteresis in the current-voltage sweep highly depends on the voltage-sweep speed. (C) 2013 Elsevier B.V. All rights reserved.

Ultrafast spin dynamics in Tbx(FeCo)1-x films is studied using the time-resolved magneto-optical Kerr effect. At pump fluence of 1.0 mJ/cm2 the ultrafast demagnetization processes are accomplished by one-step and two-step decays (the first fast and second slow decays) for low and high Tb contents, respectively. For the low Tb contents (x

Co2FeAl nanoparticles were synthesized by reducing the coprecipitated precursor of CoCl2·6H2O, Fe(NO3)3·9H2O and Al2(SO4)3·18H2O under H2 atmosphere with various annealing temperatures and durations. X-ray diffraction and transmission electron microscopy were used to characterize the crystal structure and microstructure of Co2FeAl particles, respectively. The investigation indicates that the crystal structure of Co2FeAl particles tends to be B2 structure, in which atoms are partially ordered. The saturation magnetization and hyperfine field of Co2FeAl particles, which were measured under a vibrating sample magnetometer and a 57Fe Mossbauer spectroscope, are consistent with those of the bulk sample and thin films. Furthermore, the higher annealing temperature and the longer annealing time, the better crystallinity of Co2FeAl and more ordered arrangement of atoms will be. It turned out that the coprecipitation thermal deoxidization method could be an easy and high efficient way to obtain the half-metallic Co2FeAl nanoparticles.

The fi nding of an extremely large magnetoresistance effect on silicon based p–n junction with vertical geometry over a wide range of temperatures and magnetic fi elds is reported. A 2500% magnetoresistance ratio of the Si p–n junction is observed at room temperature with a magnetic fi eld of 5 T and the applied bias voltage of only 6 V, while a magnetoresistance ratio of 25 000% is achieved at 100 K. The current-voltage ( I–V ) behaviors under various external magnetic fi elds obey an exponential relationship, and the magnetoresistance effect is signifi cantly enhanced by both contributions of the electric fi eld inhomogeneity and carrier concentrations variation. Theoretical analysis using classical p–n junction transport equation is adapted to describe the I–V curves of the p–n junction at different magnetic fi elds and reveals that the large magnetoresistance effect origins from a change of space-charge region in the p–n junction induced by external magnetic fi eld. The results indicate that the conventional p–n junction is proposed to be used as a multifunctional material based on the interplay between electronic and magnetic response, which is signifi cant for future magneto-electronics in the semiconductor industry.

Spin-dependent transport property through molecules is investigated using a monolayer of oleic acid molecule self-assembled half metallic La 0.7 Sr 0.3 MnO 3 (LSMO) nanoparticles, which was synthesized using a coprecipitation method. Fourier transform infrared spectroscopy was used to confirm that one-monolayer oleic acid molecules chemically bond to the LSMO nanoparticles. The transport properties and magnetoresistance (MR) effect of the oleic acid molecule coated LSMO nanoparticles were measured by a direct current four probes method using a Cu/nanoparticle assembly/elargol electrode sandwich device with various temperatures and bias voltages. The non-linear I – V curve indicates a tunneling type transport properties. The tunnel barrier height around 1.3 ± 0.15 eV was obtained by fitting the I – V curve according to the Simmons equation. The magnetoresistance curves can be divided to high-field MR and low-field MR (LFMR) parts. The former is ascribed to the influence of spin disorder or canting within the LSMO nanoparticle surface and the latter one with strong bias dependence is attributed to the spin-dependent tunneling effect through the insulating surface layer of LSMO and oleic acid molecules. The enhanced LFMR effect for oleic acid coated LSMO with respect to the bare LSMO was attributed to the enhanced tunneling transport and weak spin scattering in oleic acid molecule barrier.

Large area nitrogen (N)-doped graphene films were grown on copper foil by chemical vapor deposition. The as-grown films consisted of a single atomic layer that was continuous across the copper surface steps and grain boundaries, and could be easily transferred to a variety of substrates. N-doping was confirmed by X-ray photoelectron spectroscopy, Raman spectroscopy, and elemental mapping. N atoms were suggested to mainly form a “pyrrolic” nitrogen structure, and the doping level of N reached up to 3.4 at.%. The N-doped graphene exhibited an n-type behavior, and nitrogen doping would open a band gap in the graphene. This study presents use of a new liquid precursor to obtain large area, continuous and mostly single atom layer N-doped graphene films.

A series of (Fe0.67Co0.33)(1-x)Sm-x (0

FeCoNd thin film with thickness of 166 nm has been fabricated on silicon (1 1 1) substrates by magnetron co-sputtering and annealed for one hour under magnetic field at different temperatures (Ta) from 200 °C to 700 °C. The As-deposited and annealed FeCoNd film samples at Ta ≤ 500 °C were amorphous while the ones obtained at Ta ≥ 600 °C were crystallized. We found that the perpendicular anisotropy field gradually decreases as the annealing temperature increases from room temperature to 300 °C. A well induced in-plane uniaxial anisotropy is achieved at the annealing temperature between 400 and 600 °C. The variation of the dynamic magnetic properties of annealed FeCoNd films can be well explained by the Landau–Lifshitz equation with the variation of the anisotropy field re-distribution and the damping constant upon magnetic annealing. The magnetic annealing might be a powerful post treatment method for high frequency application of magnetic thin films.

The magnetic properties of FeNiSm thin films with different thicknesses, different Ta interlayer thicknesses and different numbers of Ta interlayers were investigated. The single layer FeNiSm shows in-plane uniaxial anisotropy at a thickness below critical value, but shows weak perpendicular anisotropy with a stripe domain structure at thickness above the critical value. Experiments indicate that one or more Ta interlayers inserted into thick FeNiSm films with weak perpendicular anisotropy were effective not only in canceling the perpendicular anisotropy, but also in recovering the in-plane uniaxial anisotropy. Blocking of the columnar growth of FeNi grains by the Ta interlayer is considered to be responsible for this spin reorientation phenomenon. Moreover, the magnetization reversal mechanism in FeNiSm films with uniaxial anisotropy can be ascribed to coherent rotation when the applied field is close to the hard axis and to domain-wall unpinning when the applied field is close to the easy axis. The dynamic magnetic properties of FeNiSm films with uniaxial anisotropy were investigated in the frequency range 0.1–5 GHz. The degradation of the soft magnetic properties of magnetic thin films due to the growth of columnar grains can be avoided by insertion of a Ta interlayer.

The microwave absorption properties of nanosized double perovskite Sr 2 FeMoO 6 and epoxy resin composites were investigated in the frequency range of 2–18 GHz using the coaxial method. The Sr 2 FeMoO 6 composites with an optimal 20 wt% epoxy resin showed a strong electromagnetic attenuation of −49.3 dB at 8.58 GHz with a matching thickness of 2.15 mm. Moreover the optimum absorption frequency at which the reflection loss is less than −20 dB, which corresponds to 99% reflection loss of the incident microwave, is from 5.7 to 13.2 GHz with the matching thickness ranging from 3.0 to 1.5 mm. The excellent microwave-absorption properties are a consequence of a proper electromagnetic match due to the existence of the insulating matrix of anti-site defects and anti-phase domains, which not only contribute to the dielectric loss but also to the reduced eddy current loss.

Fe-doped In2O3 powders were prepared using the sol–gel method. Solubility of Fe ions in the In2O3 host compound reached up to 50%. Lattice constant decreased linearly as Fe doping concentration increased, indicating that Fe ions were incorporated into the host lattice and occupied the In sites. Ferromagnetism could be obtained from the samples with carbothermal annealing. The dependence of ferromagnetism on the carbon dosage was observed. The greater the carbon dosage, the higher the concentration of oxygen vacancies (Vo) created, and the more robust the ferromagnetism.

We presented detailed characterizations of the ferromagnetic properties of undoped and Cr-doped SnO 2 nanowires synthesized by chemical vapor deposition. All the samples exhibit room-temperature ferromagnetism. Our experiments reveal that, in addition to the contribution of surface oxygen vacancies, Cr doping into SnO 2 plays an important role in tuning the ferromagnetism of SnO 2 nanostructures. Doping the SnO 2 nanowires with 1.8 at.% Cr enhances the magnetization by 28%. We applied the bound magnetic polaron model to successfully explain the enhancement of ferromagnetism.