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Van der Waals antiferromagnetic and topological insulator materials provide powerful platforms for modern optical, electronic, and spintronic devices applications. The interaction between an antiferromagnet (AFM) and a topological insulator (TI), if sufficiently strong, could offer emergent hybrid material properties that enable new functionality exceeding what is possible in any individual material constituent. In this work, we study strong coupling between THz excitations in a three dimensional (3D) topological insulator and a quasi-two dimensional (2D) antiferromagnetic material resulting in a new hybridized mode, namely a surface Dirac plasmon-phonon-magnon polariton. We find that the interaction between a surface Dirac plasmon polariton in the 3D TI and a magnon polariton in the 2D AFM is mediated by the phonon coupling in the 3D TI material. The coupling of phonons with an electromagnetic wave propagating in the 3D TI enhances the permittivity of the TI thin film in a way that results in a strong correlation between the dispersion of Dirac plasmon polaritons on the surfaces of the TI with the thickness of the TI. As a result, the dispersion of surface Dirac plasmon polaritons in the TI can be tuned toward resonance with the magnon polariton in the AFM material by varying the TI's thickness, thereby enhancing the strength of the coupling between the excitations in the two materials. The strength of this coupling, which results in the surface Dirac plasmon-phonon-magnon polariton, can be parameterized by the amplitude of the avoided-crossing splitting between the two polariton branches at the magnon resonance frequency...

Device surface properties are critical for its performance such as channel electron density, leakage current, subthreshold swing (SS), and noise in gallium nitride high-electron-mobility transistors (HEMTs). In this article, the improved surface property of InAlN/GaN HEMTs with forming gas (FG, 5% H2, and 95% N2) annealing is demonstrated. X-ray photoelectron spectra (XPS) show that the number of Ga–O bonds decreases while that of the Ga–N bonds increases, an indication of the surface native oxide removal after FG annealing. Compared with N2 annealing, an increase of two-dimensional electron gas (2DEG) electron density with FG annealing is determined by both energy band simulation and capacitance–voltage measurement. Transmission line measurement (TLM) shows that N2 annealing offers a lower ohmic contact resistance ( ${R}_{\text {C}}$ ) while FG annealing features a lower sheet resistance ( ${R}_{\text {sheet}}$ ). Herein, a FG/N2 two-step ohmic contact annealing is developed to achieve a SS of 110 mV/dec, a transconductance ( ${g}_{\text {m}}$ ) peak of 415 mS/mm, a record low drain-induced barrier lowing (DIBL) of 65 mV/V, and a record high power gain cutoff frequency ( ${f}_{\text {max}}$ ) of 270 GHz on a 50-nm InAlN/GaN HEMT on Si.

Second-harmonic Hall voltage (SHV) measurement method has been widely used to characterize the strengths of spin–orbit torques (SOTs) in heavy metal/ferromagnet thin films saturated in the single-domain regime. Here, we show that the magnetic anisotropy of a W/Pt/Co trilayer can be robustly tuned from in-plane to out-of-plane by varying W, Pt, or Co thicknesses. Moreover, in samples with easy-cone anisotropy, SHV measurements exhibit anomalous ‘humps’ in the multidomain regime accessed by applying a nearly out-of-plane external magnetic field. These hump features can only be explained as a result of the formation of Néel-type domain walls, efficiently driven by nevertheless small SOTs in this double heavy metal heterostructure with canceling spin Hall angles.

The in situ pyrolysis of metal–organic-frameworks (MOFs) is an effective strategy to prepare magnetic metal nanoparticle (NP) doped porous carbon materials. These composite materials have shown great potential as high performance electromagnetic wave (EMW) absorption materials. So far, the precise control of composite composition and structure has remained a major challenge in constructing highly porous composites with uniformly distributed NPs. In this work, we report a facile route to synthesize tuneable Co NPs embedded in porous nitrogen-doped carbon (Co/NC) nanorods through the direct thermolysis of the bimetal–organic framework (CoZn–ZIF) precursor. By adjusting the proportion of Co2+ in the MOF precursor, the content and distribution of Co NPs in the composite absorber change accordingly. When the molar ratio between Co2+ and Zn2+ is 3 : 1, the carbonized composites exhibit the largest external surface area and the best EMW absorption performance. With a filler mass loading of merely 15 wt%, the minimum reflection loss (RLmin) reaches −52.3 dB at 10.1 GHz with a thin layer thickness of 2.5 mm. The largest effective absorption bandwidth (EAB) of 5.0 GHz (11.1–16.1 GHz) is achieved in a 2.0 mm thick sample. The qualified bandwidth can be up to 14.5 GHz (3.5–18.0 GHz) with the integrated thickness from 1.0 mm to 5.5 mm. The enhanced conductive/magnetic losses, strong interfacial/dipolar/defect polarization, hierarchical pore structure and the geometric effect endow the Co/NC absorber with improved impedance matching and enhanced attenuation of EMW. This work provides a good direction for the future study of MOF-derived lightweight and efficient EMW absorbing materials.

Interfacing topological insulators (TIs) with magnetic insulators (MIs) has been widely used to study the interaction between topological surface states and magnetism. Previous transport studies typically interpret the suppression of weak antilocalization or appearance of the anomalous Hall effect as signatures of magnetic proximity effect (MPE) imposed to TIs. Here, we report the observation of nonlinear planar Hall effect (NPHE) in Bi2Se3 films grown on MI thulium and yttrium iron garnet (TmIG and YIG) substrates, which is an order of magnitude larger than that in Bi2Se3 grown on nonmagnetic gadolinium gallium garnet (GGG) substrate. The nonlinear Hall resistance in TmIG/Bi2Se3 depends linearly on the external magnetic field, while that in YIG/Bi2Se3 exhibits an extra hysteresis loop around zero field. The magnitude of the NPHE is found to scale inversely with carrier density. We speculate the observed NPHE is related to the MPE-induced exchange gap opening and out-of-plane spin textures in the TI surface states, which may be used as an alternative transport signature of the MPE in MI/TI heterostructures.

We have theoretically and experimentally investigated magnetic resonance modes, i.e., optical mode (OM) and acoustic mode (AM), in two coupled ferromagnetic (FM) layers. We calculate the magnetization dynamics of the system by correlating each FM layer via exchange coupling (EC)-induced effective fields. Experimentally, we use CoFe/Ta/NiFe(Cu) trilayers in which the EC is tailored by varying the Ta spacer layer thickness and the saturation magnetization in the (NiFe)1– x Cu x alloy layer. The good agreement between theory and experiment clearly demonstrates that: 1) the resonance frequency of the OM can be significantly higher than that of the individual FM layer; 2) the intensity of the OM can be significantly enhanced by increasing the contrast in the saturation magnetization in two FM layers; and 3) the intensity of the OM, unlike the FMR of a single FM layer, increases with increasing applied magnetic field or frequency. By studying the EC as a function of spacer layer thickness and the saturation magnetization, we further verify that the Neel “orange-peel” coupling is a dominating mechanism in these trilayers, giving rise to coupling between FM layers.

To identify the generation of various contributions in the electrical response of EuTiO3, a series of pure and doped, morphologically different and crystallographically oriented thin films prepared through RF magnetron sputtering and polycrystalline samples prepared through solid state reaction method have been investigated. Effect of stoichiometry, morphology and crystallographic orientation on the electrical response have been traced. Interestingly, in case of thin films, synthesis in more reducing atmosphere led to an in-plane crystallographic re-orientation from [110] to [100], accompanied by the observation of a prominent intrinsic antiferrodistortive phase transition. At temperatures above the antiferrodistorive phase transition, potential barriers to conduction at grain boundary are found to be directly proportional to the oxygen vacancy concentration, and inversely proportional to the average grain size. The relaxation times obtained from the frequency dependent dielectric response show an anomalous non-monotonic variation with temperature, which arises due to the variation of octahedral tilt angle.

Current-independent metal transfer, in free-flight or short-circuiting mode, was previously achieved by utilizing single-side pulsed laser irradiation on the droplet. However, the droplet was always detached with a deflection approximately along the laser incident direction, but not in the wire axial way as generally expected. The droplet deflection also acts as a cushion to the laser impulse. Hence, the double-sided pulsed-laser-driven metal transfer is studied by comparing it with that of non-laser and single laser enhanced metal transfer in this paper. The results demonstrate that double-sided laser irradiation leads to a significant increase in the transfer frequency and process stability. Differing from the way of droplet deflection driven by single laser irradiation, double-sided symmetrical laser irradiation with the same laser pulse parameters results in wire-axial metal transfer of higher frequency, either in drop spray or short-circuiting transfer mode, depending on the arc length. Moreover, the dual laser irradiation contributes considerably to melt the wire when the current is ultra-low. The wire tip was even shaped to a pencil-like profile by the lasers, similar to that of traditional stream spray transfer in high-current GMAW, which facilitates the co-axial metal transfer. The transfer frequency of short-circuiting transfer and drop spray transfer under 80A current is up to100 Hz and 150 Hz (0.8 mm wire diameter, pure argon shielding gas), respectively. Even the current is as low as 40 A, the drop spray transfer frequency can still be up to 100 Hz.

We present a robust technique for computationally studying surface polariton modes in hybrid materials. We use a semi-classical model that allows us to understand the physics behind the interactions between collective excitations of the hybrid system and develop a scattering and transfer matrix method that imposes the proper boundary conditions to solve Maxwell equations and derive a general equation describing the surface polariton in a heterostructure consisting of N constituent materials. We apply this method to a test structure composed of a topological insulator (TI) and an antiferromagnetic material (AFM) to study the resulting surface Dirac plasmon-phonon-magnon polariton (DPPMP). We find that interactions between the excitations of the two constituents result in the formation of hybridized modes and the emergence of avoided-crossing points in the dispersion relations for the DPPMP. For the specific case of a Bi2Se3 TI material, the polariton branch with low frequency below 2 THz redshifts upon increasing the thickness of TI thin film, which leads to an upper bound on the thickness of the TI layer that will allow an observable signature of strong coupling and the emergence of hybridized states. We also find that the strength of the coupling between the TI and the AFM, which is parameterized by the amplitude of the avoided-crossing splitting between the two polariton branches at the magnon resonance frequency, depends on the magnitude of the magnetic dipole and the line width of the magnon in the AFM material as well as on the Fermi energy of Dirac plasmon in the TI. Finally, we predict that materials with extremely high quality, i.e. low scattering loss rate, are essential to achieve an experimentally-observable strong coupling between a TI and AFM., Comment: 16 pages, 12 figures

We demonstrate direct probing of strong magnon–photon coupling using Brillouin light scattering (BLS) spectroscopy in a planar geometry. The magnonic hybrid system comprises a split-ring resonator loaded with epitaxial yttrium iron garnet thin films of 200 nm and 2.46 μm thickness. The BLS measurements are combined with microwave spectroscopy measurements where both biasing magnetic field and microwave excitation frequency are varied. The cooperativity for the 200 nm-thick YIG films is 1.1, and larger cooperativity of 29.1 is found for the 2.46 μm-thick YIG film. We show that BLS is advantageous for probing the magnonic character of magnon–photon polaritons, while microwave absorption is more sensitive to the photonic character of the hybrid excitation. A miniaturized, planar device design is imperative for the potential integration of magnonic hybrid systems in future coherent information technologies, and our results are a first stepping stone in this regard. Furthermore, successfully detecting the magnonic hybrid excitation by BLS is an essential step for the up-conversion of quantum signals from the microwave to the optical regime in hybrid quantum systems.

In addition to the topologically protected linear dispersion, a band-bending-confined two-dimensional electron gas with tunable Rashba spin-splitting (RSS) was found to coexist with the topological surface states on the surface of topological insulators (TIs). Here, we report the observation of large bilinear magnetoresistance (BMR) in Bi2Se3 films decorated with transition metal atoms. The magnitude of the BMR sensitively depends on the type and amount of atoms deposited, with a maximum achieved value close to those of strong Rashba semiconductors. Our first-principles calculations reproduce the quantum well states and reveal sizable RSS in all Bi2Se3 heterostructures with broken inversion symmetry. Our results show that charge-spin interconversion through RSS states in TIs can be fine-tuned through surface atom deposition and easily detected via BMR for potential spintronic applications., Comment: Typos in Fig. 4 caption and Ref. [27] were corrected in this version

This paper reports on the demonstration of microwave power performance at 30 GHz on InAlN/GaN metal–insulator–semiconductor high electron mobility transistor (MISHEMT) on silicon substrate by using the Hf0.5Zr0.5O2 (HZO) as a gate dielectric. Compared with Schottky gate HEMT, the MISHEMT with a gate length (L G) of 50 nm presents a significantly enhanced performance with an ON/OFF current ratio (I ON/I OFF) of 9.3 × 107, a subthreshold swing of 130 mV dec−1, a low drain-induced barrier lowing of 45 mV V−1, and a breakdown voltage of 35 V. RF characterizations reveal a current gain cutoff frequency (f T) of 155 GHz and a maximum oscillation frequency (f max) of 250 GHz, resulting in high (f T × f max)1/2 of 197 GHz and the record high Johnson’s figure-of-merit (JFOM = f T × BV) of 5.4 THz V among the reported GaN MISHEMTs on Si. The power performance at 30 GHz exhibits a maximum output power of 1.36 W mm−1, a maximum power gain of 12.3 dB, and a peak power-added efficiency of 21%, demonstrating the great potential of HZO/InAlN/GaN MISHEMTs for the Ka-band application.

With the realization of stress-induced perpendicular magnetic anisotropy, efficient spin-orbit torque switching, and room temperature topological Hall effect, interest in rare earth iron garnets has been revived in recent years for their potential in spintronic applications. In this study, we investigate the magnetic properties of micrometer-thick Bi and Ga substituted thulium iron garnets (BiGa:TmIG) grown by the liquid-phase epitaxy method. Above the magnetization compensation (MC) temperature, anomalous triple hysteresis is observed in BiGa:TmIG/Pt heterostructures by anomalous Hall effect measurements. X-ray magnetic circular dichroism and energy dispersive spectroscopy measurements reveal its origin as an internal exchange bias (EB) effect arising from inhomogeneities localized at the surface of the film. Possibly depending on the difference in thickness and defect realization of the EB layer, two types of magnetization reversal mechanisms, namely, the Stoner-Wohlfarth type and the reversible domain-wall motion type, are observed. Our results show that rich meta-magnetic phases exist in garnets close to MC, which can be robustly tuned by chemical composition engineering and conveniently probed by electrical transport measurements.

Ordered Co-Ni core-shell magnetic nanorod arrays were fabricated by a two-step electrodeposition into a self-assembled anodic alumina oxide template. The characterizations of the morphology and elemental distribution indicated the successful fabrication of ∼260 nm Co core nanorods surrounded by ∼20 nm concentric Ni shell. The magnetization measurement revealed that the synthesized Co-Ni core-shell nanorod arrays exhibited lower coercivity and higher remanence ratio than plain Co nanorod arrays, offering a possibility to regulate suitable coercivity at the nanoscale. It was also demonstrated combing tube and rod to form core-shell structure offered the perspective for engineering the magnetic properties without changing geometric parameters or with minimally altered crystalline structure.

Magnetic nanowire arrays grown in anodized alumina templates offer a fertile ground to investigate the interplay among the exchange interaction, dipolar interaction, and magnetocrystalline anisotropy. In this study, we have successfully fabricated Co nanowire arrays with gradient diameter while maintaining the nanowire separation. Consequently, we are able to obtain nanowire arrays with dominant exchange interaction at one end with small nanowire dimeter and dominant dipolar interaction at the other with large nanowire diameter. These samples show very different magnetic properties from those observed in magnetic nanowire arrays with uniformly diameter. The easy magnetization axis, coercivity, saturation field, and reversal processes are all controlled collectively by both ends of the nanowires, which cannot be viewed as the combination of magnetic nanowire arrays with thin and thick diameters.

We demonstrate simultaneous detection of current-driven dampinglike and fieldlike spin–orbit torques in heavy metal/ferromagnetic metal bilayers by measuring all three magnetization components $m_{x},m_{y}$ , and $m_{z} $ using a vector-resolved magnetooptic Kerr effect (MOKE) technique based on quadrant detection. We investigate the magnitude and direction of spin–orbit torques in a series of platinum/permalloy samples, finding good agreement with results obtained via polar and quadratic MOKE measurements without quadrant detection.

In the field of electrochemical CO2 conversion, the development of earth-abundant catalysts which are selective for a single product is a central challenge. Cu-Sn bimetallic catalysts have been reported to yield selective CO2 reduction towards either carbon monoxide or formate. To advance the understanding of possible synergetic effects between Cu and Sn which direct product selectivity, a thorough investigation of the catalyst structure and composition in its active state is desired. We present an X-ray spectroscopy investigation of oxide-derived Cu-Sn catalysts prepared by functionalization of Cu(OH)2 nanowire arrays with ultrathin SnO2 overlayers. This method allows precisely tunable Sn composition, which enables synthesis of composite catalysts with high selectivity toward either CO or formate. Under CO2 reduction conditions, the materials undergo significant transformations before reaching their catalytically active forms. Complementary information on the electrocatalysts’ dynamic bulk and surface structure was revealed via correlating observations from multiple X-ray spectroscopy methods. In situ investigations of Cu K-edge revealed that in the bulk Cu is fully reduced from Cu2+ to Cu° after a pre reduction step. Quasi in situ XPS demonstrated that, at the catalyst surface, Cu is also present exclusively as Cu°, whereas significant differences in Sn quantification and speciation were observed between the CO- and formate-selective catalysts. After CO2 electrolysis, CO-selective catalysts exhibited a surface Sn content of 13 at. % predominantly present as Sn oxide, while the formate-selective catalysts had a Sn content of ~70 at. % consisting of both metallic Sn° and Sn oxide species. Our study reveals the complex dependence of catalyst structure, composition, and speciation with applied electrochemical bias in Sn-functionalized nanostructured Cu catalysts.

Nanowire arrays can be conveniently fabricated by electrodeposition methods using porous anodized alumina oxide templates. They have found applications in numerous fields. Nanotube arrays, with their hollow structure and much enhanced surface-to-volume ratio, as well as an additional tuning parameter in tube wall thickness, promise additional functions compared with nanowire arrays. Using a similar fabrication method, we have developed a facile and general method to fabricate metallic nanotubes (NTs). Using Ni NTs as a model system, the mechanism of the hydrogen-assisted NT growth was postulated and confirmed by controlling the hydrogen formation with conductive salts in an electrodeposition solution, which improves the H2 concentration but prevents the large H2 bubbles from blocking the nanochannel of a template. The controlled hydrogen generation forces the growth along the wall of nanochannels in the templates, leading to the NT formation. The magnetic properties can be controlled by the NT wall thickness, making these NTs useful for various applications.

Van der Waals (vdW) material Fe5GeTe2, with its long-range ferromagnetic ordering near room temperature, has significant potential to become an enabling platform for implementing novel spintronic and quantum devices. To pave the way for applications, it is crucial to determine the magnetic properties when the thickness of Fe5GeTe2 reaches the few-layers regime. However, this is highly challenging due to the need for a characterization technique that is local, highly sensitive, artifact-free, and operational with minimal fabrication. Prior studies have indicated that Curie temperature T C can reach up to close to room temperature for exfoliated Fe5GeTe2 flakes, as measured via electrical transport; there is a need to validate these results with a measurement that reveals magnetism more directly. In this work, we investigate the magnetic properties of exfoliated thin flakes of vdW magnet Fe5GeTe2 via quantum magnetic imaging technique based on nitrogen vacancy centers in diamond. Through imaging the stray fields, we confirm room-temperature magnetic order in Fe5GeTe2 thin flakes with thickness down to 7 units cell. The stray field patterns and their response to magnetizing fields with different polarities is consistent with previously reported perpendicular easy-axis anisotropy. Furthermore, we perform imaging at different temperatures and determine the Curie temperature of the flakes at ≈300 K. These results provide the basis for realizing a room-temperature monolayer ferromagnet with Fe5GeTe2. This work also demonstrates that the imaging technique enables rapid screening of multiple flakes simultaneously as well as time-resolved imaging for monitoring time-dependent magnetic behaviors, thereby paving the way towards high throughput characterization of potential two-dimensional (2D) magnets near room temperature and providing critical insights into the evolution of domain behaviors in 2D magnets due to degradation.

In recent years, nonreciprocal transport measurement has emerged as a probe of spin orbit interaction, spin texture, superconductivity, and other fundamental properties of materials. Here, we study the nonlinear Hall effect (NLHE) in ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}/\mathrm{CoFeB}$ heterostructures measured by second harmonic voltage method. Magneto-optical Kerr effect measurements demonstrate the origin of the NLHE to be the asymmetric magnon scattering mechanism. Moreover, a linear relation between the nonlinear Hall resistance and the electron phase coherence length of ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ is observed between 5 and 50 K. We propose a phenomenological model that explains the enhancement of the NLHE below 50 K as a result of one-dimensional antilocalization of electrons from spin disorder, enabled by spin-momentum locking and conservation of angular momentum.

Spin-orbit coupling (SOC) can convert a charge current into a spin current, enabling electrical control of magnetization, the foundation of spintronic devices. A quintessential example of SOC-induced transport in a ferromagnetic conductor (FM) is the anomalous Hall effect (AHE), in which an electric current perpendicular to the magnetization generates a transverse spin current and charge accumulations on the surface. Applying similar considerations to the configuration of a current parallel to the magnetization, SOC should also give rise to a transverse spin current with spins orthogonal to both the magnetization and spin current. The transverse spins precess rapidly about the magnetization direction and exert torque on the magnetization as they dephase, in analogy with spin transfer torque. In this talk, we will discuss this transverse spin Hall effect (TSHE) leads to anomalous spin-orbit torque (ASOT) on the top and bottom surfaces of a FM. In addition, we will also discuss the

An ultrafast vector magneto-optical Kerr effect (MOKE) microscope with integrated time-synchronized electrical pulses, two-dimensional magnetic fields, and low-temperature capabilities is reported. The broad range of capabilities of this instrument allows the comprehensive study of spin-orbital interaction-driven magnetization dynamics in a variety of novel magnetic materials or heterostructures: (1) electrical-pump and optical-probe spectroscopy allows the study of current-driven magnetization dynamics in the time domain, (2) two-dimensional magnetic fields along with the vector MOKE microscope allow the thorough study of the spin-orbital-interaction induced magnetization re-orientation in arbitrary directions, and (3) the low-temperature capability allows us to explore novel materials/devices where emergent phenomena appear at low temperature. We discuss the details and challenges of this instrument development and integration and present two datasets that demonstrate and benchmark the capabilities of this instrument: (a) a room-temperature time-domain study of current-induced magnetization dynamics in a ferromagnet/heavy metal bilayer and (b) a low-temperature quasi-static polar MOKE study of the magnetization of a novel compensated ferrimagnet.

We report on the electrical detection of a hybrid magnon-photon system, which is comprised of a magnetic sample coupled to a planar cavity. While the uniform Kittel mode has the largest coupling strength among all the magnon modes, it only generates a modest voltage signal by means of inverse spin-Hall effect. We have found that the generated voltage can be significantly enhanced by introducing a higher order magnon mode, which possesses a much higher spin pumping efficiency and furthermore, it is nearly degenerated with the Kittel mode. The experimental results can be explained by our theoretical model, and suggest that the use of an auxiliary magnon mode can realize the configuration of a magnon-photon system with both strong coupling and large spin current.

Absract The central unit in an integrated memory device is a magnetic tunnel junction (MTJ) consisting of two ferromagnetic layers, often using complex alloys such as CoFeB, separated by an insulating barrier such as MgO. Atomic level precision is required to miniaturize these components, and atomic layer etching (ALE) is one of the most promising methods to do this. However, at the nanoscale, it is imperative to maintain the concentration of each element in an alloy during etching, and it is important to not affect the insulating barrier, i.e. the etching process should stop at MgO. Here we use thermal dry etching of CoFeB alloy thin films with sequential doses of chlorine and 2,4-pentanedione (acetylacetone, acacH). Patterned samples are modified with atomic level precision, and the process is completely selective to the removal of CoFeB alloy in ALE regime without changing the alloy composition and without etching MgO that is used as a protecting layer. The etching process was investigating by comparing the film thickness on a patterned surface before and after ALE process using atomic force microscopy (AFM). The viable key features of the reaction mechanism were proposed following by detection of key desorbing fragments during a heating ramp via temperature-programmed desorption (TPD) experiments. Ex-situ X-ray photoelectron spectroscopy (XPS) was performed to characterize the surface during ALE process.

High reflection loss, wide bandwidth and low density are desirable attributes of electromagnetic wave absorption materials. Here, an ultra-thin MnO2/Fe3O4/carbon nanotube film has been synthesized in two steps using solvothermal deposition and electrochemical deposition. The Fe3O4 nanoparticles and the MnO2 sheets form a nano-scale core-shell structure on the surface of the carbon nanotube film. A series of this hierarchical composite film with different shell structures and MnO2 weight ratios were successfully synthesized. Their unique micro-structure greatly enhances the electromagnetic wave absorption capability of the composites. Instrinsic ferromagnetism is confirmed by the magnetic hysteresis loops. The strong couplings among dielectric loss, hysteresis loss and multiple scattering resulted in the reflection loss up to −42.2 dB with the bandwidth of 7.1 GHz at 10% MnO2 weight ratio for a flexible composite film of 1 mm thick.

Modification of various properties of graphene oxide (GO) films on SiO2/Si substrate under KrF laser radiation was extensively studied. X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and the electrical resistance measurements were employed to correlate the effects of laser irradiation on structural, chemical and electrical properties of GO films under different laser fluences. Raman spectroscopy shows reduced graphene oxide patterns with increased I2D/IG ratios in irradiated samples. X-ray photoelectron spectroscopy shows a high ratio of carbon to oxygen atoms in the reduced graphene oxide (rGO) films compared to the pristine GO films. X-ray diffraction patterns display a significant drop in the diffraction peak intensity after laser irradiation. Finally, the electrical resistance of irradiated GO films reduced by about four orders of magnitudes compared to the unirradiated GO films. Simultaneously, reduction and patterning of GO films display promising fabrication technique that can be useful for many graphene-based devices.

The spin–orbit interaction enables interconversion between a charge current and a spin current. It is usually believed that in a nonmagnetic metal (NM) or at a NM/ferromagnetic metal (FM) bilayer interface, the symmetry of spin–orbit effects requires that the spin current, charge current, and spin orientation are all orthogonal to each other. Here we demonstrate the presence of spin–orbit effects near the NM/FM interface that exhibit a very different symmetry, hereafter referred to as spin-rotation symmetry, from the conventional spin Hall effect while the spin polarization is rotating about the magnetization. These results imply that a perpendicularly polarized spin current can be generated with an in-plane charge current simply by use of a FM/NM bilayer with magnetization collinear to the charge current. The ability to generate a spin current with arbitrary polarization using typical magnetic materials will benefit the development of magnetic memories., Converting charge to spin currents using spin–orbit interactions has useful applications in spintronics but symmetry constraints can limit the control over spin polarization. Here the authors demonstrate spin–orbit effects with a different symmetry, which could help generate arbitrary spin polarizations.

Spin Seebeck effect (SSE) measured for metallic ferromagnetic thin films in commonly used longitudinal configuration contains the contribution from anomalous Nernst effect (ANE). The ANE is considered to arise from the bulk of the ferromagnet (FM) and the proximity-induced FM boundary layer. We fabricate a FM alloy with zero Nernst coefficient to mitigate the ANE contamination of SSE and insert a thin layer of Cu to separate the heavy metal (HM) from the FM to avoid the proximity contribution. These modifications to the experiment should permit complete isolation of SSE from ANE in the longitudinal configuration. However, further thickness dependence studies and careful analysis of the results revealed, ANE contribution of the isolated FM alloy is twofold, surface and bulk. Both surface and bulk contributions, whose magnitudes are comparable to that of the SSE, can be modified by the neighboring layer. Hence surface contribution to the ANE in FM metals is an important effect that needs to be considered.

AbstarctGraphene has sparked extensive research interest for its excellent physical properties and its unique potential for application in absorption of electromagnetic waves. However, the processing of stable large-scale graphene and magnetic particles on a micrometer-thick conductive support is a formidable challenge for achieving high reflection loss and impedance matching between the absorber and free space. Herein, a novel and simple approach for the processing of a CNT film-Fe3O4-large scale graphene composite is studied. The Fe3O4 particles with size in the range of 20–200 nm are uniformly aligned along the axial direction of the CNTs. The composite exhibits exceptionally high wave absorption capacity even at a very low thickness. Minimum reflection loss of −44.7 dB and absorbing bandwidth of 4.7 GHz at −10 dB are achieved in composites with one-layer graphene in six-layer CNT film-Fe3O4 prepared from 0.04 M FeCl3. Microstructural and theoretical studies of the wave-absorbing mechanism reveal a unique Debye dipolar relaxation with an Eddy current effect in the absorbing bandwidth.

Nanometer-thick Y 3 Fe 5 O 12 (YIG) films with very low damping constant have been fabricated on gadolinium gallium garnet substrates using chemical metal-organic decomposition method. Both the microstructure and ferromagnetic properties of the YIG thin films have been studied. High resolution X-ray diffraction result displayed an epitaxial structure of the YIG film. Surface morphology was investigated using an atomic force microscopy. The average surface roughness is about 0.8 ± 0.2 nm for a ∼50 nm thick epitaxial growth YIG film, which is comparable to the result of pulse laser deposition grown films. The coercivity field of the YIG film is around 1.5 Oe. Furthermore, magnetization dynamics properties were studied using a coplanar waveguide vector-network-analyzer ferromagnetic resonance spectrometer. The extracted damping constant is as low as 1.4 × 10 −3 . The results show that high quality nanometer YIG films can be obtained through chemical epitaxial growth method. It would be very useful for the garnet based spintronics applications.

We use time-resolved (TR) measurements based on the polar magneto-optical Kerr effect (MOKE) to study the magnetization dynamics excited by spin orbit torques in Py (Permalloy)/Pt and Ta/CoFeB bilayers. The analysis reveals that the field-like (FL) spin orbit torque (SOT) dominates the amplitude of the first oscillation cycle of the magnetization precession and the damping-like (DL) torque determines the final steady-state magnetization. In our bilayer samples, we have extracted the effective fields, hFL and hDL, of the two SOTs from the time-resolved magnetization oscillation spectrum. The extracted values are in good agreement with those extracted from time-integrated DCMOKE measurements, suggesting that the SOTs do not change at high frequencies. We also find that the amplitude ratio of the first oscillation to steady state is linearly proportional to the ratio hFL/hDL. The first oscillation amplitude is inversely proportional to, whereas the steady state value is independent of, the applied external field along the current direction., 12 pages, 4 figures

The correlation between the magnetocaloric effect and magnetotransport property was investigated in Ni

Spin-orbit interaction (SOI) couples charge and spin transport, enabling electrical control of magnetization. A quintessential example of SOI-induced transport is the anomalous Hall effect (AHE), first observed in 1880, in which an electric current perpendicular to the magnetization in a magnetic film generates charge accumulation on the surfaces. Here we report the observation of a counterpart of the AHE that we term the anomalous spin-orbit torque (ASOT), wherein an electric current parallel to the magnetization generates opposite spin-orbit torques on the surfaces of the magnetic film. We interpret the ASOT as due to a spin-Hall-like current generated with an efficiency of 0.053+/-0.003 in Ni80Fe20, comparable to the spin Hall angle of Pt. Similar effects are also observed in other common ferromagnetic metals, including Co, Ni, and Fe. First principles calculations corroborate the order of magnitude of the measured values. This work suggests that a strong spin current with spin polarization transverse to magnetization can exist in a ferromagnet, despite spin dephasing. It challenges the current understanding of spin-orbit torque in magnetic/nonmagnetic bilayers, in which the charge-spin conversion in the magnetic layer has been largely neglected., 23 pages, 3 figures and 1 table

It is challenge to quantitatively determine the spin Seebeck effect (SSE) of ferromagnetic metals (FM) due to many other thermoelectric signals including the anomalous Nernst effect (ANE), magnetic proximity-induced ANE, and inverse spin Hall effect (ISHE) in FM. By comparing the thermoelectric signals of single FM layer and FM/Pt bilayer and model-assisted analyses of ISHE contribution in FM, we are able to determine the pure SSE signals and the spin Seebeck coefficients of Fe, Co, Ni, and Ni80Fe20 over a temperature range from 90 to 300 K. The spin-dependent Seebeck coefficients S ↑ and S ↓ , which is related to the density of states of FM, were also determined experimentally by combining the conventional Seebeck coefficient and the SSE coefficient. We further suggest the calculation of the SSE coefficient should include the spin-dependent conductivities via S s ≡ σ ↑ S ↑ - σ ↓ S ↓ σ ↑ + σ ↓ .

Advanced permanent magnets based on rare-earth-free MnBi intermetallic alloys are considered energy-critical materials due to their applications in high temperature power electronics and green energy-related generators and motors, owing to their positive temperature coefficient of magnetic anisotropy. However, a direct method to achieve high saturation magnetization, without the significant loss of coercivity, is critical for attaining high performance MnBi magnets. Here, we demonstrate the synthesis and processing of magnetic nanocomposites, consisting of metal-redox MnBi nanoparticles and electro-spun FeCo nanowires. The composition ratio, processing dependent magnetism, and increased coercivity with increasing temperature, were studied in MnBi-FeCo nanocomposites. The magnetic performance of nanocomposites was dictated by interfacial coupling between magnetically hard MnBi and semi-hard FeCo nanowires, as well as the composition ratio and processing conditions. Solution processed MnBi-FeCo nanocomposites allow the potential for the development of high temperature and high performance rare-earth-free permanent magnets.

A systematic study of the electrodynamic coupling between the ferromagnetic resonance (FMR) and the cavity mode of a microwave cavity is presented. The nature of the FMR and cavity modes, described by their resonance position and line width, is measured and compared with a classical model based on the Landau–Lifshitz–Gilbert equation and an RLC circuit, which explicitly implement Faraday’s and Ampere’s laws. The relationship between the coupling gap, which can be accessed experimentally, and the coupling strength, which is a fundamental property of the FMR/cavity system, is discussed on the basis of this model. A straightforward method is experimentally developed to control the coupling gap. The capability of using such a tunable cavity-FMR coupling in combination with spin pumping could provide us with new technologies that utilize the light-matter interaction to control spin current in cavity spintronics.

We experimentally measured the fieldlike spin–orbit torque (SOT) by the second-order planar Hall effect, as well as the dampinglike SOT by the polar magnetooptic Kerr effect in NiFe(1.5 nm)/AuCu( $x$ nm) bilayers with $2~\textrm {nm} \le x \le 8$ nm. We found that the spin diffusion length in the Au–Cu alloy is $\sim 5$ nm, which is shorter than that of pure Au and Cu. When the thickness of the AuCu layer is above the spin diffusion length, the spin Hall angle of the Au–Cu alloy is $\sim 1.3\pm 0.2$ %, which is much larger than that of pure Cu and Au. The results imply that large spin Hall angle materials can be explored in the nonmagnetic alloys of constituent elements having weak or negligible spin–orbit coupling.

Single crystal Fe nanowires have been successfully synthesized by chemical vapor deposition process at 600 °C using ferrocene as precursor and sapphire substrate with self-assembled Au nanoparticle catalyst. The growth mechanism of Fe nanowires has been investigated. At 600 °C, ferrocene decomposes into Fe which subsequently alloy with Au nanoparticles on the substrate. Fe–Au alloy nanoparticles act as nucleus sites for the growth of single crystal Fe nanowire. The competition between magnetocrystalline anisotropy and shape anisotropy leads to an easy magnetization axis along the wire direction, but with a small remanent magnetization.