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We report a technique to realize reconfigurable colloidal crystals by using the controlled motion of particle defects above an externally modulated magnetic substrate. The transport of particles is induced by applying a uniform rotating magnetic field to a ferrite garnet film characterized by a periodic lattice of magnetic bubbles. For filling factor larger than one colloid per bubble domain, the particle current arises from propagating defects where particles synchronously exchange their position when passing from one occupied domain to the next. The amplitude of an applied alternating magnetic field can be used to displace the excess particles via a swapping mechanism, or to mobilize the entire colloidal system at a predefined speed. [ABSTRACT FROM AUTHOR]

Nonreciprocity has become a research hotspot in the field of thermal radiation. Nonetheless, the majority of current nonreciprocal thermal radiation is confined to TM polarization. This paper introduces a two-dimensional nanograting structure exhibiting strong dual-polarization nonreciprocal thermal radiation. The grating is composed of a GaAs-based periodic nanoarray, a magneto-optic medium layer (InAs), and a metallic reflective layer (Al). The impact of nonreciprocity under different polarizations was investigated using rigorous coupled-wave analysis. Additionally, the magnetic field energy distribution was studied, and an explanation for the observed phenomenon of the device's nonreciprocal thermal radiation was given for both TE and TM polarizations. The present study is expected to contribute insights for the study of nonreciprocal thermal radiation. [ABSTRACT FROM AUTHOR]

Optical switches in metal–dielectric–metal (MIM) structures attracted much interest for chip-scale plasmonic modulator merging nanoelectronics and ultrafast photonics. The absorption switches employed gain modulations; thus, their switching speed is limited to the sub-gigahertz range because of the spontaneous lifetime of the transition. In this paper, we theoretically predicted that the function of the absorption switches is achieved employing magnetic field reversal and constant gain instead of gain modulations. We investigated analytically and numerically transmission in the presence of both gain and gyration and revealed that the transmission shift by the external magnetic field is maximized at a resonance value of gain. The switching speed can reach the THz range thanks to the large optical bandwidth in the MIM stub structures and the advanced magnetization switching technology. The MIM structure with combined gain and magnetoplasmonic properties enhances interaction between light and magnetic field on nanoscale and enables the device footprint down to the deep subwavelength scale λ 2 / 50. [ABSTRACT FROM AUTHOR]

Magnetic sensors with high sensitivity are critical for various technological applications. This paper presents a highly sensitive magnetic sensor based on magnetic torque. The sensor comprises a silicon cantilever with a micro-pillared soft magnet at its end. A piezoresistive strain sensing element is integrated into the silicon cantilever for detecting vibration signals. The prototype of the resonant magnetic sensor is designed, fabricated, and evaluated. When an alternating magnetic field, generated by a coil, is applied to the cantilever, the micro-pillared magnet undergoes pendulum-like vibrations due to magnetic torque. Additionally, the application of the alternating magnetic field, which causes the external magnetic field to change the effective spring constant of the silicon cantilever, results in a change in resonant frequency. The evaluation results demonstrate that the fabricated magnetic sensor achieves a maximum sensitivity of 114.02 Hz/mT and a minimum detectable magnetic field of 35.7 nT. These findings suggest the sensor's potential for high-sensitivity magnetic field measurements in various applications. [ABSTRACT FROM AUTHOR]

A phase transformation model based on magnetization is proposed in this paper, which accurately tracks the change in the phase transformation volume fraction with time/temperature f-T/t by analyzing phase transformation magnetization curves under a magnetic field. This allows for the determination of kinetic parameters related to the nucleation and growth processes such as the phase transformation rate df/dt-T/t and Avrami exponent n, enabling quantitative analysis of phase transformation kinetics under magnetic field effects. Additionally, the phase transformation magnetization under a magnetic field can be accurately fitted by combining the volume fraction calculation model with the Johnson–Mehl–Avrami equation, thus also obtaining the kinetics parameters. The aforementioned two models are applied to study the isothermal and isokinetic transformations of austenite (γ) to ferrite (α) in Fe-1 wt. %Cu alloys, demonstrating the effects of external conditions through variations in kinetic parameters. [ABSTRACT FROM AUTHOR]

In this paper, we have measured the magneto-optical spin Hall effect influenced by an arbitrary oriented magnetic field using CeDyAl thin films on Gd3Ga5O12 (GGG) substrates as reflective materials. Plots of the variation of the magneto-optic spin Hall effect (MOPSHE) with magnetic field strength, the hysteresis line, in three different unit-direction magnetic fields are simulated and experimentally measured. The comparison of the simulation results with the experiments allows the method of weak measurement to determine the MOPSHE under the influence of the magnetic field to be validated. MOPSHE under a three-dimensional magnetic field is measured and the measurement error is within 4 μ m. [ABSTRACT FROM AUTHOR]

This paper presents a systematic study of the charge transport behavior of heavily doped n-type Ge layers with As and Sb. A nonequilibrium method ion implantation followed by milliseconds flash lamp annealing is applied to synthesize the n++ Ge layers (Ge:As and Ge:Sb). The resulting materials contain free electrons with a density above 3 × 1019 cm−3 and mobility more than 220 cm2/(V s). Quantum corrections to the conductance in a magnetic field are observed at low temperatures. Weak localization persists up to 30 K in Ge:Sb, while only up to 10 K in Ge:As. Using the Hikami–Larkin–Nagaoka model to fit the magnetoconductance data, we obtain the phase coherence length l ϕ of the hyperdoped Ge samples in the range of 70–163 nm. This study may pave a way to explore possible applications for quantum technologies utilizing As- and Sb-hyperdoped Ge. [ABSTRACT FROM AUTHOR]

The Hull cutoff represents the maximum magnetic field in a vacuum crossed-field gap (CFG) such that an electron emitted from the cathode reaches the anode. Prior studies demonstrated that introducing ions into a CFG always causes increased excursion of electrons toward the anode. In this paper, we assess a collisional CFG by incorporating collision frequency into the electron force law. The theoretical electron trajectories agree well with a one-dimensional particle-in-cell simulation and demonstrate that emitted electrons always cross a collisional CFG. We derive a modified Hull cutoff condition for a collisional CFG corresponding to an electron reaching the anode with zero velocity in the direction of the electric field. Rather than representing the threshold for magnetic insulation, this condition gives the maximum magnetic field and maximum collision frequency for which an electron reaches the anode without turning around; higher magnetic fields and/or collision frequencies cause the electron to turn around before crossing the gap. Further increasing either quantity causes the electron to change direction more frequently as it crosses the gap, noticeably increasing the transit time with each change in electron direction. In the limit of high collision frequency, the electron velocity across the gap approaches a constant, meaning that electrons will reach the anode at nonzero velocity. The transit time above this condition increases smoothly and monotonically with increasing magnetic field or collision frequency. These results elucidate the implications of collisions on magnetic insulation for future assessments of the limiting current in a collisional CFG. [ABSTRACT FROM AUTHOR]

The photonic spin Hall effect (PSHE) is analogous to the electronic spin Hall effect, which has substantial potential for optoelectronic applications. However, PSHE-based devices are rarely studied, and manipulating the PSHE by charge current has remained elusive thus far. In this paper, we demonstrate current-induced switching of PSHE in the Ce1Dy2Al0.42Fe4.58O12 thin film capping with Pt electrodes, which is mediated by spin–orbit torques at the Pt/Ce1Dy2Al0.42Fe4.58O12 interface. The results show that the transverse beam shifts related to the PSHE can be reversed by applying a small order of magnitude charge current (∼108 A·m−2) to the Pt layer in opposite directions, which predicts low dissipation in our proposed heterostructure. In addition, by applying an in-plane magnetic field, the saturation beam shifts can be increased, which can significantly enhance the switching ratio. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a design concept for a spin-torque nano-oscillator capable of generating spin-wave (SW) packets using magnetic droplets tuned by an electric field (E-field). A comparison is made between this device concept and a conventional setup, where SWs are generated by an oscillating external magnetic field, revealing similar results. The design incorporates a CoFeB layer with perpendicular magnetic anisotropy, acting as a waveguide for propagating SW packets. Adjusting the pulse width of applied E-fields leads to observable changes in the amplitude and periodicity of SW packets. Additionally, this study explores the potential of encoding SW packets as binary signals ("0" and "1"). The findings offer valuable insights into the applications of magnetic droplets and electric-field tuning for spin-wave packet generation, with potential implications for various spintronic devices and technologies. [ABSTRACT FROM AUTHOR]

As the Abrikosov vortex lattice has recently been found in van der Waals heterostructures constructed by a two-dimensional (2D) ferromagnet and a superconductor, we propose the realization of cavity-photon–vortex coupling in a superconductive cavity to construct a new hybrid quantum system in this paper. We study the corresponding hybrid states therein, including the exceptional lines (ELs) in the parameter space. Considering that the parameters of our system are adjustable by external magnetic field and temperature, our system and the ELs are much easier to be realized in experiments. Furthermore, the numerical results show that the corresponding hybrid states can be switched by tuning the source of AC, which makes this hybrid system more advantageous to realize hybrid quantum computing in the future. Moreover, for practical use in detecting hybrid states and the vortex dynamics, the transmission amplitude of an external transverse electric wave through the cavity is also studied. [ABSTRACT FROM AUTHOR]

High-sensitivity MEMS magnetoresistive (MR) sensors have attracted ever-increasing attention due to their ability to detect weak magnetic fields, but the resolution is severely limited by the 1 / f noise. This paper reports a MEMS MR sensor that can effectively suppress the 1 / f noise by modulating the magnetic field signal to the higher frequency region utilizing magnetic tunnel junction vertical motion modulation based on the MEMS piezoelectric cantilever resonator. The magnetic sensitivity can be increased to 2283.3%/mT with a high magnetic gain of 39.3 by integrating the structure-optimized fixed magnetic flux concentrators. The signal-to-noise ratio of the MEMS MR sensor can be improved by three orders of magnitude and the 160 pT/√Hz resolution can be reached. These results make the MEMS MR sensor based on the MTJ motion modulation a competitive candidate in the pico-Tesla magnetic detection. [ABSTRACT FROM AUTHOR]

To achieve omnidirectional wireless power transfer (WPT) with high efficiency, a high Q-factor transmitter generating homogeneous magnetic field is crucial. Traditionally, orthogonal coils of different shapes are used to realize transmitters. In this paper, we develop an omnidirectional magnetic resonant WPT system based on a dielectric disk resonator with colossal permittivity and low loss operating at the axial magnetic quadrupole mode. The constant power transfer efficiency of 88% at the frequency of 157 MHz over the transfer distance of 3 cm for all azimuth angles of a receiver is experimentally demonstrated. The possibility of multi-receivers charging is also studied demonstrating a total efficiency of 90% regardless of azimuth angle between two receivers with respect to the transmitting disk resonator. The minimized exposure of biological tissues to the electric and magnetic fields as well as a low specific absorption rate is observed that makes the WPT system safer for charging with higher input power. [ABSTRACT FROM AUTHOR]

Chirality of antiferromagnetic spin waves as an intrinsic degree of freedom has been attracting considerable attention due to its potential applications for magnonic devices. In this paper, atomistic-scale dynamics simulations were conducted to investigate the chirality of spin wave resonant modes in ferrimagnetic alloy GdxFe1−x (0 < x <1) under different proportion x and external magnetic fields near the angular momentum compensation point. Simulation results reveal that as the proportion of Gd increases, the resonance mode of spin waves undergoes two distinct handedness flipping at magnetization compensation point and angular momentum compensation point. When the proportion x deviates from the magnetization compensation point, a frequency degeneracy point emerges at a non-zero magnetic field, indicating that the chirality of spin waves can also be switched by an external magnetic field. A theoretical analysis is developed to explain the observed phenomena. These findings provide valuable insights into the control and manipulation of spin wave chirality in ferrimagnetic alloys, with potential implications for the development of spin-based devices and technologies. [ABSTRACT FROM AUTHOR]

Direct studies of the adiabatic temperature change (ΔTad) in the Ni47Mn40Sn12.5Cu0.5 Heusler alloy in steady magnetic fields up to 8 T by the extraction method and in pulsed magnetic fields up to 50 T were carried out in this paper. The alloy Ni47Mn40Sn12.5Cu0.5 demonstrates a magnetostructural phase transition (MSPT) of the first order in the 254–283 K temperature range as well as a second order phase transition near the Curie temperature TC = 313 K. An inverse magnetocaloric effect (MCE) was found in the region of the MSPT, and it reaches the maximum value ΔTad = −12 K in 20 T at the initial temperature T0 = 275 K. The irreversible part of the MCE reached ΔTir = −10 K when the field is completely removed. We consider the dynamics of the MCE in the vicinity of the MSPT and discuss the mechanisms that cause the giant irreversibility of the MCE as well as the possibilities of its application in hybrid cooling systems. [ABSTRACT FROM AUTHOR]

Synthetic antiferromagnet (SyAF) has been demonstrated to be an ideal candidate for spin–orbit torque (SOT) based spintronic devices. However, the detailed mechanism needs to be clarified due to the coexistence of multiple effects. This paper studies SOT and the thermoelectric effect in SyAF of Pt/Co/Ru/Co/Pt by harmonic Hall resistance measurements. Different from the traditional Co/Pt bilayers, the second harmonic Hall resistance signals of the SyAF-based devices are obviously enhanced under a large external magnetic field (Bext), which is caused by the antiferromagnetic exchange coupling fields weakening the influence of Bext. By fitting the Hall resistance curves, the field-like torque is demonstrated to be the main contribution to the Hall resistance. Interestingly, both the SOT effective fields are greatly enhanced for antiparallel alignment. This study separates the contributions of SOT and the thermoelectric effect in the SyAF structures and enables the design of the spintronic devices with stability under a large magnetic field. [ABSTRACT FROM AUTHOR]

Magnetothermal applications of nanoparticles in biomedicine are currently limited by low thermal responses to oscillating magnetic fields on one side and by detrimental physiological effects of electromagnetic radiation on the other side. In this paper, using Zn–Mn ferrite nanoparticles, we demonstrate that an appropriate choice of size and chemical composition of magnetic nanoparticles results in the superquadratic (upto 5th power) dependence of the Specific Absorption Rate (SAR) on a magnetic field (SAR proportional to H5). This gives an opportunity to obtain SAR values above 10 W/g in an oscillating magnetic field, while maintaining the field-frequency product at a level close to the physiological Brezovich's limit ∼ 109A/(m s). [ABSTRACT FROM AUTHOR]

Scanning magnetometry with nitrogen-vacancy (NV) centers in diamond has emerged as a powerful microscopy for studying weak stray field patterns with nanometer resolution. Due to the internal crystal anisotropy of the spin defect, however, external bias fields—critical for the study of magnetic materials—must be applied along specific spatial directions. In particular, the most common diamond probes made from {100}-cut diamond only support fields at an angle of θ = 55 ° from the surface normal. In this paper, we report fabrication of scanning diamond probes from {110}-cut diamond where the spin anisotropy axis lies in the scan plane (θ = 90 °). We show that these probes retain their sensitivity in large in-plane fields and demonstrate scanning magnetometry of the domain pattern of Co–NiO films in applied fields up to 40 mT. Our work extends scanning NV magnetometry to the important class of materials that require large in-plane fields. [ABSTRACT FROM AUTHOR]

Electrically charged porous electret films, reported as ferroelectrets or piezoelectrets, have drawn the attention of researchers due to their high piezoelectric activity, low density, and flexibility. This paper introduces a ferroelectret design for the development of piezoelectric-magnetic responses. Samples are prepared with an additional magnetic layer placed above open tubular channels made from fused electret films, and the piezoelectric direct effect of electrically charged samples is monitored. The results of the measurements show approximately 900 pC N−1 piezoelectric coefficients d33. The piezoelectric-magnetic effect is an electrical response from a mechanical deformation caused by an external magnetic force. The magnetic field pulls the magnetic layer, mechanically deforming the electrically charged tubular structure, which creates a charge compensation to be measured as a charge density variation. A setup especially assembled for measuring the piezoelectric-magnetic response is described together with piezoelectric-magnetic values ranging from 94 up to 275 pC T−1. [ABSTRACT FROM AUTHOR]

The planar topological Hall effect (PTHE), appearing when the magnetic field tended to be along the current, is believed to result from the real-space Berry curvature of the spin spiral structure and has been experimentally observed in skyrmion-hosting materials. In this paper, we report an experimental observation of the PTHE in a hexagonal ferromagnetic Fe5Sn3 single crystal. With a current along the c axis of Fe5Sn3, the transverse resistivity curves exhibited obvious peaks near the saturation field as the magnetic field rotated to the current and appeared more obvious with increasing temperature, which was related to the noncoplanar spin structure in Fe5Sn3. This spin structure induced nonzero scalar spin chirality, which acted as fictitious magnetic fields to conduction electrons and contributed the additional transverse signal. These findings deepen the understanding of the interaction between conduction electrons and complex magnetic structures and are instructive for the design of next-generation spintronic devices. [ABSTRACT FROM AUTHOR]

This paper studies the behavior of rotating magnetic microrobots, constructed with a permanent magnet or a soft ferromagnet, when the applied magnetic field rotates faster than a microrobot's step-out frequency (the frequency requiring the entire available magnetic torque to maintain synchronous rotation). A microrobot's velocity dramatically declines when operated above the step-out frequency. As a result, it has generally been assumed that microrobots should be operated beneath their step-out frequency. In this paper, we report and demonstrate properties of a microrobot's behavior above the step-out frequency that will be useful for the design and control of multi-microrobot systems. [ABSTRACT FROM AUTHOR]

Magnetoelectric energy converters are specific energy converters that utilize the magnetoelectric effect to generate an electric polarization response to an applied magnetic field or, conversely, a magnetization response to an electric field. Prior studies reported magnetoelectric energy converters with an efficiency of more than 80%. However, these converters require DC magnet bias to achieve such a high efficiency and bulky electromagnetic magnets or Helmholtz coils were utilized to provide the DC magnet bias, which limits their applications in portable electronics, internet of things, or medical applications. In this paper, a standalone magnetoelectric energy converter that does not require a bulky DC magnet field is presented. It is based on a tri-layer of Terfenol-D (TbDyFe2) and lead zirconate titanate. A measured high energy conversion efficiency of 88% and a small volume of 1.356 cm3 are demonstrated when operating at its fundamental mechanical resonance frequency of 34.6 kHz. The factors that affect its efficiency are discussed including tri-layer thickness ratio, operation frequency, and load resistance. The energy converter based on the magnetoelectric effect with a high efficiency and small volume could have potential applications in portable electronics, internet of things systems, and wireless charging. [ABSTRACT FROM AUTHOR]

We demonstrate two-dimensional mapping of current flow in graphene devices by using a single-spin scanning magnetometer based on a nitrogen-vacancy defect center in diamond. We first image the stray magnetic field generated by the current and then reconstruct the current density map from the field data. We focus on the visualization of current flow around a small sized current source of ∼500 nm diameter, which works as an effective point contact. In this paper, we study two types of point-contacted graphene devices and find that the overall current profiles agree with the expected behavior of electron flow in the diffusive transport regime. This work could offer a route to explore interesting carrier dynamics of graphene including ballistic and hydrodynamic transport regimes. [ABSTRACT FROM AUTHOR]

This paper studies spin–orbit torque (SOT) switching behaviors in synthetic antiferromagnet (SyAF) structures of Ta/[Pt/Co]m/Ru/[Co/Pt]n, which are asymmetric between the upper multilayer (UML) and the bottom multilayer (BML). The SOT-induced magnetization switching loops show multiple transitions of switching orientations between clockwise and anticlockwise with an increasing in-plane magnetic field, determined by the effects of the Dzyaloshinskii–Moriya interaction from both the BML and UML in the different stacking structures. Moreover, the field-free SOT switching was observed in the structure of Ta/[Pt/Co]3/Ru (0.5)/[Co/Pt]4. It can be attributed to the horizontal component of magnetic moments in its UML acting as an equivalent field. Therefore, the SyAF structures could be potential candidates for the future SOT-based spintronic devices. [ABSTRACT FROM AUTHOR]

In this paper, the controlled support of a magnetic fluid at a superhydrophobic interface is proposed. It is shown experimentally that the support of the magnetic fluid has excellent dynamic response characteristics and can be enhanced by increasing the magnetic field intensity. Numerical simulations are performed to clarify how the magnetic field is distributed, and the support mechanism is revealed theoretically. This study provides further physical insight into liquid-based support and offers excellent prospects for frictionless and controllable micro-platforms and laboratory-on-chip applications. [ABSTRACT FROM AUTHOR]

In this paper, we report a cavity magnonic system consisting of a split-ring resonator coupled with a yttrium iron garnet sphere, in which both coherent and dissipative coupling strengths can be tuned continuously, thereby making the zero damping conditions (ZDCs) controllable in a frequency range up to 100 MHz. Unidirectional invisibility has been observed under the ZDCs, with the microwaves freely transmitted in the forward direction (−2.9 dB) but almost completely blocked in the backward direction (−83 dB). The effective isolation ratio reaches up to 80 dB, which has surpassed the ideal isolation ratio limited by the state-of-the-art technique, and its direction is reversible by the orientation of the external static magnetic field. As an unconventional nonreciprocal device with flexibility and sensitivity, our magnonic device may open a promising way for robust coherent and quantum information processing. [ABSTRACT FROM AUTHOR]

In a nuclear spin co-magnetometer, it was found that the probe light parameters have a significant impact on the transverse residual magnetic field compensation. In this paper, we demonstrated that this effect is caused by the tensor light shifts of the linearly polarized probe light. This effect can be suppressed at a certain probe light polarization. We obtained this probe light polarization experimentally and reduced the impact of probe power on magnetic field compensation by 35 times. The impact of probe light frequency is also suppressed. Furthermore, the influence of the pump power, the static magnetic field, and the cell temperature on this optimized polarization was investigated. The tensor light shift can be suppressed at about 17 ° polarization under different conditions in our system. Moreover, the actual residual magnetic field in the magnetic shields can be obtained, which is useful for the magnetic field design of the co-magnetometer, and this method can also be extended to other atomic devices to suppress the tensor light shift. [ABSTRACT FROM AUTHOR]

Magnetic flux modulation technology aims to shift the low frequency or dc magnetic field to a higher frequency band and avoid the influence of 1/f noise in a magnetoresistance sensor. Despite decades of development, there are relatively few studies devoted to the impact of this technology on the noise characteristic of a magnetoresistance sensor. In this paper, we fabricated a tunnel magnetoresistance sensor integrated with a magnetic flux modulation structure and explored the noise characteristics under modulation. It was found that the noise at the modulation frequency will increase significantly when the external magnetic field is large, and this is caused by the ac magnetic field after modulation. The maximum value of noise at the modulation frequency is up to 12 μV/√Hz under modulation, which is 63 times higher than that without modulation. Obviously, this result indicates that magnetic flux modulation technology may be ineffective in reducing 1/f noise. Fortunately, it was also observed that when the external magnetic field is small, the noise increase is not obvious. Based on this, we proposed a magnetic field tracking compensation method to keep the measured magnetic field constantly close to zero and prevent the deterioration of noise, no matter how the external magnetic field changes. A compensating coil was designed and manufactured to generate the compensating magnetic field. The test results show that the increase in noise under modulation can be well suppressed with magnetic field tracking compensation. [ABSTRACT FROM AUTHOR]

Magnetic field generation by laser-driven coils is a promising way of magnetizing plasma in laboratory high-energy-density plasma experiments. A typical configuration consists of two electrodes—one electrode is irradiated with a high-intensity laser beam and another electrode collects charged particles from the expanding plasma. The two electrodes are separated by a narrow gap forming a capacitor-like configuration and are connected with a conducting wire-coil. The charge-separation in the expanding plasma builds up a potential difference between the electrodes that drives the electrical current in the coil. A magnetic field of tens to hundreds of Teslas generated inside the coil has been reported. This paper presents a simple model that estimates the magnetic field using simple assumptions. The results are compared with the published experimental data. [ABSTRACT FROM AUTHOR]

In a previous paper [X. Wang et al., J. Appl. Phys. 120, 014903 (2016)], several experimental devices have been presented, which demonstrate the efficiency of electromagnetic techniques for detecting and sizing electrically insulating particles entrained in the flow of a molten metal. In each case, a nonuniform magnetic field is applied across the flow of the electrically conducting liquid, thereby generating a braking Lorentz force on this moving medium and a reaction force on the magnet, which tends to be entrained in the flow direction. The purpose of this letter is to derive scaling laws for this Lorentz force from an elementary theoretical model. For simplicity, as in the experiments, the flowing liquid is modeled as a solid body moving with a uniform velocity U. The eddy currents in the moving domain are derived from the classic induction equation and Ohm's law, and expressions for the Lorentz force density j × B and for its integral over the entire moving domain follow. The insulating particles that are eventually present and entrained with this body are then treated as small disturbances in a classic perturbation analysis, thereby leading to scaling laws for the pulses they generate in the Lorentz force. The purpose of this letter is both to illustrate the eddy currents without and with insulating particles in the electrically conducting liquid and to derive a key relation between the pulses in the Lorentz force and the main parameters (particle volume and dimensions of the region subjected to the magnetic field). [ABSTRACT FROM AUTHOR]

In this paper, we show that the widely accepted method of the determination of Curie temperature (TC) in (Ga,Mn)As samples, based on the position of the peak in the temperature derivative of the resistivity, completely fails in the case of non-metallic and low-TC unannealed samples. In this case, we propose an alternative method, also based on electric transport measurements, which exploits temperature dependence of the second derivative of the resistivity upon magnetic field. [ABSTRACT FROM AUTHOR]

This paper investigates the dynamic ac susceptibility (ACS) and the Brownian relaxation time of magnetic nanoparticles (MNPs) in dc magnetic fields with arbitrary orientations with respect to the ac magnetic field. A CoFe2O4 MNP sample, dominated by Brownian relaxation, is used to perform ACS measurements in an ac magnetic field with a constant amplitude of 0.2 mT (from 2 to 3000 Hz) and a superposed dc magnetic field with amplitudes ranging from 0 to 5 mT. Experimental results indicate that the ACS and Brownian relaxation time are significantly affected not only by the strength but also by the orientation of the dc magnetic field. Moreover, a mathematical model is proposed to analyze the ACS and Brownian relaxation time in dependence of the orientation of the dc magnetic field, which extends the established models parallel or perpendicular to arbitrary-oriented dc magnetic fields. Experimental results indicate that the good fitting between the experimental data (ACS and Brownian relaxation time) and the proposed models demonstrates the feasibility of the proposed model for the description of ACS and Brownian relaxation time in arbitrary-orientated ac and dc magnetic fields. [ABSTRACT FROM AUTHOR]

In this paper, we present the proof-of-concept of a device for rectifying ac-magnetic-field effects by mixing thermal spin and charge currents. The device consists of a NiO/Pt bilayer in which a pure spin current is generated perpendicularly to the sample plane by means of the spin Seebeck effect. The pure spin current, created in the NiO layer, is injected into the Pt layer and is converted into a charge current by means of the inverse spin Hall effect, which is measured by electrical contacts. Due to the combination of two effects, the spin Seebeck and the planar Nernst effect, the overall response of the device as a function of a magnetic field is similar to the one of a rectifying diode. The resulting charge current mainly flows in one direction, approaching zero for negative values of the magnetic field when the spin Seebeck voltage has an opposite sign and magnitude close to the planar Nernst effect contribution. This remarkable effect is well explained by analyzing the response function as well as taking into account the magnon diffusion theory for the spin Seebeck effect. We believe that this proof of concept is of interest to the development of spintronic devices. [ABSTRACT FROM AUTHOR]

Magnetic force microscopy (MFM) allows detection of stray magnetic fields around magnetic materials and the two-dimensional visualization of these fields. This paper presents a theoretical analysis of the oscillations of an MFM tip above a thin film of nonmagnetic metal. The results show good agreement with experimental data obtained by varying the tip height. The phenomenon analyzed here can be applied as a "metal detector" at the nanometer scale and for contactless measurements of sheet resistivity. The detection sensitivity is obtained as a function of oscillation frequency, thus allowing the determination of the best frequency for the phase-shift measurement. The shift in resonance frequency due to the presence of a nonmagnetic metal is also discussed. [ABSTRACT FROM AUTHOR]

Bistable structures featuring two stable states have been widely applied in designing fast and high-force-output actuators under various types of stimuli, such as mechanical force, swelling, thermal expansion, and so on. In this paper, we designed a magneto-actuated mechanism to realize the reversible shape transition between two curved stable configurations of a buckled beam using magneto actuation. The beam is composed of a silicone elastomer matrix with embedded micro-sized iron particles. The magnetic response of these iron particles endows the composite beam with the ability to snap from one stable shape to the other when the magnitude of the surrounding magnetic field exceeds the threshold value. By separately analyzing the electric-magnetic field and the magnetic-mechanical field, we formulate a simple and efficient computational method to numerically predict the critical current on the onset of snap-through. The computational and experimental critical currents show good agreement for different material and geometrical parameters, including the thickness of the beams, iron particle mixing ratios of the material, and the distances of the beam to the electromagnet. The proof-of-concept design is demonstrated to be efficient in the application of a magneto-responsive soft switch and a catapult for ejecting small objects, providing new insights into designing contactless, low-voltage-actuated bistable structures. [ABSTRACT FROM AUTHOR]

Untethered robotic microswimmers are very promising to significantly improve various types of minimally invasive surgeries by offering high accuracy at extremely small scales. A prime example is drug delivery, for which a large number of microswimmers is required to deliver sufficient dosages to target sites. For this reason, the controllability of groups of microswimmers is essential. In this paper, we demonstrate simultaneous control of multiple geometrically similar but magnetically different microswimmers using a single global rotating magnetic field. By exploiting the differences in their magnetic properties, we triggered different swimming behaviors from the microswimmers by controlling the frequency and the strength of the global field, for example, one swim and the other does not while exposed to the same control input. Our results show that the balance between the applied magnetic torque and the hydrodynamic torque can be exploited for simultaneous control of two microswimmers to swim in opposite directions, with different velocities, and with similar velocities. This work will serve to establish important concepts for future developments of control systems to manipulate multiple magnetically actuated microswimmers and a step towards using swarms of microswimmers as viable workforces for complex operations. [ABSTRACT FROM AUTHOR]

In this paper, perpendicular magnetic anisotropy (PMA) is tailored by changing the thickness of the free layer with the objective of producing MTJ nanopillars with a smooth linear resistance dependence with both the in-plane magnetic field and DC bias. We furthermore demonstrate how this linear bias dependence can be used to create a zero-threshold broadband voltage rectifier, a feature which is important for rectification in wireless charging and energy harvesting applications. By carefully balancing the amount of PMA acting in the free layer, the measured RF to DC voltage conversion efficiency can be made as large as 11%. [ABSTRACT FROM AUTHOR]

The importance of cell manipulation and cultivation is increasing rapidly in various fields, such as drug discovery, regenerative medicine, and investigation of new energy sources. This paper presents a method to transport cells in a microfluidic chip without contact. A local vortex was generated when high-frequency oscillation of a microtool was induced in a microfluidic chip. The vortex was controlled by tuning the tool’s oscillation parameters, such as the oscillation amplitude and frequency. The cells were then transported in the chip based on the direction of the tool’s movement, and their position, posture, and trajectories were controlled. Bovine oocyte manipulations, that is, transportation and rotation, were conducted to demonstrate the capability of the proposed method, without any contact by the microrobot with high-frequency oscillation. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate that in Ta/MgO/IrMn tunneling junctions, containing no ferromagnetic elements, distinct metastable resistance states can be set by field cooling the devices from above the Néel temperature (TN) along different orientations. Variations of the resistance up to 10% are found upon field cooling in applied fields, in-plane or out-of-plane. Well below TN, these metastable states are insensitive to magnetic fields up to 2 T, thus constituting robust memory states. Our work provides the demonstration of an electrically readable magnetic memory device, which contains no ferromagnetic elements and stores the information in an antiferromagnetic active layer. [ABSTRACT FROM AUTHOR]

This paper reports a bioassay of alpha-fetoprotein (AFP) concentration achieved via the measurement of blocking temperature (TB). Biofunctionalized magnetic nanoparticles (BMNs) consisting of anti-alpha-fetoprotein coated onto dextran-coated magnetic nanoparticles composed of Fe3O4 were prepared and then conjugated with AFP biotargets. It was found that both the saturation magnetization and value of TB increased with the concentration of the associated AFP. Furthermore, the dependence of TB of the samples on magnetic field agreed with the interparticle interaction model. Thus, this study demonstrated a platform to detect biomarkers by characterizing TB with a sensitivity limit of 20 ppb of AFP. The promising results obtained for this bioassay can be attributed to the interparticle interactions and Neel motions of magnetic moments in the BMNs. [ABSTRACT FROM AUTHOR]

Proposals for studying topological superconductivity and Majorana bound states in a nanowire proximity coupled to superconductors require that transport in the nanowire is ballistic. Previous works on hybrid nanowire-superconductor systems have shown evidence for Majorana bound states, but these experiments were also marked by disorder, which disrupts ballistic transport. In this paper, we demonstrate ballistic transport in the InSb nanowires interfaced directly with superconducting Al by observing quantized conductance at zero-magnetic field. Additionally, we demonstrate that the nanowire is proximity coupled to the superconducting contacts by observing Andreev reflection. These results are important steps for robustly establishing topological superconductivity in the InSb nanowires. [ABSTRACT FROM AUTHOR]

In this paper, we report the heating properties of gold-magnetite (Au-Fe3O4) heterodimer nanoparticles (NPs) subjected to an alternating magnetic field. The Au-Fe3O4 NPs coated with oleic acid and oleylamine (OA) were synthesized through a method that combines seed mediation and hightemperature decomposition. The coating was replaced with dimercaptosuccinic acid (DMSA) by the ligand-exchange method. The specific absorption rates (SARs) for the OA- and DMSA-coated Au-Fe3O4 NPs coated with OA and DMSA at room temperature were determined through the calorimetric and magnetometric methods. SAR depended on the square of the magnetic field H up to an H value of 4 kA/m. The absolute value of the SAR for DMSA-coated NPs is about fivefold higher than that of the OA-coated NPs. The AC magnetic hysteresis measurements showed the recovery of the magnetic volume and the decrease in the magnetic anisotropy of the DMSA-coated NPs relative to those of the OA-coated NPs. These results suggest that the protective agent influences the magnetic properties of magnetite NPs via gold NPs. [ABSTRACT FROM AUTHOR]

We have detected two typing errors in Fig. 2 of the published paper.1 The direct magnetoelectric (ME) measurements were carried out by sweeping magnetic fields of "100 Oe/s" for Fig. 2(a) and "5 Oe/s" for Figs. 2(b) and 2(c). The direct ME coefficient (αH) and the electric polarization (P) published in the paper were calculated from these correct sweep rates. Therefore, these errors do not alter the results and the discussions of our paper. [ABSTRACT FROM AUTHOR]

This document is an erratum for a letter published in the journal Applied Physics Letters. The erratum corrects an error in Equation (4) of the original letter, which was missing a factor of two. The correct equation is provided, along with an explanation of the error and the correct average energy in an RLC resonator. The authors acknowledge the error and thank Dr. Gergö Fülöp for bringing it to their attention, but state that the error does not affect the analysis or conclusions of the original paper. [Extracted from the article]

In this paper we demonstrate spintronic devices which combine magnetic tunnel junctions with a spin-filtering tunnel barrier. These consist of an ultrathin ferromagnetic insulating barrier, Sm0.75Sr0.25MnO3, sandwiched between two ferromagnetic half-metallic manganite electrodes, La0.7Sr0.3MnO3 and La0.7Ca0.3MnO3, in a nanopillar structure. Depending on the relative magnetic configurations of barrier and electrode layers, three resistance states are well defined, which therefore represent a potential three-state memory concept. These results open the way for the development of spintronic devices by exploiting the many degrees of freedom of perovskite manganite heterostructure systems. [ABSTRACT FROM AUTHOR]

This paper presents a triple-wavelength infrared plasmonic thermal emitter using a periodic arrangement of hybrid dielectric materials within a tri-layer metal/dielectric/metal structure. The proposed arrangement makes it possible to sustain multiple resonance of localized surface plasmons (LSP), thereby providing an additional degree of freedom by which to vary the resonant wavelengths in the medium infrared region. Variations in the effective refractive index due to the different modal distribution within dielectric gratings results in multiple LSP resonances, and the resonant wavelengths can be easily tuned by altering the compositions of hybrid dielectric materials. The measured dispersion relation diagram and the finite difference time domain simulation indicated that the resonances were localized. They also indicate that the magnetic fields generated by the multiple LSP modes exhibit distribution patterns similar to that of a standing wave in the periodic arrangement of the hybrid dielectric layer, each of which presents an emission peak corresponding to a different modal order. [ABSTRACT FROM AUTHOR]

Previous work has demonstrated that the radio frequency surface resistance of niobium resonators is dramatically reduced when nitrogen impurities are dissolved as interstitial in the material. This effect is attributed to the lowering of the Mattis-Bardeen surface resistance with increasing accelerating field; however, the microscopic origin of this phenomenon is poorly understood. Meanwhile, an enhancement of the sensitivity to trapped magnetic field is typically observed for such cavities. In this paper, we conduct a systematic study on these different components contributing to the total surface resistance as a function of different levels of dissolved nitrogen, in comparison with standard surface treatments for niobium resonators. Adding these results together, we are able to show which is the optimum surface treatment that maximizes the Q-factor of superconducting niobium resonators as a function of expected trapped magnetic field in the cavity walls. These results also provide insights on the physics behind the change in the field dependence of the Mattis-Bardeen surface resistance, and of the trapped magnetic vortex induced losses in superconducting niobium resonators. [ABSTRACT FROM AUTHOR]

In this paper, a method for formation of nanoparticle composed wires of magnetic materials is presented. The method is based on ultrashort laser ablation in air at atmospheric pressure in the presence of external magnetic field. The material ablated at these conditions is composed of nanosized spherical particles that form chains with length of a few tens of microns. These structures are deposited on the substrate's surface as they are arranged parallel to the applied magnetic field. The obtained results can be used for designing a technology for magnetic materials assembly at open environment conditions. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of a controlled cooling rate on magnetic field reversal assisted by spin transfer torque (STT) in thermally assisted magnetic random access memory. By using a gradual linear decrease of the voltage at the end of the write pulse, the STT decays more slowly or at least at the same rate as the temperature. This condition is necessary to make sure that the storage layer magnetization remains in the desired written direction during cooling of the cell. The influence of the write current pulse decay rate was investigated on two exchange biased synthetic ferrimagnet (SyF) electrodes. For a NiFe based electrode, a significant improvement in writing reproducibility was observed using a gradual linear voltage transition. The write error rate decreases by a factor of 10 when increasing the write pulse fall-time from ~3 ns to 70 ns. For comparison, a second CoFe/NiFe based electrode was also reversed by magnetic field assisted by STT. In this case, no difference between sharp and linear write pulse fall shape was observed. We attribute this observation to the higher thermal stability of the CoFe/NiFe electrode during cooling. In real-time measurements of the magnetization reversal, it was found that Ruderman-Kittel-Kasuya- Yosida (RKKY) coupling in the SyF electrode vanishes for the highest pulse voltages that were used due to the high temperature reached during write. As a result, during the cooling phase, the final state is reached through a spin-flop transition of the SyF storage layer. [ABSTRACT FROM AUTHOR]

This paper presents a 3-axis Lorentz force magnetometer based on an encapsulated micromechanical silicon resonator having three orthogonal vibration modes, each measuring one vector component of the external magnetic field. One mode, with natural frequency fn) of 46.973 kHz and quality factor (Q) of 14918, is operated as a closed-loop electrostatically excited oscillator to provide a frequency reference for 3-axis sensing and Lorentz force generation. Current, modulated at the reference frequency, is injected into the resonator, producing Lorentz force that is centered at the reference frequency. Lorentz force in the first axis is nulled by the oscillator loop, resulting in force-rebalanced operation. The bandwidth and scale-factor of this force-rebalanced axis are independent of resonator Q, improving the sensor's temperature coefficient from 20 841ppm/°C to 424ppm/°C. The frequencies of the other two modes are closely spaced to the first mode's reference frequency and are demonstrated to track this frequency over temperature within 1 ppm/K. Field measurements in these two axes are conducted open-loop and off-resonance, ensuring that the scale-factor is independent of Q to first order and producing a measurement bandwidth of over 40 Hz. [ABSTRACT FROM AUTHOR]