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Modulation of the energy landscape by external perturbations governs various thermally-activated phenomena, described by the Arrhenius law. Thermal fluctuation of nanoscale magnetic tunnel junctions with spin-transfer torque (STT) shows promise for unconventional computing, whereas its rigorous representation, based on the Néel-Arrhenius law, has been controversial. In particular, the exponents for thermally-activated switching rate therein, have been inaccessible with conventional thermally-stable nanomagnets with decade-long retention time. Here we approach the Néel-Arrhenius law with STT utilising superparamagnetic tunnel junctions that have high sensitivity to external perturbations and determine the exponents through several independent measurements including homodyne-detected ferromagnetic resonance, nanosecond STT switching, and random telegraph noise. Furthermore, we show that the results are comprehensively described by a concept of local bifurcation observed in various physical systems. The findings demonstrate the capability of superparamagnetic tunnel junction as a useful tester for statistical physics as well as sophisticated engineering of probabilistic computing hardware with a rigorous mathematical foundation.

Electrical manipulation of magnetic materials by current-induced spin torque constitutes the basis of spintronics. Here, we show an unconventional response to spin–orbit torque of a non-collinear antiferromagnet Mn3Sn, which has attracted attention owing to its large anomalous Hall effect despite a vanishingly small net magnetization. In epitaxial heavy-metal/Mn3Sn heterostructures, we observe a characteristic fluctuation of the Hall resistance under the application of electric current. This observation is explained by a rotation of the chiral-spin structure of Mn3Sn driven by spin–orbit torque. We find that the variation of the magnitude of anomalous Hall effect fluctuation with sample size correlates with the number of magnetic domains in the Mn3Sn layer. In addition, the dependence of the critical current on Mn3Sn layer thickness reveals that spin–orbit torque generated by small current densities, below 20 MA cm−2, effectively acts on the chiral-spin structure even in Mn3Sn layers that are thicker than 20 nm. The results provide additional pathways for electrical manipulation of magnetic materials. Current-induced rotation in epitaxial films of the non-collinear antiferromagnet Mn3Sn is investigated.

The mutual synchronization of spin-torque oscillators (STOs) is critical for communication, energy harvesting and neuromorphic applications. Short range magnetic coupling-based synchronization has spatial restrictions (few µm), whereas the long-range electrical synchronization using vortex STOs has limited frequency responses in hundreds MHz (, Spin torque oscillators (STOs) are attractive potential alternative for many high frequency applications, due to their small area and CMOS compatibility. Here, Sharma et al succeed in the electrical synchronization of four STOs, and use their setup to demonstrate wireless and battery-free energy harvesting using eight STOs.

Spin-orbit torque, a torque brought about by in-plane current via the spin-orbit interactions in heavy-metal/ferromagnet nanostructures, provides a new pathway to switch the magnetization direction. Although there are many recent studies, they all build on one of two structures that have the easy axis of a nanomagnet lying orthogonal to the current, that is, along the z or y axes. Here, we present a new structure with the third geometry, that is, with the easy axis collinear with the current (along the x axis). We fabricate a three-terminal device with a Ta/CoFeB/MgO-based stack and demonstrate the switching operation driven by the spin-orbit torque due to Ta with a negative spin Hall angle. Comparisons with different geometries highlight the previously unknown mechanisms of spin-orbit torque switching. Our work offers a new avenue for exploring the physics of spin-orbit torque switching and its application to spintronics devices.

The creep motion of domain walls in magnetic metals can belong to different universality classes depending on whether they are driven by magnetic fields or spin-polarized currents.

This Review discusses recent advances towards electric-field control of magnetism in ferromagnetic semiconductors and metals, and in multiferroics. The electrical manipulation of magnetism and magnetic properties has been achieved across a number of different material systems. For example, applying an electric field to a ferromagnetic material through an insulator alters its charge-carrier population. In the case of thin films of ferromagnetic semiconductors, this change in carrier density in turn affects the magnetic exchange interaction and magnetic anisotropy; in ferromagnetic metals, it instead changes the Fermi level position at the interface that governs the magnetic anisotropy of the metal. In multiferroics, an applied electric field couples with the magnetization through electrical polarization. This Review summarizes the experimental progress made in the electrical manipulation of magnetization in such materials, discusses our current understanding of the mechanisms, and finally presents the future prospects of the field.

In the version of this Review Article originally published, the affiliations of the authors J. Železný, P. Wadley and K. Olejnik were incorrect and should have read: “J. Železný1,2, P. Wadley3, K. Olejnik2. 1Max Planck Institute for Chemical Physics of Solids, Dresden, Germany. 2Institute of Physics, Academy of Sciences of the Czech Republic, Praha, Czech Republic. 3School of Physics and Astronomy, University of Nottingham, Nottingham, UK.” These have now been corrected in the online versions.

The quantum Hall effect arises from the cyclotron motion of charge carriers in two-dimensional systems. However, the ground states related to the integer and fractional quantum Hall effect, respectively, are of entirely different origin. The former can be explained within a single-particle picture; the latter arises from electron correlation effects governed by Coulomb interaction. The prerequisite for the observation of these effects is extremely smooth interfaces of the thin film layers to which the charge carriers are confined. So far, experimental observations of such quantum transport phenomena have been limited to a few material systems based on silicon, III-V compounds and graphene. In ionic materials, the correlation between electrons is expected to be more pronounced than in the conventional heterostructures, owing to a large effective mass of charge carriers. Here we report the observation of the fractional quantum Hall effect in MgZnO/ZnO heterostructures grown by molecular-beam epitaxy, in which the electron mobility exceeds 180,000 cm(2) V(-1) s(-1). Fractional states such as ν = 4/3, 5/3 and 8/3 clearly emerge, and the appearance of the ν = 2/5 state is indicated. The present study represents a technological advance in oxide electronics that provides opportunities to explore strongly correlated phenomena in quantum transport of dilute carriers.

Emphysematous cholecystitis (EC) is a life-threatening complication of acute cholecystitis. Its clinical manifestations are usually vague, but asymptomatic cases are very rare. We present such a case with an emphasis on sonographic (US) findings. In this case, detection of gas echoes in the gallbladder wall and the surrounding hepatic tissue led us to an appropriate treatment. US is now the technique of first choice for diagnosing gallbladder diseases, and knowledge of US findings encountered in this case can help prevent a hazardous delay in emergent treatment.

Conventional semiconductor devices use electric fields to control conductivity, a scalar quantity, for information processing. In magnetic materials, the direction of magnetization, a vector quantity, is of fundamental importance. In magnetic data storage, magnetization is manipulated with a current-generated magnetic field (Oersted-Ampère field), and spin current is being studied for use in non-volatile magnetic memories. To make control of magnetization fully compatible with semiconductor devices, it is highly desirable to control magnetization using electric fields. Conventionally, this is achieved by means of magnetostriction produced by mechanically generated strain through the use of piezoelectricity. Multiferroics have been widely studied in an alternative approach where ferroelectricity is combined with ferromagnetism. Magnetic-field control of electric polarization has been reported in these multiferroics using the magnetoelectric effect, but the inverse effect-direct electrical control of magnetization-has not so far been observed. Here we show that the manipulation of magnetization can be achieved solely by electric fields in a ferromagnetic semiconductor, (Ga,Mn)As. The magnetic anisotropy, which determines the magnetization direction, depends on the charge carrier (hole) concentration in (Ga,Mn)As. By applying an electric field using a metal-insulator-semiconductor structure, the hole concentration and, thereby, the magnetic anisotropy can be controlled, allowing manipulation of the magnetization direction.

Splenic inflammatory pseudotumor is a rare pathology, and the literature stresses the difficulty of preoperative diagnosis. There are no previous reports of contrast-enhanced ultrasound findings for this tumor in the literature. Our case appears to be the first to be examined using this technique. In our case, contrast-enhanced ultrasound showed the mass to be homogeneously and less enhanced than the surrounding parenchyma in all phases, and it included fine enhanced spots. We also briefly review the literature.

We present two cases of subcutaneous hematoma in which color Doppler US revealed colored areas under probe compression, and Doppler waveforms obtained from these areas changed rapidly (from a constant flow to a pulsatile flow, and from a high-velocity flow to a slow-velocity flow) according to the degree of probe compression. In our cases, a sufficient number of blood cells within the lesion moving under probe compression was thought to give rise to Doppler signals and changes in Doppler waveforms.

Ternary phase composition-spread thin film libraries, TiO2-ZrO2-HfO2, were synthesized by using a combinatorial pulsed laser deposition system. The composition, crystalline structure, and optical transmission properties were characterized in a high-throughput way. TiO2 doped with Zr and Hf was found to exhibit a wider bandgap than pure TiO2; hence, these compounds can be used as wide gap semiconductors for heteroepitaxial spintronics devices, based on a ferromagnetic semiconductor, Co-doped TiO2.

Molecular beam epitaxy of GaSb films, with several percents of Cr, and their characterization are reported. Their electric and magnetic properties depend on their growth temperature and Cr composition. Although magnetization measurements reveal that all the films are ferromagnetic even at room temperature, this is most probably due to the precipitation of ferromagnetic zincblende CrSb. The magnetotransport measurements show that Cr spins may couple antiferromagnetically in GaSb host matrix.

Magnetic information storage relies on external magnetic fields to encode logical bits through magnetization reversal. But because the magnetic fields needed to operate ultradense storage devices are too high to generate, magnetization reversal by electrical currents is attracting much interest as a promising alternative encoding method. Indeed, spin-polarized currents can reverse the magnetization direction of nanometre-sized metallic structures through torque; however, the high current densities of 10(7)-10(8) A cm(-2) that are at present required exceed the threshold values tolerated by the metal interconnects of integrated circuits. Encoding magnetic information in metallic systems has also been achieved by manipulating the domain walls at the boundary between regions with different magnetization directions, but the approach again requires high current densities of about 10(7) A cm(-2). Here we demonstrate that, in a ferromagnetic semiconductor structure, magnetization reversal through domain-wall switching can be induced in the absence of a magnetic field using current pulses with densities below 10(5) A cm(-2). The slow switching speed and low ferromagnetic transition temperature of our current system are impractical. But provided these problems can be addressed, magnetic reversal through electric pulses with reduced current densities could provide a route to magnetic information storage applications.

Recent years have witnessed extensive research aimed at developing functional, tetrahedrally coordinated ferromagnetic semiconductors that could combine the resources of semiconductor quantum structures and ferromagnetic materials systems and thus lay the foundation for semiconductor spintronics. Spin-injection capabilities and tunability of magnetization by light and electric field in Mn-based III–V and II–VI diluted magnetic semiconductors are examples of noteworthy accomplishments. This article reviews the present understanding of carrier-controlled ferromagnetism in these compounds with a focus on mechanisms determining Curie temperatures and accounting for magnetic anisotropy and spin stiffness as a function of carrier density, strain, and confinement. Materials issues encountered in the search for semiconductors with a Curie point above room temperature are addressed, emphasizing the question of solubility limits and self-compensation that can lead to precipitates and point defects. Prospects associated with compounds containing magnetic ions other than Mn are presented.

We demonstrate electrical electron spin injection in a p+-(Ga,Mn)As/n+-GaAs tunnel junction with an n-GaAs/(In,Ga)As/p-GaAs light emitting diode (LED). By applying a reverse bias to the p+-(Ga,Mn)As/n+-GaAs junction (forward bias to the LED), we observed clear hysteresis in electroluminescence (EL) polarization. The magnitude of the EL polarization, which does not depend critically on the spacer layer thickness up to 800 nm, is found to be about five times greater than that of the hole spin injection.

We have investigated the magnetotransport properties of field-effect transistors (FET) having a III-V ferromagnetic semiconductor channel layer. One can control not only the ferromagnetic transition temperature T C but also the magnetization and the coercive force of (In,Mn)As channel layers isothermally and reversibly by gate electric fields. A small change of the magnetization upon application of gate electric fields is also observed in FETs with a (Ga,Mn)As channel. Results on a (Al,Ga,Mn)As channel FET are also presented.

Gate-voltage dependences of nuclear spin relaxation and decoherence times in a Schottky-gated n-GaAs/AlGaAs (110) quantum well (QW) are investigated by time-resolved Kerr-rotation measurements combined with pulsed-rf nuclear magnetic resonance (NMR). We show that the nuclear spin relaxation and decoherence times decrease with decreasing electron density, indicating that the hyperfine interaction is enhanced as the electronic states becomes localized in an impurity-doped QW.

We investigated the doping concentration (ND) dependence of the extrinsic spin Hall effect (SHE) in n-doped GaAs with ND raging from 3×1016 cm−3 to 5×1017 cm−3. By using scanning Kerr microscopy (SKM) measurements, we observed the Kerr rotation signal due to the spin accumulation near the channel edges in all the samples with different ND. Moreover, the position and in-plane magnetic field dependence of the Kerr rotation signal are found to vary with ND. We analyzed the ND dependence of the spin Hall conductivity by taking account of the ND-dependent spin lifetime based on the typical drift-diffusion model.

We have fabricated a series of field-effect transistor structures with a thin (Ga,Mn)As channel with thickness t of 3.5, 4.0, 4.5, and 5.0 nm, and investigated the effect of electric-field E on their magnetic properties. The Curie temperature T C showed a clear dependence on the magnitude of E, and its controllable range became larger with decreasing t and reached 15 K for the device with t=3.5 nm, which corresponded to 32% of T C of the layer.

The rate of the transformation from the metastable tetragonal to the monoclinic phase of ZrO2 was measured in air from 850°C to 1000°C by neutron diffraction. This rate was found to be temperature dependent, and its measured values were considerably lower then those reported previously. The kinetics of this phase transformation is discussed in terms of a modified ‚crystallite growth-martensitic transformation model' that includes the distribution of crystallite sizes.

There is a marked paucity of reports on contrast-enhanced ultrasonography (US) for focal splenic disease in the literature, and there are no previously reported contrast-enhanced US findings for splenic granuloma. We report the case of a 77-year-old cirrhotic woman with isolated splenic granulomas. We detail the diagnostic difficulty encountered in this case and briefly review the literature.

Current-induced magnetic domain wall motion is attractive for manipulating magnetization direction in spintronics devices, which open a new era of electronics. Up to now, in spite of a crucial significance to applications, investigation on a current-induced domain wall depinning probability, especially in sub-nano to a-few-nanosecond range has been lacking. Here we report on the probability of the depinning in perpendicularly magnetized Co/Ni nanowires in this timescale. A high depinning probability was obtained even for 2-ns pulses with a current density of less than 10¹² A m⁻². A one-dimensional Landau-Lifshitz-Gilbert calculation taking into account thermal fluctuations reproduces well the experimental results. We also calculate the depinning probability as functions of various parameters and found that parameters other than the coercive field do not affect the transition width of the probability. These findings will allow one to design high-speed and reliable magnetic devices based on the domain wall motion.

Spin pumping is the phenomenon that magnetization precession in a ferromagnetic layer under ferromagnetic resonance produces a pure spin current in an adjacent non-magnetic layer. The pure spin current is converted to a charge current by the spin-orbit interaction, and produces a d.c. voltage in the non-magnetic layer, which is called the inverse spin Hall effect. The combination of spin pumping and inverse spin Hall effect has been utilized to determine the spin Hall angle of the non-magnetic layer in various ferromagnetic/non-magnetic systems. Magnetization dynamics of ferromagnetic resonance also produces d.c. voltage in the ferromagnetic layer through galvanomagnetic effects. Here we show a method to separate voltages of different origins using (Ga,Mn)As/p-GaAs as a model system, where sizable galvanomagnetic effects are present. Neglecting the galvanomagnetic effects can lead to an overestimate of the spin Hall angle by factor of 8, indicating that separating the d.c. voltages of different origins is critical.

Energy barriers in magnetization reversal dynamics have long been of interest because the barrier height determines the thermal stability of devices as well as the threshold force triggering their dynamics. Especially in memory and logic applications, there is a dilemma between the thermal stability of bit data and the operation power of devices, because larger energy barriers for higher thermal stability inevitably lead to larger magnetic fields (or currents) for operation. Here we show that this is not the case for current-induced magnetic domain-wall motion induced by adiabatic spin-transfer torque. By quantifying domain-wall depinning energy barriers by magnetic field and current, we find that there exist two different pinning barriers, extrinsic and intrinsic energy barriers, which govern the thermal stability and threshold current, respectively. This unique two-barrier system allows low-power operation with high thermal stability, which is impossible in conventional single-barrier systems.

We studied the transport properties of spin-polarized conduction electrons in GaAs by time-resolved photoinjection and photoluminescence polarization measurements. Under an electric field of a few kV/cm, the degree of the spin polarization considerably decreases during drift transport over the distance shorter than 4 μm. Spin relaxation by D'yakonov–Perel' mechanism is suggested to be the cause of such a rapid spin depolarization for hot electrons under a moderate electric field at low temperatures.

Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton–exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72±0.05., As quantum information and communication experiments grow in sophistication, the need for efficient sources of entangled photons escalates. Using exciton and biexciton emission in GaAs island quantum dots, Ghali et al. demonstrate the electric field-induced generation of entangled photons with high fidelity.

It is often assumed that it is not possible to alter the properties of magnetic materials once they have been prepared and put into use. For example, although magnetic materials are used in information technology to store trillions of bits (in the form of magnetization directions established by applying external magnetic fields), the properties of the magnetic medium itself remain unchanged on magnetization reversal. The ability to externally control the properties of magnetic materials would be highly desirable from fundamental and technological viewpoints, particularly in view of recent developments in magnetoelectronics and spintronics. In semiconductors, the conductivity can be varied by applying an electric field, but the electrical manipulation of magnetism has proved elusive. Here we demonstrate electric-field control of ferromagnetism in a thin-film semiconducting alloy, using an insulating-gate field-effect transistor structure. By applying electric fields, we are able to vary isothermally and reversibly the transition temperature of hole-induced ferromagnetism.

Conventional electronics is based on the manipulation of electronic charge. An intriguing alternative is the field of ‘spintronics’, wherein the classical manipulation of electronic spin in semiconductor devices gives rise to the possibility of reading and writing non-volatile information through magnetism1,2. Moreover, the ability to preserve coherent spin states in conventional semiconductors3 and quantum dots4 may eventually enable quantum computing in the solid state5,6. Recent studies have shown that optically excited electron spins can retain their coherence over distances exceeding 100 micrometres (ref. 7). But to inject spin-polarized carriers electrically remains a formidable challenge8,9. Here we report the fabrication of all-semiconductor, light-emitting spintronic devices using III–V heterostructures based on gallium arsenide. Electrical spin injection into a non-magnetic semiconductor is achieved (in zero magnetic field) using a p-type ferromagnetic semiconductor10 as the spin polarizer. Spin polarization of the injected holes is determined directly from the polarization of the emitted electroluminescence following the recombination of the holes with the injected (unpolarized) electrons.

In situ X-ray diffraction study on KAlSi3O8 has been performed using the cubic type high pressure apparatus, MAX90, combined with synchrotron radiation. We determined the phase relations of sanidine, the wadeite-type K2Si4O9+kyanite (Al2SiO5)+coesite (SiO2) assemblage, and hollandite-type KAlSi3O8, including melting temperatures of potassic phases, up to 11 GPa. Our data on subsolidus phase boundaries are close to the recent data of Yagi and Akaogi (1991). Melting relations of sanidine are consistent with the low pressure data of Lindsley (1966). The breakdown of sanidine into three phases reduces melting temperature, and wadeite-type K2Si4O9 melts first around 1500° C in three phase coexisting region. Melting point of hollandite-type KAlSi3O8 is between 1700° C and 1800° C at 11 GPa. If these potassic phases host potassium in the earth's mantle, the true mantle solidus temperature will be much lower than the reported dry solidus temperature of peridotite.

A novel non-destructive way of characterizing electrical uniformity of semi-insulating GaAs substrates is presented, and applied to Cr-doped HB and undoped LEC wafers. The method utilizes photoconductance at microwave frequencies. Photoconduction is shown to be n-type in both type of substrates, and its magnitude is related to effective lifetime of photo-generated electrons on the basis of a simple theory developed here. Photoconductance variation in Cr-doped substrates is less pronounced, and is related to Cr acceptor concentration. On the other hand, photoconductance variation is more pronounced in undoped LEC substrates with U,M or W-shaped distribution. The photoconductance variation in LEC substrates reflects concentration fluctuation of residual acceptor such as carbon. The photoconductance technique collects information concerning the acceptor distribution near the surface which has a direct effect on the threshold voltage of FETs.

Silicon nitride films have been deposited by low frequency 50Hz plasma CVD using a nitrogen and silane mixture at room temperature. To deposit high quality silicon nitride, the silane fraction in the nitrogen and silane mixture has to be less than 5 %. The refractive index, breakdown field strength and resistivity of the obtained silicon nitride film were 2.0, 1.2x107 V/cm and 6x1015 Ωcm, respectively. Mechanism of the deposition of high quality silicon nitride is discussed on the basis of the experimentally observed light emission spectrum from the plasma and of the electron energy distribution function in the plasma theoretically calculated by the Boltzmann equation method.

Ga47In53As films have been grown by molecular beam epitaxy (MBE) on InP substrates. The unintentionally doped material has a free electron concentration of 8 × 1015cm-3 and exhibits sharp (~5 meV linewidth) exciton recombination in the 4K photoluminescence. The films were grown on (100) InP surfaces which were thermally cleaned in the arsenic beam. The effects of the substrate temperature during growth, the Ga to In flux ratio and the group V to group III flux ratio on the 4K photoluminescence are reported.