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The spin–orbit interaction (SOI), mainly manifesting itself in heavy elements and compound materials, has been attracting much attention as a means of manipulating and/or converting a spin degree of freedom. Here, we show that a Si metal-oxide- semiconductor (MOS) heterostructure possesses Rashba-type SOI, although Si is a light element and has lattice inversion symmetry resulting in inherently negligible SOI in bulk form. When a strong gate electric field is applied to the Si MOS, we observe spin lifetime anisotropy of propagating spins in the Si through the formation of an emergent effective magnetic field due to the SOI. Furthermore, the Rashba parameter α in the system increases linearly up to 9.8 × 10−16 eV m for a gate electric field of 0.5 V nm−1; that is, it is gate tuneable and the spin splitting of 0.6 μeV is relatively large. Our finding establishes a family of spin–orbit systems. Silicon is a light element with high lattice inversion symmetry, and so is not expected to possess a substantial spin–orbit interaction (SOI), which is desirable for spintronics. Here, a silicon-based heterostructure is demonstrated to have a gate-tuneable Rashba-type SOI.

Argan press cake (APC) is a by-product of argan oil extraction and is rich in cellulose, proteins, sucrose, phenolic compounds, and excessively bitter and acrid triterpenoids. Improvement in the antioxidant property of APC by fermentation (F-APC) with Lactiplantibacillus plantarum Argan-L2 has been reported. However, the bitter and acrid tastes remain in F-APC. Here, in order to determine the applicability of APC and F-APC as functional food materials by reducing its bitter taste, the effects of ethanol-precipitated APC and F-APC on mice fed a high-sucrose and low-fibre diet were determined. Compounds precipitated from 10% (w/v) APC and F-APC water suspensions with two volumes of ethanol were collected (APC-P, F-APC-P). The Institute of Cancer Research (ICR) mice were fed 50% (w/w) sucrose with no fibre (NF), 5% APC-P, or 5% F-APC-P for 14 days. The caecal microbiome was analysed via 16S rDNA (V4 region) sequencing. No bitter and acrid tastes were detected in the precipitates. Compared with those in the NF group, defaecation and the faecal weight were increased in the APC-P and F-APC-P groups. Additionally, blood lipid and glucose levels tended to be lower in the F-APC-P group. The abundance of caecal lactic acid-producing bacteria, such as Faecalibaculum rodentium and Lactobacillus johnsonii-like bacteria, was high in the APC-P group. In contrast, the abundance of indigenous L. plantarum-like bacteria was high in the F-APC-P group. APC-P and F-APC-P showed dietary fibre properties. Furthermore, APC-P and F-APC-P increased indigenous lactic acid bacteria OTUs, although the increased species were different in the two groups. These results suggest that both APC-P and F-APC-P have beneficial effects on the gut microbiome, environment, and host.

We demonstrated for the first time physically unclonable functions (PUFs) based on voltage-controlled magnetic tunnel junctions (VC-MTJs). The proposed PUF completely extracts the intrinsic variation of magnetization switching in the VC-MTJ as a random bit string without a short pulse, which is required in the spin-transfer torque (STT) MTJ and spin-orbit torque (SOT) MTJ-based PUF. Moreover, it can be initialized by a bias voltage without an external magnetic field. Using 40 MTJs fabricated in the same design, we evaluated the PUF fundamental parameters: uniqueness, reliability, and uniformity as 57.5%, 87.1%, and 45.0%, respectively.

Magnetic skyrmions are currently gaining attention owing to their potential to act as information carriers in spintronic devices. However, conventional techniques which rely on modulating the electric current to write or manipulate information using skyrmions are not energy efficient. Therefore, in this study, a Ta/Co–Fe–B/Ta/MgO junction that hosts a skyrmion was utilized to fabricate a device to investigate the effect of applying a voltage in the direction perpendicular to the film plane. Magneto-optical Kerr effect microscopy was performed in a polar configuration to observe the difference in the perpendicular magnetic anisotropy by observing the behavior of the magnetic domain structure and the skyrmions. Our findings suggest that voltage-induced magnetic domain structure modulation and the creation/annihilation of skyrmions are both possible. Furthermore, manipulation of skyrmions was realized by utilizing repulsive magnetic dipole interaction between the voltage-created skyrmion and skyrmion, exhibiting Brownian motion, outside the top electrode. Thus, our proposed method can enable controlling the creation and annihilation of skyrmions and their positions by manipulating the externally applied voltage. These findings can advance unconventional computing fields, such as stochastic and ultra-low-power computing.

To clarify the effect of rice bran (RB) and fermented RB (FRB) in a high-sucrose and low-dietary fibre diet on the gut microbiome, the in vitro bile acid-lowering capacity and caecal microbiota of ICR mice fed with 20% RB or FRB diets for two weeks were determined. The caecal microbiome was analysed by 16S rRNA gene amplicon sequencing. The in vitro bile acid-lowering capacity was high for FRB. In mouse experiments, triacylglycerol and total cholesterol were generally lower with FRB, although the faecal frequency was highest in mice fed with RB. The Shannon-Wiener and Simpson’s indices for alpha-diversity in the microbiome of mice fed with RB and FRB, were higher than mice fed the control diet. At the phylum level in the caecal microbiome, Firmicutes and Bacteroidetes were high with FRB and RB, respectively. At the operational taxonomic unit level, some bacterial groups related to diabetes and gut toxicity, such as Lachnospiraceae and Enterorhabdus mucosicola, were high for RB but not for FRB diets. These results suggest that FRB, rather than RB, intake improve the intestinal environment and blood lipid condition.

To clarify the presence of algal-susceptible indigenous bacteria (SIB) in the gut, ICR mice were fed high-sucrose (50% w/w) diets containing either no fibre (NF), 5% brown alga “arame”, Eisenia bicyclis; 5% red alga “tsunomata”, Chondrus ocellatus; 5% (w/w) green alga “hitoegusa”, Monostroma nitidum; or 5% (w/w) cyanobacterium “blue-green alga”, Aphanizomenon flos-aquae for 14 days. Faecal frequency and weight were the highest in mice fed M. nitidum. Plasma cholesterol was the lowest in the mice fed C. ocellatus. The caecal microbiome was examined by 16S rDNA (V4) amplicon sequencing. Principal component analysis of operational taxonomical units (OTUs) revealed that the edible algae altered the microbiome. An increase in abundance levels of OTUs by E. bicyclis (Bacteroides acidifaciens-, Bacteroides intestinalis-, Bifidobacterium pseudolongum-like), C. ocellatus (Bacteroides vulgatus- and Escherichia coli-like), M. nitidum (Faecalibaculum rodentium- and Muribaculum sp.-like), and A. flos-aquae (Muribaculum sp.) was detected. Abundance of Lactobacillus johnsonii was the lowest in mice fed the algal diets. Bacteria that increased in numbers were identified as algal SIBs. SIBs might have different effects on host health depending on the food material consumed. From the algal SIBs, B. pseudolongum, B. vulgatus, F. rodentium, and L. johnsonii were isolated using blood-liver agar and identified with the 16S rDNA BLAST search. Future studies should be focused on isolation of other SIBs.

A part of Lactobacillus plantarum and Lactococcus lactis subsp. lactis strains, isolated from coastal areas (Satoumi LAB) had shown acid, salt and bile resistances and good fermentation in soymilk rather than cow's milk. To prepare safer foods derived from fermented soymilk, Satoumi LAB strains were screened for antagonistic activity against Salmonella Typhimurium (ST) and Listeria monocytogenes (Lm) in brain heart infusion (BHI) broth. L. plantarum Tennozu-SU2 isolated from acorns showed 0.55 and 3.6 log CFU inhibitory effects against both ST and Lm, respectively. Six L. lactis strains suppressed 7 log CFU Lm. L. lactis BF1 isolated from salmon intestine also suppressed 0.95 log CFU ST. In a fermentation test, soymilk simultaneously inoculated with 6 or 7 log CFU/mL of ST or Lm, and 7 or 8 log CFU of Tennozu-SU2 or BF1 reduced Lm and ST counts by 2–6 log CFU/mL during 48 h fermentation. When soymilk fermented with Tennozu-SU2 or BF1 for 2 days and then inoculated with the pathogens, the counts of Lm and ST decreased during the 7 day storage at 10 °C, from 6 to 7 to 2–4 log CFU/mL. These results suggest that Tennozu-SU2 and BF1 are desirable as soymilk starters considering as they can improve food safety.

Improvement in the thermal tolerance of Si-based spin devices is realized by employing thermally stable nonmagnetic (NM) electrodes. For Au/Ta/Al electrodes, intermixing between Al atoms and Au atoms occurs at approximately 300 °C, resulting in the formation of a Au/Si interface. The Au–Si liquid phase is formed and diffuses mainly along an in-plane direction between the Si and AlN capping layers, eventually breaking the MgO layer of the ferromagnetic (FM) metal/MgO electrodes, which is located 7 µm away from the NM electrodes. By changing the layer structure of the NM electrode from Au/Ta/Al to Au/Ta, the thermal tolerance is clearly enhanced. Clear spin transport signals are obtained even after annealing at 400 °C. To investigate the effects of Mg insertion in FM electrodes on thermal tolerance, we also compare the thermal tolerance among Fe/Co/MgO, Fe/Co/Mg/MgO and Fe/Co/MgO/Mg contacts. Although a highly efficient spin injection has been reported by insertion of a thin Mg layer below or above the MgO layer, these thermal tolerances decrease obviously.

Improvement in the thermal tolerance of Si-based spin devices is realized by employing thermally stable nonmagnetic (NM) electrodes. For Au/Ta/Al electrodes, intermixing between Al atoms and Au atoms occurs at approximately 300°C, resulting in the formation of a Au/Si interface. The Au-Si liquid phase is formed and diffuses mainly along an in-plane direction between the Si and AlN capping layers, eventually breaking the MgO layer of the ferromagnetic (FM) metal/MgO electrodes, which is located 7 mm away from the NM electrodes. By changing the layer structure of the NM electrode from Au/Ta/Al to Au/Ta, the thermal tolerance is clearly enhanced. Clear spin transport signals are obtained even after annealing at 400°C. To investigate the effects of Mg insertion in FM electrodes on thermal tolerance, we also compare the thermal tolerance among Fe/Co/MgO, Fe/Co/Mg/MgO and Fe/Co/MgO/Mg contacts. Although a highly efficient spin injection has been reported by insertion of a thin Mg layer below or above the MgO layer, these thermal tolerances decrease obviously.

The spin-orbit interaction (SOI), as a manifestation of a relativistic effect in solids, has been attracting great attention in condensed matter physics because of its abundant nature for manipulating and/or converting a spin degree of freedom. Compound materials with bulk inversion symmetry breaking (GaAs, BiTeI, NbSe2…), heterostructures consisting of the aforementioned materials (InGaAs/InAlAs, Bi/Ag…) and single heavy elements (Pt, W, Ta, Bi…) are pivotal material systems for generating strong Dresselhaus- and Rashba-type SOI and for shedding light on a wide variety of modern physics such as two-dimensional materials science, superconductivity, magnetoelectrics, spintronics etc. Consequently, however, light elements and materials with bulk inversion symmetry have been outside the scope of the quest for SOI in solids. In this work, we show that a Si metal-oxide-semiconductor (MOS) is a new material stage possessing Rashba-type SOI, although Si is a light element and has lattice inversion symmetry resulting in inherently negligible SOI in bulk form. A strong gate electric field is applied to the Si MOS, and unexpectedly, we observe spin precession of propagating spins in the Si through the formation of an emergent effective magnetic field due to the SOI in the Si MOS. Furthermore, the Rashba parameter α in the system increases linearly up to 9.8×10−16 eV∙m for a gate electric field of 0.5 V/nm, i.e., it is gate tuneable, and the spin splitting Δ0 (= 0.6 μeV) is equivalent to that in strained GaAs. This finding is a successful establishment of a synthetic Rashba system using a ubiquitous light element with bulk inversion symmetry and pioneers a new family of SOI systems.

To augment the magnetoresistance (MR) ratio of n-type non-degenerate Si-based lateral spin valves (Si-LSVs), we modify the doping profile in the Si layer and introduce a larger local strain into the Si channel by changing a capping insulator. The highest MR ratio of 1.4% is achieved in the Si-LSVs through these improvements, with significant roles played by a reduction in the resistance-area product of the ferromagnetic contacts and an enhancement of the momentum relaxation time in the Si channel., 14 pages, 4 figures

The fabrication of a skyrmion circuit which stabilizes skyrmions is important to realize micro- to nano-sized skyrmion devices. One example of promising skyrmion-based device is Brownian computers, which have been theoretically proposed, but not realized. It would require a skyrmion circuit in which the skyrmion is stabilized and easily movable. However, the usual skyrmion circuits fabricated by etching of the ferromagnetic film decrease the demagnetization field stabilizing the skyrmions, and thus prevent their formation. In this study, a skyrmion Brownian circuit implemented in a continuous ferromagnetic film with patterned SiO$_2$ capping to stabilize the skyrmion formation. The patterned SiO$_2$ capping controls the saturation field of the ferromagnetic layer and forms a wire-shaped skyrmion potential well, which stabilizes skyrmion formation in the circuit. Moreover, we implement a hub (Y-junction) circuit without pinning sites at the junction by patterned SiO$_2$ capping. This technique enables the efficient control of skyrmion-based memory and logic devices, as well as Brownian computers., Comment: 9 pages, 6 figures

Voltage-controlled magnetic anisotropy (VCMA) in an atomically thin Ni film placed at an epitaxial Fe-MgO interface has been studied. We characterize the VCMA by employing Fe/Ni/MgO-based magnetic tunnel junction. Moreover, we conduct x-ray magnetic circular dichroism (XMCD) spectroscopy around Ni absorption edges under an external voltage application to the tunnel junction device. This operando XMCD spectroscopy demonstrates voltage-induced changes of orbital and effective spin magnetic moments of Ni. As compared with the previous study, where operando XMCD spectroscopy was performed on an atomically thin Co film, we find that the magnitude of the VCMA effect in Ni and Co is proportional to the voltage-induced change of the orbital magnetic moment. This study would lead to a comprehensive understanding of how an electric field affects interfacial magnetism in ferromagnetic metals.

Bolometers are rectification devices that convert electromagnetic waves into direct current voltage through a temperature change. A superconducting bolometer has a responsivity of approximately 106–107 V/W under cryogenic temperatures at infrared wavelengths; however, no devices have realized such a high responsivity in the sub-GHz frequency region. We describe a spin bolometer with a responsivity of (4.40 ± 0.04) × 106 V/W in the sub-GHz region at room temperature using heat generated in magnetic tunnel junctions through auto-oscillation. We attribute the unexpectedly high responsivity to a heat-induced spin-torque. This spin-torque modulates and synchronizes the magnetization precession due to the spin-torque auto-oscillation and produces a large voltage output. In our device, heat-induced spin-torque was obtained because of a large heat-controlled magnetic anisotropy change: −2.7 µJ/Wm, which is significant for enhancing dynamic range and responsivity. This study can potentially lead to the development of highly sensitive microwave detectors in the sub-GHz region., Goto et al present a bolometer based around the heat generation in magnetic tunnel junctions under auto-oscillation conditions. Unlike superconducting bolometers, the presented device operates at room temperature and sub-GHz frequencies, opening possibilities for use in microwave devices.

The argan tree, Argania spinosa, is only endemic to south-western Morocco. Oils from the argan tree are not only edible, but also used for hair-conditioning, dermocosmetic, and pharmaceutical purposes. The mechanical press method yields approximately 43% argan oil, and a residue, which is called the argan press cake (APC). To elucidate the usefulness of the APC, the effects of fermentation using the bacteria Lactobacillus plantarum Argan-L1, which is isolated from argan fruits, on the in vitro antioxidant properties of a 5% w/v APC-suspension (APC-S), were determined. The main sugar in the APC-S was sucrose, which was converted to lactic acid in the fermented APC-S (F-APC-S). Although the fermentation slightly reduced the phenolic compound content and Fe-reducing power, there was a notable rise in the superoxide anion (O2−) radical scavenging capacity in the F-APC-S. From the results obtained for the ultrafiltered fractions, it can be said that the increase in the O2− radical-scavenging capacity might be due to the presence of

We have investigated an analytic formula of the 1-dimensional magnetic skyrmion dynamics under external magnetic field gradient. We find excellent agreement between the analytical model and micromagnetic simulation results for various magnetic parameters such as the magnetic field gradient, Gilbert damping constant. We also observe much faster velocity of the chiral domain wall (DW) motion. The chiral DW is exist with smaller interfacial Dzyaloshinskii-Moriya interaction energy density cases. These results provide to develop efficient control of skyrmion for spintronic devices., 15 pages, 5 figures, 1 table

Room-temperature operation of a spin exclusive-or (xor) gate is demonstrated in lateral spin-valve devices with nondegenerate silicon ($\mathrm{Si}$) channels. The spin xor gate is a fundamental part of the magnetologic gate that enables reconfigurable and nonvolatile nand or or operation in one device. The device for the spin xor gate consists of three iron ($\mathrm{Fe}$)/cobalt ($\mathrm{Co}$)/magnesium oxide ($\mathrm{Mg}\mathrm{O}$) electrodes (i.e., two input electrodes and one output electrode). Spins whose spin angular momentum corresponds to the binary input 1 or 0 are injected into the $\mathrm{Si}$ channel from the input electrodes. The spin-drift effect is controlled by a lateral electric field in the $\mathrm{Si}$ channel to adjust the spin-accumulation voltages under two different parallel configurations, corresponding to (1, 1) and (0, 0), so that they exhibit the same value. As a result, the spin-accumulation voltage detected by the output electrode exhibits three different voltages, represented by an xor gate. The one-dimensional spin-drift--spin-diffusion model clearly explains the xor behavior obtained. Charge-current detection of the spin xor gate is also demonstrated. The detected charge current has a maximum of 1.67 nA, the highest value in spin xor gates reported thus far. Furthermore, gate-voltage modulation of the spin xor gate is also demonstrated, which enables operation of multiple magnetologic gate devices.

In this study, bi-stable toggle magnetization switching in magnetic tunnel junctions induced by electrically injected sub-nanosecond unipolar heat pulses was demonstrated. The switching probability of magnetization between bi-stable states was estimated by applying 0.5 ns voltage pulses and measuring the perpendicular component of the magnetization direction. The maximum switching probability was approximately 70%, suggesting that bi-stable toggle magnetization switching was induced by the torque created by the Joule-heat-induced magnetic anisotropy change. Joule-heat-driven magnetization switching has the potential to become a fundamental technology for fast spin control.

The detailed characteristics of magnetization switching in MgO-based magnetic tunnel junctions (MTJs) of diameters in the range of 21–57 nm with perpendicular magnetization are investigated by using pulses of durations in the range of 1–30 ns. Periodic fluctuations in the switching probability are observed at room temperature as a function of the biasing voltage. The period of the fluctuations is about 20–80 mV. The periods are in the same energy range as magnon excitations observed in tunnel spectroscopy. These fluctuations may also occur if there is a preferential trajectory in the free layer magnetization when it transverses the equator, as has been noted for in-plane magnetized MTJs. This kind of detailed observation of the switching probability may provide novel information about the switching dynamics.

We investigated the heat controlled magnetic anisotropy (HCMA) in magnetic tunnel junctions with various junction sizes. We evaluated the HCMA from perpendicular magnetic anisotropy under a direct current voltage measured by the spin-torque diode technique. The maximum HCMA magnitude of 5.4 μJ (Wm)−1 was observed, and the HCMA increased with increasing diameter. Our results can be explained by a simple heat dissipation model and suggest that the in-plane heat current affects HCMA.

Magnetic skyrmions are topological spin textures that have attracted significant attention owing to their diverse physical characteristics. Recently, various applications utilizing the Brownian motion of skyrmions have been reported. However, the diffusion of skyrmions is suppressed by pinning sites in magnetic thin films, which can limit computing speed. In this paper, we explore the stochastic dynamics and diffusion coefficient of skyrmions under a perpendicular alternating current (AC) magnetic field. The skyrmion diffusion coefficient increased exponentially as the AC magnetic field was increased owing to the stretching motion of the string-shaped skyrmions. This study may provide a technological framework for the realization of low-power-consumption Brownian devices.

Electric fields at interfaces exhibit useful phenomena, such as switching functions in transistors, through electron accumulations and/or electric dipole inductions. We find one potentially unique situation in a metal–dielectric interface in which the electric field is atomically inhomogeneous because of the strong electrostatic screening effect in metals. Such electric fields enable us to access electric quadrupoles of the electron shell. Here we show, by synchrotron X-ray absorption spectroscopy, electric field induction of magnetic dipole moments in a platinum monatomic layer placed on ferromagnetic iron. Our theoretical analysis indicates that electric quadrupole induction produces magnetic dipole moments and provides a large magnetic anisotropy change. In contrast with the inability of current designs to offer ultrahigh-density memory devices using electric-field-induced spin control, our findings enable a material design showing more than ten times larger anisotropy energy change for such a use and highlight a path in electric-field control of condensed matter., Electric field control of magnetization is usually weak and this hampers its application for the ultralow-power-consumption spintronic devices. Here, the authors demonstrate a mechanism to enhance the control of magnetic anisotropy by voltage-induced electric quadrupole in a metal–dielectric interface.

A gate voltage application in a Si-based spin metal-oxide-semiconductor field-effect transistor (spin MOSFET) modulates spin accumulation voltages, where both electrical conductivity and drift velocity are modified while keeping constant electric current. An unprecedented reduction in the spin accumulation voltages in a Si spin MOSFET under negative gate voltage applications is observed in a high electric bias current regime. To support our claim, the electric bias current dependence of the spin accumulation voltage under the gate voltage applications is investigated in detail and compared to a spin drift diffusion model including the conductance mismatch effect. We proved that the drastic decrease of the mobility and spin lifetime in the Si channel is due to the optical phonon emission at the high electric bias current, which consequently reduced the spin accumulation voltage., 14 pages, 4 figures

In this study, we fed ICR mice with a high-sucrose diet containing 20% w/w of milk-casein (MC), egg-white (EW), or soy-protein (SP) for 14 days in order to detect the presence of protein-susceptible gut indigenous bacteria (P-SIB). The caecal microbiome was examined by 16S rDNA amplicon sequencing using a next-generation MiSeq system. Principal coordinate analysis of the operational taxonomic units (OTUs) revealed that the microbiomes differed among the three groups. Typical SIB found in the MC-fed group were Bacteroides acidifaciens-, Bacteroides sartorii-, Eisenbergiella sp., and Lachnospiraceae sp.-like; in the EW-fed group were Lactobacillus murinus and Enterococcus faecium/avium-like; and in the SP-fed group were Muribaculaceae sp.-like bacteria. We also found that a few Lachnospiraceae sp.- and Clostridium disporicum-like bacteria were suppressed in the EW-fed mice. Out of the P-SIB detected, B. acidifaciens, L. murinus, E. faecium, and E. avium could be isolated and identified using BL agar and 16S rDNA BLAST search, respectively.

The FeIr/MgO multilayer system was found to exhibit large interfacial perpendicular magnetic anisotropy (PMA) and voltage-controlled magnetic anisotropy effects. We herein report the x-ray magnetic circular dichroism spectroscopy of both the Fe and Ir absorption edges in the FeIr/MgO system. Although Ir insertion at the Fe/MgO interface increased the PMA energy in the system, the orbital magnetic-moment anisotropy of Fe remained approximately constant. We found significant anisotropy in the orbital magnetic moment but not in the magnetic-dipole ${T}_{\mathrm{z}}$ term in the Ir atoms. Our experimental and theoretical results demonstrated that the large PMA of FeIr/MgO originates from second-order perturbation of the spin-orbit interaction energy of Ir. Moreover, the energy mainly originates from the spin-conserved virtual excitation process terms from the majority-spin bands of the Ir atoms located in the second atomic layer from MgO.

In this study, we investigated the interaction between skyrmions in Brownian motion at room-temperature. Cells containing two skyrmions were implemented by controlling the magnetic anisotropy in the Ta/CoFeB/Ta/MgO/SiO2 structure. The interaction between skyrmions was investigated by fabricating a circuit with two cells in close proximity to each other. It was found that the minimum value of the correlation coefficient was −0.234. These results show that the Brownian motion of skyrmions can potentially realize unconventional computing such as stochastic calculations and ultra-low power computing.

Magnetic skyrmions, which are topologically protected particle-like spin textures, exhibit Brownian motion at ambient temperatures in a ferromagnetic thin film. The potential applications of a skyr...

Quasi-maser operations using magnetic tunnel junctions (MTJs) that amplified the transmission of radio frequency (RF) signals through themselves are demonstrated. We measured the transmittance of heat-driven MTJs using a vector network analyzer and observed that transmittance S21 >1 at sub-GHz frequencies. Furthermore, we installed two of these MTJs in a feedback-loop circuit and investigated the RF signal in the circuit. The results showed that the auto-oscillation mode of the RF signal appeared without phase synchronization of each MTJ because of the amplification effect. Our results will help develop a mechanism for producing coherent microwave signals using multiple MTJs.

We propose the use of artificial spin ice (ASI) for reservoir computing and evaluate its performance from simulation results. Our ASI reservoir is formed by 72 magnets arranged in a honeycomb lattice and the temperature is 0 K. A pseudo-random binary sequence is sent to the reservoir and its status is updated by external magnetic fields. Short-term memory capacity of 3.5 and nonlinear computational capacity of 2.9 are achieved when the strength of the magnetic fields is near the switching field of the magnets. The performance can be optimized by tuning the aspect ratios of the magnets.

Magnetic tunnel junctions (MTJs) have been identified as promising candidates for the development of high-performance, ultra-low field magnetometers due to their high sensitivity, low cost, low power consumption, and small size. However, 1/f noise is often quite large at low frequencies and inevitably becomes one of the most difficult issues in developing a magnetic field sensor with ultrahigh sensitivity. Low-frequency 1/f noise can have both electric and magnetic origins, and it is a result of complex non-linear interactions between many degrees of freedom inside a sensor. Therefore, a reduction of the 1/f noise can be expected for the magnetic sensor with very small dimensions. Here, the dependence of the 1/f noise on voltage and strong hard-axis bias field in deep submicrometer-sized MgO-based MTJs is investigated with various junction sizes. The noise spectra were measured by using a home-built low-frequency noise measurement setup with maximum frequency up to 30 kHz. We find that the noise spectral power density is 1/f-like at low frequencies. The experimental results suggest a relative reduction of 1/f noise with respect to the intrinsic thermal noise in small-sized MTJs. The results may open a new approach for reducing the 1/f noise level in MTJ nanosensors.

The effect of thermal annealing on spin accumulation signals in silicon (Si)-based lateral spin devices is investigated. The annealing is carried out after fabrication of the spin devices, which allows us to directly compare the spin-related phenomena before and after annealing. The magnitude of non-local four-terminal signals (ΔVnl) at room temperature is increased more than two-fold after annealing at 300 °C for 1 h. The channel length dependence of ΔVnl and the Hanle signals reveal that the spin polarization of the ferromagnetic contact is increased by the annealing. In contrast, the spin diffusion length and spin lifetime in the Si channel do not change.

We studied nonlinear magnetic anisotropy changes to the DC bias voltage of magnetic tunnel junctions (MTJs) with capping layers of different thermal resistances. We found that increasing the thickness of MgO capping layers (in the range 0.3-0.5 nm) in MTJs enhances the Joule heating-induced magnetic anisotropy change, which indicates an enhancement of the interfacial thermal resistance at the FeB|MgO capping layer interface. This enhanced interfacial thermal resistance may be attributed to roughness at the FeB|MgO interface. Moreover, we observed a larger power-driven magnetic anisotropy change of 3.21 µJ W-1m-1 in the MTJ with a composite MgO (0.3 nm)|W (2 nm)|MgO (0.4 nm) capping layer. This research supports methods of efficient spin manipulation of spintronic devices such as microwave devices and magnetic memories.

We fabricated epitaxial multilayers with Co and Pd atomic-layer insertion at Fe(001)/MgO(001) interface and systematically investigated voltage-controlled magnetic anisotropy (VCMA) and voltage-induced interfacial Dzyaloshinskii-Moriya interaction $(i\mathrm{DMI})$ change. The VCMA and $i\mathrm{DMI}$ change was characterized by spin-wave spectroscopy. We found that the VCMA was increased by Co and Pd insertions to \ensuremath{-}180 fJ/Vm in the Fe/Co/Pd/MgO system. We also found a large voltage-induced $i\mathrm{DMI}$ change of 65 fJ/Vm. The postannealing dependence of the VCMA and $i\mathrm{DMI}$ change was also characterized to investigate the influence of the change in chemical ordering around the MgO interface.

Voltage-controlled magnetic anisotropy (VCMA) in an epitaxially grown Fe/Fe1−xCox/Pd/MgO system was investigated using spin-wave spectroscopy. The spin-wave resonant frequency linearly depended on the bias-voltage. The resonant-frequency shift increased with the Co fraction in Fe1−xCox/Pd. We achieved a VCMA of approximately 250 fJ/Vm at the Co/Pd/MgO region.

Heat-driven engines are hard to realize in nanoscale machines because of efficient heat dissipation1. However, in the realm of spintronics, heat has been employed successfully—for example, heat current has been converted into a spin current in a NiFe|Pt bilayer system2, and Joule heating has enabled selective writing in magnetic memory arrays3. Here, we use Joule heating in nanoscale magnetic tunnel junctions to create a giant spin torque due to a magnetic anisotropy change. Efficient conversion from heat dynamics to spin dynamics is obtained because of a large interfacial thermal resistance at an FeB|MgO interface. The heat-driven spin torque is equivalent to a voltage-controlled magnetic anisotropy4,5 of approximately 300 fJ V−1 m−1, which is more than twice the value reported in a (Co)FeB|MgO system6,7. We demonstrate an electric microwave amplification gain of 20% in a d.c. biased magnetic tunnel junction as a result of this spin torque. While electric d.c. power amplification in spintronic devices has been realized previously8, the microwave amplification was limited to relatively small amplification gains (G = radiofrequency output voltage/radiofrequency input voltage) and has never exceeded 1 (refs 9–13). A magnetic tunnel junction driven by radiofrequency spin transfer torque using ferromagnetic resonance enabled a relatively large gain of G ≈ 0.55 (ref. 12). Furthermore, radiofrequency spin waves were tuned by the spin transfer effect14,15. The heat-driven giant spin torque in the FeB|MgO16,17 magnetic tunnel junction, which shows a large magnetization precession and resistance oscillation under a d.c. bias, overcomes the above limitations and provides a gain larger than 1. Joule heating in a d.c. biased magnetic tunnel junction provides giant spin torque which amplifies an electric microwave applied to the device.

In this work we report observation of in-plane current induced out-of-plane magnetic field driven torque in spin valve structure. Since ferromagnet has high spin orbit coupling it is expected to be the source of spin-orbit-torque as it possesses anomalous-Hall-effect (AHE: equivalent to spin Hall effect in heavy metal). So we have carried out spin-torque ferromagnetic resonance (ST-FMR) experiment in a spin valve (consists of a fixed magnet and a free magnet which are separated by Cu spacer), passing in-plane radio frequency current and measuring DC voltage. Our experimental results eventually indicate that spin torque exerted on the free magnet is not caused due to the spin current injection by the fixed magnet owing to its AHE, but it is originated from in-plane current driven out-of plane effective magnetic field. This is new class of spin torque which is completely different from Slonczewski-spin transfer torque and Rashba like field like torque. The effective out-of plane magnetic field depends on the direction of current (in-plane) and magnetization (in-plane) of the pinned layer. One possible mechanism behind this unconventional torque could be intefacial spin-scattering which is also origin of current in-plane GMR effect. Most importantly this effective out-of plane torque can be useful to switch out-of plane magnetic bits in spintronic memory application.

Torque can be provided to magnetization in nanomagnets directly by electric current and/or voltage. This technique enables electric current (voltage)-to-spin conversion without electromagnetic induction, and has been intensively studied for memory device applications. Among the various kinds of torque, torque induced by spin-orbit splitting has recently been found. However, quantitative understanding of bulk-related torque and interface-related torque is still lacking because of their identical symmetry for current-in-plane devices. In this paper, we propose that a pure interface-related torque can be characterized by spin-torque ferromagnetic resonance with a current-perpendicular-to-plane tunnel junction. Epitaxial Fe-MgO-V tunnel junctions are prepared to characterize the interface-related torque at Fe-MgO. We find that the current-driven torque is negligible, and a significant enhancement of the voltage-driven torque is observed when the MgO barrier thickness decreases. The maximum torque obtained is as large as 2.8×10^{−5} J/(Vm^{2}), which is comparable to the voltage-controlled magnetic anisotropy of 180 fJ/Vm. The voltage-driven torque shows strong dc-bias-voltage dependence that cannot be explained by conventional voltage-controlled magnetic anisotropy. Tunnel anisotropic magnetoresistance spectroscopy suggests that the torque is correlated to an interface state at the Fe-MgO. This surface-state-sensitive electric modulation of magnetic properties provides new insight into the field of interface magnetism.

Reservoir computing (RC), which utilizes physical phenomena, is a candidate for low energy consumption recurrent neural networks. Recently, we proposed RC which uses a dipole-coupled nanomagnet array as a reservoir, which applies the direction of the static magnetic moment of each nanomagnet as a node state in the array. It is possible to learn binary tasks with one-bit input data using this reservoir. Moreover, more complex tasks such as motion detection utilize multi-bit input data. This study simulates a two-bit binary input RC by employing the dipole coupled nanomagnet array as a reservoir. We apply a binary task with two-bit input data, which requires a memory capacity and non-linear computing capability of the reservoir. Due to the simulations with a macrospin model at a temperature of 0 K, this RC was able to learn these binary tasks by utilizing 24 nanomagnets.