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Skyrmions are topological spin textures that exhibit Brownian motion in solids. They have attracted increasing research interest in terms of realizing a device that utilizing stochastic behavior and investigating new physical phenomena. However, skyrmions that exhibit Brownian motion are sensitive to changes in magnetic properties and are easily affected by aging variation. For instance, although skyrmions appear in a sample immediately after fabrication, they sometimes disappear after few weeks. This characteristic prevents the reproducibility experiment and affects device stability. In this study, we demonstrated that aging variation can be suppressed by annealing in air for only 3 min, which is an easy and rapid method. We investigated the change in the magnetic properties by annealing and air exposure and found that the main mechanism of aging variation is oxidation of the sample surface. The magnetic properties of samples with Pt and thick SiO2 capping were analyzed, and we demonstrated that aging variation can be suppressed by avoiding surface oxidation. Our work accelerates the research of fundamental physics regarding skyrmion Brownian motion and of device applications utilizing stochastic system.

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.

We demonstrated a magnetic tunnel junction (MTJ) consisting of Fe/MgO-Si-MgO/Fe. Si layer was deposited at room temperature and at 700 °C; when deposited at 700 °C, Si diffused into the MgO layer. The MTJ with silicon deposited at 700 °C attained high MR ratios of up to 38.7 and 2.9% at t _Si = 0.19 and 1.3 nm, respectively. Low-temperature measurements established that the temperature dependence of the MR ratio and resistance between MTJs with and without diffused silicon are significantly different. This behavior confirms that the Si-MgO channel acts as an impurity semiconductor in the MTJ.

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.

We investigate stability of the spin exclusive or (XOR) gate operation in silicon(Si) -based lateral spin devices whose spin transport properties have large variations. The optimum charge current, I0, for the spin XOR gate operation is calculated by using the one dimensional spin-drift-diffusion model with variable spin polarization, interface resistance of the ferromagnetic contact, channel length and channel conductivity. I0 is strongly modulated by changing the spin transport parameters particularly under the condition with small spin polarization and short channel length. In contrast, I0 shows constant value irrespective of the interface resistance of one ferromagnetic contact under spin extraction condition. Our results provide a device design guideline for the robust spin XOR gate operation.

Some food ingredients are thought to be correlated with the gut microbiome. To clarify the presence of susceptible gut indigenous bacteria (SIB) against four popular spices, ICR mice were fed with a high-sucrose diet containing no-fibre (NF), 2% w/w cumin-seeds (CM), coriander-seeds (CR), turmeric (TM), or red chili pepper (RP) for seven days. The caecal microbiome was examined by 16S rDNA amplicon sequencing using a MiSeq system. Principal coordinate analysis of operational taxonomic units (OTUs) revealed microbiome alterations in the CM, CR, and RP groups. Typical SIB in the CM, CR, TM, and RP groups were Bacteroides acidifaciens- and Bacteroide sartorii-like, Lactobacillus johnsonii-like, Bifidobacterium pseudolongum-like, and RP-SIB Lactobacillus murinus--like bacteria, respectively. [Clostridium] innocuum- and Faecalibaculum rodentium-like bacteria were suppressed by the spices. Of the SIB identified, B. pseudolongum, L. johnsonii, L. murinus, and [Clostridium] innocuum were isolated and identified using BL agar and a 16S rDNA BLAST search, respectively.

We have investigated an approximated analytic form of the one-dimensional motion of skyrmions accelerated by a gradient of the external magnetic field. We find excellent agreement between the analytical calculations and micromagnetic simulations when the skyrmion size is large. The skyrmion motion is related to not only the skyrmion size but also the skyrmion wall width. We also have performed the numerical calculation without approximation in comparison. The numerical calculation results are entirely in agreement with those of micromagnetic simulation for all the skyrmion size. These results introduce an efficient control of skyrmions to next-generation spintronic devices.

We demonstrate the current-driven resonance of a single antivortex core confined in a cross-shaped Ni81Fe19 wire. The antivortex core dynamics can be excited purely by spin transfer torque; therefore, it is significant to understand the current-induced magnetization dynamics. The antivortex core resonance can be measured from the frequency dependence of a rectified voltage generated by an alternating current application. We found that the resonance frequency and peak amplitude greatly depend on the external magnetic field. This result is in good agreement with micromagnetic simulation.

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.

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 skyrmions' diffusive motion to the ultra-low energy stochastic and Brownian computation make research on its thermal dynamics necessary. Herein we experimentally demonstrate the mobility anomaly of the diffusion coefficients in one-dimensional diffusion processes. In addition, we observed a chiral property in the velocity-position correlation functions. The results are discussed in the context of Brownian motion in the shallow potential fluctuations. The data indicate the importance of the chiral property of skyrmions in Brownian motion. [ABSTRACT FROM AUTHOR]

In this study, voltage-controlled magnetic anisotropy (VCMA) in Fe|MgO tunnel junctions was investigated via the magneto-optical Kerr effect, soft x-ray absorption spectroscopy, and magnetic circular dichroism spectroscopy. The Fe|MgO tunnel junctions showed enhanced perpendicular magnetic anisotropy under external negative voltage, which induced charge depletion at the Fe|MgO interface. Despite the application of voltages of opposite polarity, no trace of chemical reaction such as a redox reaction attributed to O2- migration was detected in the x-ray absorption spectra of the Fe. The VCMA reported in the Fe|MgO-based magnetic tunnel junctions must therefore originate from phenomena associated with the purely electric effect, that is, surface electron doping and/or redistribution induced by an external electric field. [ABSTRACT FROM AUTHOR]

We demonstrate reservoir computing using a dipole-coupled magnetic-dot array by simulations with a macro-spin model at 0 K. The magnetic moment of the dot is used for the node state of the reservoir. We perform short-term-memory (STM) and parity check (PC) tasks to evaluate the performance of the reservoir. Binary information was written to the input magnetic dots as a direction of the magnetic moment. A voltage-induced magnetic-anisotropy change was used to update the node state. We investigated the STM capacity (STMC) and PC capacity (PCC) dependence on the number of magnetic dots by means of randomly generated node-update procedures. As a result, the STMC and PCC are strongly dependent on the node-state update procedure. [ABSTRACT FROM AUTHOR]

The feasibility of reservoir computing based on dipole-coupled nanomagnets is demonstrated using micro-magnetic simulations at 0 K. The static-magnetization directions of the nanomagnets are used as reservoir states. To update these states, we change the magnetization of one nanomagnet according to a single-bit-sequential input signal. We also change the uniaxial-anisotropy of the other nanomagnets using a voltage-induced magnetic anisotropy change to facilitate the flow of information, storage, and linear/nonlinear calculations. As a result, the reservoir computing output matrix was found to be trainable to perform AND/OR/XOR operations with an input delay of up to three bits. [ABSTRACT FROM AUTHOR]

A single-crystal multilayer consisting of Fe, cobalt phthalocyanine (CoPc), and MgO was grown on an fcc-MgO(001) substrate. The reflection high-energy diffraction observation showed that the ultrathin fcc-MgO(001) film could be grown on bcc-Fe(001)/CoPc when the thickness of CoPc was less than 0.7 nm (about two molecular layers). A tunnel junction with a bcc-Fe(001)/CoPc/fcc-MgO(001)/bcc-Fe(001) layer achieved a tunnel magnetoresistance of about 20% and an electric field endurance of more than 1 V/nm at room temperature. The novel multilayer in the present study will enable us to advance the frontiers of molecular spintronics. [ABSTRACT FROM AUTHOR]

The magnetic moments of a Pt|Fe(0.5 nm)|MgO film at an external electric field of in a 0.35 V/nm were characterized by analyzing the X-ray magnetic circular dichroism (XMCD) at the L-edges of Fe using a partial fluorescence yield method with a precision 40 times greater than that in our previous study. The XMCD induced by the electric field was negligible (<0.2%). Furthermore, although an induced orbital magnetic moment seemingly existed, it was within the precision error (0.3%). This paper demonstrates that slight electron doping and/or redistribution without any electrochemical reaction causes voltage-controlled magnetic anisotropy at Fe|MgO interfaces. [ABSTRACT FROM AUTHOR]

The voltage-controlled magnetic anisotropy of ferromagnetic metals may offer potential applications of nonvolatile memories with ultralow power consumption. For achieving ultrafast recording and long-time endurance, voltage-induced effects without undesirable lattice distortions should be ensured. In this study, in-situ extended X-ray absorption fine structure analysis of an Fe/Pt/MgO junction demonstrated the unaltered interfacial atomic structure, in which the radial distances between the Pt and the neighboring Fe, Pt, O, and Mg atoms changed by less than ±0.01 Å under electric fields of ±0.18 V/nm. Therefore, the anisotropy change is driven by a purely electronic mechanism without lattice deformation or atomic relaxation. [ABSTRACT FROM AUTHOR]

We present electric field modulation of tunneling anisotropic magnetoresistance (TAMR) in MnIr|MgO|Ta tunnel junctions. TAMR enables direct observation of the antiferromagnetic spin direction at the MnIr|MgO interface. We found that the shape of magnetoresistance (MR) curve can be modulated by an electric field, which can be explained by electric field modulation of the interfacial magnetic anisotropy at MnIr|MgO. [ABSTRACT FROM AUTHOR]

We demonstrate the time-resolved real-space observation of vortex gyration in a magnetic circular disc by X-ray magnetic circular dichroism photoemission microscopy at the SPring-8 beamline BL25SU, both with and without an additional structure called a pair tag, which serves to control the magnetic curling direction. By comparing the gyration orbits of the vortices, we found that the gyration properties are dependent on the presence of the additional structure in spite of the discs having the same diameter. Furthermore, we reproduced the vortex gyration by micromagnetic simulation. The confinement potential of the vortex can be controlled by the additional structure. [ABSTRACT FROM AUTHOR]

Antivortex creation in a cross-shaped wire was demonstrated by using magnetoresistance and magnetic force microscopy measurements. The magnetization process was stochastic and exhibited a wide variety of magnetoresistance curves. By developing a conventional method, we have achieved electrical determination criteria to distinguish antivortex creation from many other magnetization states. The electrical criteria provide a simple method without large-scale apparatus and promote further experiments such as spin-current driven antivortex dynamics. [ABSTRACT FROM AUTHOR]

In this study, the microscopic origins of the voltage-controlled magnetic anisotropy (VCMA) in 3d-ferromagnetic metals are revealed. Using in situ x-ray fluorescence spectroscopy that provides a high quantum efficiency, electric-field-induced changes in orbital magnetic moment and magnetic dipole Tz terms in ultrathin Co films are demonstrated. An orbital magnetic moment difference of 0.013µB was generated in the presence of electric fields of ±0.2V/nm. The VCMA of Co was properly estimated by the induced change in orbital magnetic moment, according to the perturbation theory model. The induced change in the magnetic dipole Tz term only slightly contributed to the VCMA in 3d-ferromagnetic metals. [ABSTRACT FROM AUTHOR]