A5034930944- Magnetic properties of thin films
- Magnetic Properties and Applications
- Magnetic and transport properties of perovskites and related materials
- ZnO doping and properties
- Multiferroics and related materials
- Metallic Glasses and Amorphous Alloys
- Physics of Superconductivity and Magnetism
- Quantum and electron transport phenomena
- Theoretical and Computational Physics
- Metal and Thin Film Mechanics
- Magnetic Properties of Alloys
- Advanced Memory and Neural Computing
- Advanced Condensed Matter Physics
- Magneto-Optical Properties and Applications
- Electronic and Structural Properties of Oxides
- Advanced Electron Microscopy Techniques and Applications
- Copper Interconnects and Reliability
- Electron and X-Ray Spectroscopy Techniques
- Mechanical and Optical Resonators
- Nanoporous metals and alloys
- Copper-based nanomaterials and applications
- Nuclear Physics and Applications
- Mineralogy and Gemology Studies
- Transition Metal Oxide Nanomaterials
- Electrochemical Analysis and Applications
National Institute of Advanced Industrial Science and Technology
2010-2023
Japan Science and Technology Agency
2004-2013
Prokhorov General Physics Institute
2011
Tohoku University
1997-2005
We fabricated a spin-torque oscillator (STO) having nanopillar-shaped magnetic tunnel junction with perpendicularly magnetized FeB free and in-plane CoFeB reference layers. The perpendicular magnetization of the was stabilized by strong anisotropy induced at both MgO barrier/FeB FeB/MgO cap interfaces. Under field (3 kOe), STO exhibited large emission power (0.55 µW), high frequency (6.3 GHz) Q factor (135) simultaneously, all which are largest to date among STOs. bias voltage dependence...
We developed top-free-type perpendicularly magnetized magnetic tunnel junctions (p-MTJs) with a synthetic antiferromagnetic (SAF) bottom reference layer consisting of [Co/Pt] superlattice and Ru spacer layers. successfully demonstrated practical properties such as low resistance–area (RA) product (<3 Ω µm2), ultralow writing voltage (<200 mV) for spin-transfer-torque (STT) switching, high annealing stability (up to 350 °C) in the same p-MTJ cells. Moreover, p-MTJs showed clear bi-stable...
We investigated the voltage-controlled magnetic anisotropy (VCMA) in an ultrathin Ir-doped Fe layer with a CoxFe1−x termination layer. The VCMA effect depends on concentration of alloy, and large coefficient, as high −350 fJ/Vm, was obtained Co-rich First principles calculations revealed that increased is due not only to added Co atoms but also Ir adjacent atoms. Interface engineering using CoFe effective for recovering tunneling magnetoresistance while maintaining effect. developed...
Microwave oscillation properties of spin torque vortex oscillators (STVOs) consisting an FeB free layer were investigated. Because a high MR ratio and large DC current, emission power up to 3.6 µW was attained in the STVO with thin 3 nm. In STOs thicker layer, e.g., 10 nm thick, we obtained Q factor greater than 6400 while maintaining integrated 1.4 µW. Such excellent microwave performance is breakthrough for mutual phase locking STVOs by electrical coupling.
Phase locking experiments on vortex based spin transfer oscillators with an external microwave current are realized. We present clear evidence of synchronization, i.e., phase locking, frequency pulling, as well fractional synchronization in this system a minimum peak linewidth only 3 kHz the locked state. Large ranges achieved (up to 1/3 oscillator frequency) allowing us demonstrate simultaneous two independent connected series source.
We investigated the effect of voltage on perpendicular magnetic anisotropy in an ultrathin Fe80B20 layer sandwiched between two MgO barrier layers with different thicknesses, which bias is predominantly applied to one layers. The application both positive and negative voltages enhanced anisotropy, contrast odd function dependence previously observed a MgO/ferromagnetic metal/non-magnetic metal structure. Moreover, for voltages, large change slope 108 fJ/Vm was demonstrated. These results...
This paper presents a review and future prospects for the tunnel magnetoresistance (TMR) effect in magnetic junction (MTJ) spin manipulation technologies such as spin-transfer torque (STT) magnetoresistive random access memory (MRAM). Major challenges ultrahigh-density STT-MRAM with perpendicular magnetization novel functional devices related to MRAM are discussed.
We investigated the Gilbert damping of thin films with a MgO-barrier/Fe80B20/MgO-cap/Ta structure, in which Fe80B20 layer corresponds to free perpendicularly magnetized magnetic tunnel junction, by using ferromagnetic resonance (FMR). systematically varied thickness MgO cap and estimated constant (α) measuring dependence FMR spectrum on field angle. The was found reduce α about 0.005, is less than half value without cap. significant reduction can be explained suppression spin pumping...
We systematically investigated the Gilbert damping (α) and interfacial perpendicular magnetic anisotropy (Ki) in tunnel junctions with a MgO-barrier/FeB/MgO-cap layered structure using spin-torque diode effect. By increasing MgO cap thickness, α decreased, whereas Ki increased monotonically. Values down to 0.0054 for up 3.3 erg/cm2 were obtained thickness of 0.6 nm. The small large suggest that MgO-capped FeB is suitable free layer spintronics devices such as oscillators random access memories.
Abstract Perpendicular magnetic anisotropy (PMA) is becoming increasingly important in spintronics research, especially for high-density magnetoresistive random access memories (MRAMs). The PMA induced at an Fe/MgO interface widely used tunnel junctions. Here, we propose inserting ultrathin LiF layer the epitaxial junction. With a 0.3 nm-thick layer, large intrinsic energy, K i ,0 , of 2.8 mJ/m 2 was achieved. We also found that LiF/MgO bilayer tunneling barrier exhibited magnetoresistance...
Abstract We deposited an ultrathin CoFeB(1.1 nm) layer, which functions as a storage layer of MgO-based magnetic tunnel junctions for spin-transfer-torque (STT) magnetoresistive random-access memory (MRAM), on ϕ 300 mm wafers at 100 K and investigated its effect the magnetization dynamics CoFeB. observed clear reductions in both inhomogeneous linewidth total damping parameter CoFeB compared to those through improvement interfacial quality. The results show that deposition cryogenic...
We developed a cryogenic temperature deposition process for high-performance CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) on ϕ300 mm thermally oxidized silicon wafers. The effect of the CoFeB layers nanostructure, magnetic, and magneto-transport properties MTJs was investigated in detail. When deposited at 100 K, exhibited perpendicular anisotropy (PMA) 214 μJ/m2 voltage-controlled (VCMA) coefficient −45 fJ/V m, corresponding to 1.4- 1.7-fold enhancements PMA VCMA, respectively, compared...
We have succeeded in developing highly ordered magnetic vortices dense arrays of microstructured magnets and evaluating individual spin configuration by employing a high-precision spin-imaging technique. High-definition pictures reveal fundamental properties the vortices, such as stability interaction vortex chirality. also demonstrated control chirality with use field gradient but without introducing geometric asymmetry magnet shape. A simple mechanism is deduced from micromagnetic simulations.
We have developed spin-polarized scanning electron microscopy (spin SEM) with a 5-nm resolution. The secondary optics is very important, as it needs to transfer sufficient number of electrons the spin polarimeter, due low efficiency polarimeter. was designed using three-dimensional (3D) simulation program trajectories, and achieves highly efficient collection transport even though distance between sample objective lens exit gun remains short. Moreover, enables us obtain clear SEM images in...
Three-dimensional colloidal crystals made of ferromagnetic particles, such as magnetite (Fe(3)O(4)), cannot be synthesized in principle because the strong attractive magnetic interaction. However, we discovered composed polyhedral nanocrystallites uniform size range a few hundred nanometers Tagish Lake meteorite. Those were formed 4.6 billion years ago and thus are much older than natural on earth, opals, which about 100 million ago. We found that each individual particle determines its...
With the use of a newly developed spin-polarized scanning electron microscope, we have succeeded in obtaining real-space images layered-antiferromagnetic state concurrent with 1-nm-stepped atomic terraces layered-structure manganite $\mathrm{L}{\mathrm{a}}_{\mathrm{1.4}}\mathrm{S}{\mathrm{r}}_{\mathrm{1.6}}\mathrm{M}{\mathrm{n}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{7}}$. The three-dimensional analysis spin alignment could further reveal temperature-dependent reorientation and anfiferromagnetic...
We report on the oscillation behavior of spin torque oscillators having a perpendicularly magnetized free layer and in-plane reference as function bias field angle. The measurement results show that both emission power frequency are strongly dependent When was tilted by only few degrees away from axis normal to film toward either parallel or antiparallel configuration, increased about 1.5 times decreased two orders magnitude, peak varied ±1 GHz.
Improving the perpendicular magnetic anisotropy (PMA) and voltage-controlled (VCMA) properties are fundamentally important for development of magnetoresistive random access memories (VC-MRAM). Recently, we reported on a large increase in PMA at an Fe/MgO interface brought about by inserting ultrathin LiF layer interface. In this paper, investigate PMA, VCMA, TMR MTJs with Ir-doped ferromagnetic LiF/MgO hybrid tunneling barrier. We observed clear interfacial factor 2.5 when 0.25 nm was...
Measurements of thermally excited ferromagnetic resonance were performed on spin torque oscillators having a perpendicularly magnetized free layer and in-plane reference (abbreviated as PMF-STO in the following) for purpose obtaining magnetic properties structure. The measured spectra clearly showed large main peak multiple smaller peaks high frequency side. A Lorentzian fit yielded Gilbert damping factor 0.0041. observed moved proportion to out-of-plane bias field. From slope function...
Abstract The voltage-controlled magnetic anisotropy (VCMA) effect is a key to realising high-speed, ultralow-power consumption spintronic devices. fcc-Co-(111)-based stack promising candidate for the achievement of large VCMA coefficients. However, only few studies on have been reported and has not well understood. Previously, we observed significant increase in coercivity (VCC) Pt/Ru/Co/CoO/TiO x structure upon post-annealing. mechanism underlying this enhancement remains unclear. This...
The magnetization vector distribution at a cleaved surface of La0.7Sr0.3MnO3 (001) crystal has been quantitatively analyzed by using newly developed low-temperature spin-polarized scanning electron microscope. magnetic structure essentially consists two kinds domains, where magnetizations are parallel or antiparallel to the [110] direction with no surface-normal component. rhombus-shaped domains range from few several tens micrometers across. domain can be considered made laying down...
The spin structures of vortex domain walls forming in a ferromagnetic ${\text{La}}_{0.6}{\text{Sr}}_{0.4}{\text{MnO}}_{3}$ nanowire have been directly observed using Lorentz microscopy. We visualized the in-plane anisotropic structures, which exhibited twofold rotational symmetry and revealed that simultaneous reversal chirality magnetization directions separated domains occurs at all pinning sites. observations indicate is determined by magnetic anisotropy induced