Temporal pattern recognition with delayed feedback spin-torque nano-oscillators.

The recent demonstration of neuromorphic computing with spin-torque nano-oscillators has opened a path to energy efficient data processing. The success of this demonstration hinged on the intrinsic short-term memory of the oscillators. In this study, we extend the memory of the spin-torque nano-oscillators through time-delayed feedback. We leverage this extrinsic memory to increase the efficiency of solving pattern recognition tasks that require memory to discriminate different inputs. The large tunability of these non-linear oscillators allows us to control and optimize the delayed feedback memory using different operating conditions of applied current and magnetic field.

Vector network analyzer ferromagnetic resonance spectrometer with field differential detection.

This work presents a vector network analyzer ferromagnetic resonance (VNA-FMR) spectrometer with field differential detection. This technique differentiates the S-parameter by applying a small binary modulation field in addition to the DC bias field to the sample. By setting the modulation frequency sufficiently high, slow sensitivity fluctuations of the VNA, i.e., low-frequency components of the trace noise, which limit the signal-to-noise ratio of the conventional VNA-FMR spectrometer, can be effectively removed, resulting in a very clean FMR signal. This paper presents the details of the hardware implementation and measurement sequence as well as the data processing and analysis algorithms tailored for the FMR spectrum obtained with this technique. Because the VNA measures a complex S-parameter, it is possible to estimate the Gilbert damping parameter from the slope of the phase variation of the S-parameter with respect to the bias field. We show that this algorithm is more robust against noise than the conventional algorithm based on the linewidth.

Enhancement of perpendicular magnetic anisotropy and its electric field-induced change through interface engineering in Cr/Fe/MgO.

Recently, perpendicular magnetic anisotropy (PMA) and its voltage control (VC) was demonstrated for Cr/Fe/MgO. In this study, we shed light on the origin of large voltage-induced anisotropy change in Cr/Fe/MgO. Analysis of the chemical structure of Cr/Fe/MgO revealed the existence of Cr atoms in the proximity of the Fe/MgO interface, which can affect both magnetic anisotropy (MA) and its VC. We showed that PMA and its VC can be enhanced by controlled Cr doping at the Fe/MgO interface. For Cr/Fe (5.9 Å)/Cr (0.7 Å)/MgO with an effective PMA of 0.8 MJ/m3, a maximum value of the voltage-controlled magnetic anisotropy (VCMA) effect of 370 fJ/Vm was demonstrated due to Cr insertion.

Mutual synchronization of spin torque nano-oscillators through a long-range and tunable electrical coupling scheme.

The concept of spin-torque-driven high-frequency magnetization dynamics, allows the potential construction of complex networks of non-linear dynamical nanoscale systems, combining the field of spintronics and the study of non-linear systems. In the few previous demonstrations of synchronization of several spin-torque oscillators, the short-range nature of the magnetic coupling that was used has largely hampered a complete control of the synchronization process. Here we demonstrate the successful mutual synchronization of two spin-torque oscillators with a large separation distance through their long range self-emitted microwave currents. This leads to a strong improvement of both the emitted power and the linewidth. The full control of the synchronized state is achieved at the nanoscale through two active spin transfer torques, but also externally through an electrical delay line. These additional levels of control of the synchronization capability provide a new approach to develop spin-torque oscillator-based nanoscale microwave-devices going from microwave-sources to bio-inspired networks.

Neuromorphic Computing through Time-Multiplexing with a Spin-Torque Nano-Oscillator.

Fabricating powerful neuromorphic chips the size of a thumb requires miniaturizing their basic units: synapses and neurons. The challenge for neurons is to scale them down to submicrometer diameters while maintaining the properties that allow for reliable information processing: high signal to noise ratio, endurance, stability, reproducibility. In this work, we show that compact spin-torque nano-oscillators can naturally implement such neurons, and quantify their ability to realize an actual cognitive task. In particular, we show that they can naturally implement reservoir computing with high performance and detail the recipes for this capability.

Coherent microwave generation by spintronic feedback oscillator.

The transfer of spin angular momentum to a nanomagnet from a spin polarized current provides an efficient means of controlling the magnetization direction in nanomagnets. A unique consequence of this spin torque is that the spontaneous oscillations of the magnetization can be induced by applying a combination of a dc bias current and a magnetic field. Here we experimentally demonstrate a different effect, which can drive a nanomagnet into spontaneous oscillations without any need of spin torque. For the demonstration of this effect, we use a nano-pillar of magnetic tunnel junction (MTJ) powered by a dc current and connected to a coplanar waveguide (CPW) lying above the free layer of the MTJ. Any fluctuation of the free layer magnetization is converted into oscillating voltage via the tunneling magneto-resistance effect and is fed back into the MTJ by the CPW through inductive coupling. As a result of this feedback, the magnetization of the free layer can be driven into a continual precession. The combination of MTJ and CPW behaves similar to a laser system and outputs a stable rf power with quality factor exceeding 10,000.

Spin-torque resonant expulsion of the vortex core for an efficient radiofrequency detection scheme.

It has been proposed that high-frequency detectors based on the so-called spin-torque diode effect in spin transfer oscillators could eventually replace conventional Schottky diodes due to their nanoscale size, frequency tunability and large output sensitivity. Although a promising candidate for information and communications technology applications, the output voltage generated from this effect has still to be improved and, more pertinently, reduces drastically with decreasing radiofrequency (RF) current. Here we present a scheme for a new type of spintronics-based high-frequency detector based on the expulsion of the vortex core in a magnetic tunnel junction (MTJ). The resonant expulsion of the core leads to a large and sharp change in resistance associated with the difference in magnetoresistance between the vortex ground state and the final C-state configuration. Interestingly, this reversible effect is independent of the incoming RF current amplitude, offering a fast real-time RF threshold detector.

Abnormal neutrophil scattergram obtained using Pentra MS CRP in the patients with myelodysplastic syndrome showing dysgranulopoiesis.

INTRODUCTION: Pentra MS CRP is an automated hematology analyzer capable of cytochemistry using Chlorazol black E, a lipid-staining agent, for white blood cell (WBC) differentials. Pentra MS CRP displays a WBC scattergram according to the cell volume obtained using flow impedance and light absorbance reflecting the Chlorazol black E (CBE)-positive lipid content. METHOD: Neutrophil scattergrams obtained using Pentra MS CRP were compared between 5 patients with myelodysplastic syndrome (MDS) and normal controls. Sudan black B (SBB)-staining patterns of peripheral blood neutrophils were subdivided into four types (types I, II, III, and VI) based on their staining intensity and scored by counting 200 cells. Such SBB scores were also compared between the two groups. RESULTS: Neutrophil scattergrams deviated downward in the MDS group, suggesting the decreased CBE positivity that seemed reflect the reduction of the lipid content in dysplastic neutrophils. SBB scores determined in this study were also decreased in the MDS group when compared with those in normal controls. CONCLUSION: Pentra MS CRP might rapidly generate useful information on dysplastic neutrophils in patients with MDS based on its cytochemistry for WBC differentials during routine laboratory hematology.

Understanding of Phase Noise Squeezing Under Fractional Synchronization of a Nonlinear Spin Transfer Vortex Oscillator.

We investigate experimentally the synchronization of vortex based spin transfer nano-oscillators to an external rf current whose frequency is at multiple integers, as well as at an integer fraction, of the oscillator frequency. Through a theoretical study of the locking mechanism, we highlight the crucial role of both the symmetries of the spin torques and the nonlinear properties of the oscillator in understanding the phase locking mechanism. In the locking regime, we report a phase noise reduction down to -90 dBc/Hz at 1 kHz offset frequency. Our demonstration that the phase noise of these nanoscale nonlinear oscillators can be tuned and eventually lessened, represents a key achievement for targeted radio frequency applications using spin torque devices.

Long-distance propagation of a surface plasmon on the surface of a ferromagnetic metal.

A method for the reduction of the propagation loss of surface plasmons was proposed and experimentally demonstrated. A plasmonic structure, which contains a metal and two dielectric layers of different refractive indexes, is proposed in order to optimize the optical confinement and to reduce the propagation loss of the surface plasmons. Long-distance propagation of a surface plasmon on the surface of a ferromagnetic metal was demonstrated. A low propagation loss of 0.17 dB/µm for a surface plasmon in a Fe/MgO/AlGaAs plasmonic structure was achieved.

Evaluation of the Microsemi CRP, an automated hematology analyzer for rapid 3-part WBC differential and CRP using whole blood.

INTRODUCTION: We evaluated the basic performance of Microsemi CRP, an unique automated hematology analyzer which can simultaneously measure CBC including 3-part WBC differential (3-Diff) and CRP using whole blood treated with EDTA-2K anticoagulant. METHOD: We found that it produced generally the acceptable results for all parameters performed (repeatability, reproducibility, linearity, interference effect, carry over, and correlation) using control materials, fresh human whole bloods, and serum samples. RESULTS: CBC data examined using Microsemi CRP showed the good correlation with the previous model, Micros CRP200 (r ≧ 0.9), and also those obtained using the routine analyzer, ADVIA 2120i (r ≧ 0.989). Concerning the 3-Diff, both GRA (%) and LYM (%) showed the excellent correlation coefficient between Microsemi CRP and Micros CRP200 (r ≧ 0.992) as well as ADVIA 2120i (r ≧ 0.957). MON (%) showed good correlation between Microsemi CRP and Micros CRP200 (r = 0.959), but lower correlation between Microsemi CRP and ADVIA 2120 i (r = 0.471). CRP data showed the good correlation with HITACHI7600 (r ≧ 0.997) and Micros CRP200 (r ≧ 0.997). CONCLUSION: From these findings, we concluded that Microsemi CRP seemed the convenient laboratory analyzer in the setting of point of care testing (POCT) especially at NICU or primary care unit.

Basic evaluation of Pentra MS CRP, a new automated hematology analyzer for rapid 5-part WBC differential and CRP using a small volume of whole blood.

INTRODUCTION: Pentra MS CRP is a new automated hematology analyzer that can rapidly and reliably provide 5-part differential of leukocytes (5-Diff) and C-reactive protein (CRP) within approximately 3.5 min using a small volume of whole blood (35 µL). METHODS: We evaluated the basic performance of Pentra MS CRP and correlations with Sysmex XN-3000, manual microscopic count, and Hitachi LABOSPECT. RESULTS: Pentra MS CRP demonstrated good repeatability and linearity without any significant carryover for all parameters examined (WBC, RBC, HGB, Hct, PLT, 5-Diff, and CRP). Complete blood cell count (CBC) data examined by Pentra MS CRP correlated well with those evaluated by Sysmex XN-3000 (R ≥ 0.9880). Absolute number of NEU, LYM, and EOS also showed the good correlation (R ≥ 0.9866) between the two analyzers. The correlation with the manual microscopic count was within acceptable criteria. Furthermore, when CRP was examined in hemolyzed whole blood by Pentra MS CRP and converted to plasma concentrations according to Hct, it correlated well (R = 0.9964) with serum CRP examined by Hitachi LABOSPECT. CONCLUSION: Pentra MS CRP is a convenient and reliable analyzer especially in the emergency unit of hospitals in which the prompt and simultaneous measurement of CBC including 5-Diff and CRP is often necessary.

Impaired hematopoietic differentiation of RUNX1-mutated induced pluripotent stem cells derived from FPD/AML patients.

Somatic mutation of RUNX1 is implicated in various hematological malignancies, including myelodysplastic syndrome and acute myeloid leukemia (AML), and previous studies using mouse models disclosed its critical roles in hematopoiesis. However, the role of RUNX1 in human hematopoiesis has never been tested in experimental settings. Familial platelet disorder (FPD)/AML is an autosomal dominant disorder caused by germline mutation of RUNX1, marked by thrombocytopenia and propensity to acute leukemia. To investigate the physiological function of RUNX1 in human hematopoiesis and pathophysiology of FPD/AML, we derived induced pluripotent stem cells (iPSCs) from three distinct FPD/AML pedigrees (FPD-iPSCs) and examined their defects in hematopoietic differentiation. By in vitro differentiation assays, FPD-iPSCs were clearly defective in the emergence of hematopoietic progenitors and differentiation of megakaryocytes, and overexpression of wild-type (WT)-RUNX1 reversed most of these phenotypes. We further demonstrated that overexpression of mutant-RUNX1 in WT-iPSCs did not recapitulate the phenotype of FPD-iPSCs, showing that the mutations were of loss-of-function type. Taken together, this study demonstrated that haploinsufficient RUNX1 allele imposed cell-intrinsic defects on hematopoietic differentiation in human experimental settings and revealed differential impacts of RUNX1 dosage on human and murine megakaryopoiesis. FPD-iPSCs will be a useful tool to investigate mutant RUNX1-mediated molecular processes in hematopoiesis and leukemogenesis.

Highly sensitive nanoscale spin-torque diode.

Highly sensitive microwave devices that are operational at room temperature are important for high-speed multiplex telecommunications. Quantum devices such as superconducting bolometers possess high performance but work only at low temperature. On the other hand, semiconductor devices, although enabling high-speed operation at room temperature, have poor signal-to-noise ratios. In this regard, the demonstration of a diode based on spin-torque-induced ferromagnetic resonance between nanomagnets represented a promising development, even though the rectification output was too small for applications (1.4 mV mW(-1)). Here we show that by applying d.c. bias currents to nanomagnets while precisely controlling their magnetization-potential profiles, a much greater radiofrequency detection sensitivity of 12,000 mV mW(-1) is achievable at room temperature, exceeding that of semiconductor diode detectors (3,800 mV mW(-1)). Theoretical analysis reveals essential roles for nonlinear ferromagnetic resonance, which enhances the signal-to-noise ratio even at room temperature as the size of the magnets decreases.

Local and retrograde gene transfer into primate neuronal pathways via adeno-associated virus serotype 8 and 9.

Viral vector-mediated gene transfer has become increasingly valuable for primate brain research, in particular for application of genetic methods (e.g. optogenetics) to study neuronal circuit functions. Neuronal cell tropisms and infection patterns are viable options for obtaining viral vector-mediated transgene delivery that is selective for particular neuronal pathways. For example, several types of viral vectors can infect axon terminals (retrograde infections), which enables targeted transgene delivery to neurons that directly project to a particular viral injection region. Although recent studies in rodents have demonstrated that adeno-associated virus serotype 8 (AAV8) and 9 (AAV9) efficiently transduce neurons, the tropisms and infection patterns remain poorly understood in primate brains. Here, we constructed recombinant AAV8 or AAV9, which expressed an enhanced green fluorescent protein (EGFP) gene driven by a ubiquitous promoter (AAV8-EGFP and AAV9-EGFP, respectively), and stereotaxically injected it into several brain regions in marmosets and macaque monkeys. Immunohistochemical analyses revealed almost exclusive colocalization of EGFP fluorescence via AAV9-mediated gene transfer with a neuron-specific marker, indicating endogenous neuronal tropism of AAV9, which was consistent with our previous results utilizing AAV8. Injections of either AAV8-EGFP or AAV9-EGFP into the marmoset striatum resulted in EGFP expression in local striatal neurons as a result of local infection, as well as expression in dopaminergic neurons of the substantia nigra via retrograde transport along nigrostriatal axonal projections. Retrograde infections were also observed in the frontal cortex and thalamus, which are known to have direct projections to the striatum. These local and retrograde gene transfers were further demonstrated in the geniculocortical pathway of the marmoset visual system. These findings indicate promising capabilities of AAV8 and AAV9 to deliver molecular tools into a range of primate neural systems in pathway-specific manners through their neuronal tropisms and infection patterns.

Large microwave generation from current-driven magnetic vortex oscillators in magnetic tunnel junctions.

Spin-polarized current can excite the magnetization of a ferromagnet through the transfer of spin angular momentum to the local spin system. This pure spin-related transport phenomenon leads to alluring possibilities for the achievement of a nanometer scale, complementary metal oxide semiconductor-compatible, tunable microwave generator that operates at low bias for future wireless communication applications. Microwave emission generated by the persistent motion of magnetic vortices induced by a spin-transfer effect seems to be a unique manner to reach appropriate spectral linewidth. However, in metallic systems, in which such vortex oscillations have been observed, the resulting microwave power is much too small. In this study, we present experimental evidence of spin-transfer-induced vortex precession in MgO-based magnetic tunnel junctions, with an emitted power that is at least one order of magnitude stronger and with similar spectral quality. More importantly and in contrast to other spin-transfer excitations, the thorough comparison between experimental results and analytical predictions provides a clear textbook illustration of the mechanism of spin-transfer-induced vortex precession.

Magnetization-dependent loss in an (Al,Ga)As optical waveguide with an embedded Fe micromagnet.

The dependence of waveguiding loss on the magnetization of a Fe micromagnet embedded into the (Al,Ga)As optical waveguide was examined as a possible readout method for the spin-photon memory. The optical detection of the magnetization direction of a Fe micromagnet was demonstrated for the micromagnet sizes of 3 microm x 4 microm and 3 microm x 8 microm with signal-to-noise ratios of 4.8 and 6 dB, respectively. In the case of smaller sizes, the use of spin injection from the micromagnet into a semiconductor optical amplifier was proposed for the optical detection of the magnetization.