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625 results on '"Hayakawa, J."'

1. Temperature and thickness dependence of tunneling anisotropic magnetoresistance in exchange-biased Py/IrMn/MgO/Ta stacks

Author

Reichlova, H., Novak, V., Kurosaki, Y., Yamada, M., Yamamoto, H., Nishide, A., Hayakawa, J., Takahashi, H., Marysko, M., Wunderlich, J., Marti, X., and Jungwirth, T.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We investigate the thickness and temperature dependence of a series of Ni0:8Fe0:2/Ir0:2Mn0:8 bilayer samples with varying thickness ratio of the ferromagnet/antiferromagnet (tFM/tAFM) in order to explore the exchange coupling strengths in tunneling anisotropic magnetoresistance (TAMR) devices. Specific values of tFM/tAFM lead to four distinct scenarios with specific electric responses to moderate magnetic fields. The characteristic dependence of the measured TAMR signal on applied voltage allows us to confirm its persistence up to room temperature despite an overlapped contribution by a thermal magnetic noise.

Published
2016
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2. Storing magnetic information in IrMn/MgO/Ta tunnel junctions via field-cooling

Author

Petti, D., Albisetti, E., Reichlová, H., Gazquez, J., Varela, M., Molina-Ruiz, M., Lopeandía, A. F., Olejník, K., Novák, V., Fina, I., Dkhil, B., Hayakawa, J., Marti, X., Wunderlich, J., Jungwirth, T., and Bertacco, R.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Abstract

Tunneling junctions containing no ferromagnetic elements have been fabricated and we show that distinct resistance states can be set by field cooling the devices from above the N\'eel along different orientations. Variations of the resistance up to 10% are found upon field cooling in applied fields of 2T, in-plane or out of plane. Below TN, we found that the metastable states are insensitive to magnetic fields thus constituting a memory element robust against external magnetic fields. Our work provides the demonstration of an electrically readable magnetic memory device, which contains no ferromagnetic elements and stores the information in an antiferromagnetic active layer.

Published
2013
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4. Electrical measurement of antiferromagnetic moments in exchange-coupled IrMn/NiFe stacks

Author

Marti, X., Park, B. G., Wunderlich, J., Reichlova, H., Kurosaki, Y., Yamada, M., Yamamoto, H., Nishide, A., Hayakawa, J., Takahashi, H., and Jungwirth, T.

Subjects
Condensed Matter - Materials Science
Abstract

We employ the recently discovered antiferromagnetic tunneling anisotropic magnetoresistance to study the behavior of antiferromagnetically ordered moments in IrMn exchange coupled to NiFe. Experiments performed by common laboratory tools for magnetization and electrical transport measurements allow us to directly link the broadening of the NiFe hysteresis loop and its shift (exchange bias) to the rotation and pinning of antiferromagnetic moments in IrMn. At higher temperatures, the broadened loops show zero shift which correlates with the observation of fully rotating antiferromagnetic moments inside the IrMn film. The onset of exchange bias at lower temperatures is linked to a partial rotation between distinct metastable states and pinning of the IrMn antiferromagnetic moments in these states. The observation complements common pictures of exchange bias and reveals the presence of an electrically measurable memory effect in an antiferromagnet., Comment: 4 pages, 5 figures

Published
2011
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5. Tunneling anisotropic magnetoresistance of NiFe/IrMn/MgO/Pt stack: An antiferromagnet based spin-valve

Author

Park, B. G., Wunderlich, J., Marti, X., Holy, V., Kurosaki, Y., Yamada, M., Yamamoto, H., Nishide, A., Hayakawa, J., Takahashi, H., Shick, A. B., and Jungwirth, T.

Subjects
Condensed Matter - Materials Science
Abstract

Spin-valve is a microelectronic device in which high and low resistance states are realized by utilizing both charge and spin of carriers. Spin-valve structures used in modern hard drive read-heads and magnetic random access memories comprise two ferromagnetic (FM) electrodes whose relative magnetization orientations can be switched between parallel and antiparallel configurations, yielding the desired giant or tunneling magnetoresistance effect. In this paper we demonstrate >100$% spin-valve-like signal in a NiFe/IrMn/MgO/Pt stack with an antiferromagnet (AFM) on one side and a non-magnetic metal on the other side of the tunnel barrier. FM moments in NiFe are reversed by external fields <50mT and the exchange-spring effect of NiFe on IrMn induces rotation of AFM moments in IrMn which is detected by the measured tunneling anisotropic magnetoresistance (TAMR). Our work demonstrates a spintronic element whose transport characteristics are governed by an AFM. It demonstrates that sensitivity to low magnetic fields can be combined with large, spin-orbit coupling induced magneto-transport anisotropy using a single magnetic electrode. The AFM-TAMR provides means to study magnetic characteristics of AFM films by an electronic transport measurement., Comment: 8 pages, 4 figures

Published
2010

6. MgO barrier-perpendicular magnetic tunnel junctions with CoFe/Pd multilayers and ferromagnetic insertion layers

Author

Mizunuma, K., Ikeda, S., Park, J. H., Yamamoto, H., Gan, H., Miura, K., Hasegawa, H., Hayakawa, J., Matsukura, F., and Ohno, H.

Subjects
Condensed Matter - Materials Science
Abstract

The authors studied an effect of ferromagnetic (Co20Fe60B20 or Fe) layer insertion on tunnel magnetoresistance (TMR) properties of MgO-barrier magnetic tunnel junctions (MTJs) with CoFe/Pd multilayer electrodes. TMR ratio in MTJs with CoFeB/MgO/Fe stack reached 67% at an-nealing temperature (Ta) of 200 degree C and then decreased rapidly at Ta over 250 degree C. The degradation of the TMR ratio may be related to crystallization of CoFe(B) into fcc(111) or bcc(011) texture result-ing from diffusion of B into Pd layers. MTJs which were in-situ annealed at 350oC just after depo-siting bottom CoFe/Pd multilayer showed TMR ratio of 78% by post annealing at Ta =200 degree C., Comment: 12 pages, 4 figures

Published
2009
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11. Persistence of recipient-derived as well as donor-derived clones of cytomegalovirus pp65-specific cytotoxic T cells long after allogeneic hematopoietic stem cell transplantation

Author

Terasako-Saito, K., Nakasone, H., Tanaka, Y., Yamazaki, R., Sato, M., Sakamoto, K., Ishihara, Y., Kawamura, K., Akahoshi, Y., Hayakawa, J., Wada, H., Harada, N., Nakano, H., Kameda, K., Ugai, T., Yamasaki, R., Ashizawa, M., Kimura, S.-I., Kikuchi, M., Tanihara, A., Kanda, J., Kako, S., Nishida, J., and Kanda, Y.

Published
2014
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17. Half-metallic [Fe.sub.3][O.sub.4] films for high-sensitivity magnetoresistive devices

Author

Takahashi, H., Soeya, S., Hayakawa, J., Ito, K., Kida, A., Asano, H., and Matsui, M.

Subjects
Electromagnetism -- Research, Thin films -- Research, Dielectric films -- Research, Business, Electronics, Electronics and electrical industries
Abstract

By RF sputtering on a MgO (100) substrate, we have made [Fe.sub.3][O.sub.4] (111) metal and [Fe.sub.3][O.sub.4] (001)/TiN (001) films that have Verwey temperature ([T.sub.V]) near 120 K. The saturation magnetizations and resistivities of those [Fe.sub.3][O.sub.4] films were comparable to those of bulk [Fe.sub.3] [O.sub.4], and the magnetoresistive (MR) ratio and MR ratio area product A[DELTA]R measured for various materials structures of current perpendicular to plane (CPP) samples using [Fe.sub.3][O.sub.4] (111) increased sharply at 120 K. This increase around [T.sub.V] seemed to be related to the change in the [Fe.sub.3][O.sub.4] crystal. The A[DELTA]R and MR of CPP-GMR samples using [Fe.sub.3][O.sub.4] (001), on the other hand, such as [Ni.sub.80][Fe.sub.20]/TiN/[Fe.sub.3][O.sub.4] (001)TiN (001/, [Co.sub.75][Fe.sub.25]TiN/[Fe.sub.3][O.sub.4] (001)/TiN (001), and [Fe.sub.3][O.sub.4]/TiN/[Fe.sub.3][O.sub.4] (001)/TiN (001), were 2-4 times larger than those of CPP-GMR samples using [Fe.sub.3] [O.sub.4] (111) were. And for [Fe.sub.3][O.sub.4] (001) the increase of MR at [T.sub.V] was smaller than it was for [Fe.sub.3][O.sub.4] (111). Index Terms--Current perpendicular to plane, [Fe.sub.3][O.sub.4], magnetoresistive effect, TiN, Verway temperature.

Published
2004

20. Electronic structure of polycrystalline AMoO3

Author

Mizoguchi, H., Fukumi, K., Kitamura, N., Takeuchi, T., Hayakawa, J., Yamanaka, H., Yanagi, H., Hosono, H., and Kawazoe, H.

Subjects
Polycrystalline semiconductors -- Research, Electronic structure -- Research, Physics
Abstract

Research was conducted to examine the possibility of application of transition metal oxides to transparent conductors. Electronic and optical spectroscopies were used to estimate the electronic structure of AMoO3 with perovskite structure. Results provide evidence of the possibility of application in transparent conductors for the ultraviolet region since no intense peaks were detected in the energy region between the two absorption bands.

Published
1999

22. Cream fur: a new mouse mutation that may cause unusual lipid metabolism

Author

Hayakawa, J., Nikaido, H., Ohkawa, T., and Kitoh, J.

Subjects
Mice -- Genetic aspects, Lipid metabolism -- Research, Biological sciences
Abstract

A cream yellow coat color had been found in a breeding colony of albino mouse of strain CAL20. Genetic studies showed that the cream yellow coat color phenotype was regulated by a single recessive mutant gene on chromosome 13. The cream yellow hair was also found to have more fatty acid than normal hair and that the color was due to an unusual lipid metabolism. The locus was named cream fur locus and was given the symbol crf. It was also observed that recombination frequencies near the area of the crf locus were very different between male and female meiosis.

Published
1998

33. The origin of bias-voltage dependence in CoFe/SrTiO3/La0.7Sr0.3MnO3 magnetic tunnel junctions

Author

Hayakawa, J., Ito, K., Kokado, S., Ichimura, M., Sakuma, A., Sugiyama, M., Asano, H., and Matsui, M.

Subjects
Strontium -- Magnetic properties, Lanthanum -- Magnetic properties, Cobalt -- Magnetic properties, Physics
Abstract

Single crystalline La0.7Sr.0.3MnO3 (LSMO) electrode and SrTiO3 (STO) barrier were used for examining the relationship between the oxidized state in the barrier and the bias-voltage dependence on tunnel magnetoresistance (TMR) effect in Co90Fe10/SrTiO3(STO)/La0.7Sr0.3MnO3(LSMO) magnetic tunnel junctions. An asymmetric dependence with regard to the bias direction was observed in the TMR junction with stoichiometrically fabricated STO barrier while the TMR symmetrically declined in case of an oxygen deficiency of the STO barrier.

Published
2002

34. Preparation of optical materials used in non-visible region (M-17)

Author

Hayakawa, J

Subjects
Materials Processing
Abstract

The purpose of the experiment was the following: development of containerless glass melting technique; fabrication of high purity glass; and development of acoustic levitation technique. For the space experiment, glass 65CaO-25Ga2O3-10GeO2 was selected out of various types of glasses. The expected results are: ultra-high purity glass and manipulation by acoustics.

Published
1993

37. Direct measurement of current-induced fieldlike torque in magnetic tunnel junctions.

Author

Devolder, T., Kim, Joo-Von, Chappert, C., Hayakawa, J., Ito, K., Takahashi, H., Ikeda, S., and Ohno, H.

Subjects
TORQUE, ANISOTROPY, MAGNETIZATION, NANOSTRUCTURES, EXTRACTION (Chemistry), HEATING
Abstract

We present a direct and quantitative method to measure the current-induced fieldlike torques in current perpendicular to plane magnetic multilayers. We illustrate this method on nanopillars patterned from MgO-based magnetic tunnel junctions. By measuring how the Stoner astroids are displaced, shrinked, and distorted under the influence of a bias current, we separate the contributions of the current-induced fieldlike torque, the current-induced heating, and the current-induced spin torque. In contrast to high frequency based measurement methods that are better suited to analyze the spin torque than the fieldlike term, our measurement is direct and quantitative for the current-induced fieldlike term and the heating induced reduction in shape anisotropy, while only qualitative for the spin torque. [ABSTRACT FROM AUTHOR]

Published
2009
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38. Electrical time-domain observation of magnetization switching induced by spin transfer in magnetic nanostructures (invited).

Author

Devolder, T., Hayakawa, J., Ito, K., Takahashi, H., Ikeda, S., Katine, J. A., Carey, M. J., Crozat, P., Kim, J. V., Chappert, C., and Ohno, H.

Abstract

We have measured the distribution of switching times in spin-transfer switching induced by fast current pulses in two pillar-shaped systems: (i) spin valves and (ii) MgO-based magnetic tunnel junctions. (i) Spin valves can sustain high currents, such that the application of pulsed currents of amplitude a few times that of the static switching threshold is possible. This makes subnanosecond switching within reach. In that limit, the pulse durations leading to switching follow a multiply stepped distribution at 300 K and a regular distribution at 40 K. At 300 K, this reflects the precessional nature of the switching, which proceeds through a small number of precession cycles. The switching time distribution can be modeled from the thermal variance of the initial magnetization orientations. At 40 K, nonuniform magnetization switching occurs. (ii) In MgO-based tunnel junctions, we could follow individual time-resolved switching events with a 13 GHz bandwidth. The switching proceeds through a nanosecond-scale random incubation delay during which the resistance is quiet, followed by a sudden (400 ps duration) transition terminated by a pronounced ringing that is damped within 1.5 ns. While the incubation delay is probabilistic, the following time dependence of the resistance is reproducible. [ABSTRACT FROM AUTHOR]

Published
2008
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41. Temperature and thickness dependence of tunneling anisotropic magnetoresistance in exchange-biased Py/IrMn/MgO/Ta stacks

Author

Kurosaki, Y., Yamada, M., Yamamoto, H., Nishide, A., Hayakawa, J., Takahashi, H., Marysko, M., Wunderlich, J., Marti, X., and Jungwirth, T.

Abstract

Weinvestigate the thickness and temperature dependence of a series of Ni0.8Fe0.2/Ir0.2Mn0.8 bilayer samples with varying thickness ratio of the ferromagnet/antiferromagnet (tFM tAFM) in order to explore the exchange coupling strengths in tunneling anisotropic magnetoresistance (TAMR) devices. Specific values of tFM tAFM lead to four distinct scenarios with specific electric responses to moderate magnetic fields. The characteristic dependence of the measured TAMR signal on applied voltage allows us to confirm its persistence up to room temperature despite an overlapped contribution by a thermal magnetic noise.

Published
2016

42. Tunnel magnetoresistance in MgO-barrier magnetic tunnel junctions with bcc-CoFe(B) and fcc-CoFe free layers

Author

Ikeda, S., Hayakawa, J., Tanikawa, T., Lee,Y.M., and Ohno, H.

Subjects
Magnetoresistance -- Analysis, Magnesium oxide -- Magnetic properties, Tunneling (Physics) -- Analysis, Physics
Abstract

The spin tunneling transport in magnetic tunnel junctions (MTJs) with C[o.sub.40]F[e.sub.40][B.sub.20], and C[o.sub.90]F[e.sub.10] free layers which are deposited on the lower electrode consisting of the same C[o.sub40]F[e.sub40][B.sub.20] reference layer/MgO barrier are investigated. It is revealed that no high tunnel magnetoresistance ratio is observed for the MTJs with C[o.sub.90]F[e.sub.10] free layer having a polycrystalline fcc structure.

Published
2006

45. Current-driven switching of exchange biased spin-valve giant magnetoresistive nanopillars using a conducting nanoprobe

Author

Ito, K., Hayakawa, J, Hashizume, T., Heike, S, Fujimore, M, Steen, J., Brugger, J., and Ohno, H.

Subjects
Atomic force microscopy -- Research, Copper -- Magnetic properties, Copper -- Electric properties, Cobalt -- Magnetic properties, Cobalt -- Electric properties, Manganese -- Magnetic properties, Manganese -- Electric properties, Magnetoresistance -- Research, Physics
Abstract

An array of exchange biased spin-valve giant-magnetoresistance nanopillars is fabricated and the current I dependence of the resistance R is investigated using an electrically conducting atomic-force microscope (AFM) probe contact at room temperature. The findings show a current inducted switching in MnIr/CoFe/Cu/CoFe/NiFe nanopillar using the AFM probe contact.

Published
2004

46. Fabrication and magnetoresistive effect of current perpendicular to plane devices using half-metallic Fe3O4 thin films on metallic films

Author

Takahashi, H., Soeya, S., Hayakawa, J., Ito, K., Kida, A., Yamamoto, C., Asano, H., and Matsui, M.

Subjects
Dielectric films -- Research, Thin films -- Research, Iron oxides -- Magnetic properties, Magnetoresistance -- Research, Physics
Abstract

The current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) devices having half-metallic Fe3O4 for their magnetic layers are determined along with the fabrication of Fe3O4 films on Au layers at low temperature. It was seen that the magnetoresistance (MR) ratio of Fe3O4/Au/Fe3O4 on the Au underlayer was four times larger than that of the NiFe-type CPP-GMR for the same Fe3O4 bottom layer thickness.

Published
2003

49. Magnetotransport in perovskite series La_{n-nx}Ca_{1＋nx}Mn_nO_{3n＋1} ferromagnets

Author

Asano, H., Hayakawa, J., and Matsui, M.

Abstract

The perovskite series La_{n-nx}Ca_{1＋nx}Mn_nO_{3n＋1｝(n=2,3,and ∞)composed of n layers of MnO2 is a colossal magnetoresistance (CMR) ferromagnet. Results on the transport properties of epitaxial a-axis thin-film samples with a fixed carrier concentration (x=0.3) have indicated that a reduction in the number of layers results in systematic changes in the various features. These include an increase in resistivity, a decrease in the resistivity peak temperature Tρc corresponding to the metal-insulator transition, an enhancement of the maximum MR near Tρc, and an increase in the low-temperature intrinsic MR. In order to explain the variation in these features with the number of MnO2 layers, it is necessary to take both c-axis transfer interaction and two-dimensional spin fluctuation into account.

Published
1998

50. Two-dimensional ferromagnetic ordering and magnetoresistance in the layered perovskite La_{2-2x}Ca_｛1＋2x｝Mn_2O_7

Author

Asano, H., Hayakawa, J., and Matsui, M.

Subjects
Condensed Matter::Materials Science, Condensed Matter::Superconductivity, Condensed Matter::Strongly Correlated Electrons
Abstract

The resistivity and magnetization of layered perovskite La_{2-2x}Ca_{1＋2x}Mn_2O_7 have been studied systematically using bulk samples with a wide doping concentration range 0≼x≼0.5 and epitaxial thin film samples with x=0.3. The system becomes a metallic ferromagnet for doping concentrations 0.22≼x≼0.5. In this doping region, results for bulk samples as well as for thin films have clearly shown that there are two types of ferromagnetic ordering, possibly originating from an anisotropic exchange interaction. Magnetoresistance is observed over a wide temperature range below the ferromagnetic ordering temperatures. Based on these results, a model of temperature-dependent spin ordering is presented for a double perovskite ferromagnet, which suggests that there is a two-dimensional ferromagnetic alignment at temperatures between the two ordering temperatures.

Published
1997

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