Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Yuichiro Kurokawa Last modified date:2019.06.27

Assistant Professor / Department of Electronics / Faculty of Information Science and Electrical Engineering


Papers
1. Yuichiro Kurokawa, Masakazu Wakae, Satoshi Sumi, Hiroyuki Awano, Kohei Ohnishi, Hiromi Yuasa, Spin-orbit torque-driven current-induced domain wall motion in Gd-Fe magnetic wires, Japanese Journal of Applied Physics, 10.7567/1347-4065/aafa91, 58, 3, 2019.03, We fabricated Gd-Fe/Ta/sub. and W/Gd-Fe/Ta/sub. perpendicular magnetized magnetic wires and investigated current-induced domain wall motion (CIDWM) in them. The propagation field of the Gd-Fe wires is low (∼3 mT), and the wires were found to have a low threshold current density (∼3.1 ×1010 A m-2) of CIDWM. The directions of the CIDWM in Gd-Fe/Ta and W/Gd-Fe/Ta wires are opposite to each other, indicating that the CIDWM in both wires is driven by spin-orbit torque because the spin Hall torque generated by the Ta underlayer and W cap layer oppose each other..
2. Fumiya Nakata, Takumi Niimura, Yuichiro Kurokawa, Hiromi Yuasa, Spin Seebeck voltage enhancement by Mn system metals insertion at the interface between YIG and nonmagnetic layer, Japanese Journal of Applied Physics, 10.7567/1347-4065/aafb5c, 58, 2019.01, The spin Seebeck voltage was successfully increased by IrMn or Mn insertion into the interface Y3Fe5O12 and nonmagnetic Pt and TaW with positive and negative spin Hall angle, respectively. The magnitude of the spin Seebeck coefficient |S| of the samples with IrMn and Mn were higher than that with Ru insertion, which indicates that the existence of the magnetic moment is important for the spin Seebeck coefficient. Furthermore, |S| of the samples with IrMn and Mn were higher than oxide antiferromagnetic NiO, which suggests the metallic layer insertion is effective for enlarging |S| owing to the relatively long spin diffusion length. Since the inserted IrMn and NiO take the paramagnetic states as well as Mn, it is supposed that the spin fluctuation in the paramagnetic insertion layers play an important role in enhancing the spin current..
3. Masakazu Wakae, Yuichiro Kurokawa, Hiromi Yuasa, Observation of spin-orbit torque-induced magnetization switching in Gd-Fe perpendicular magnetized wire with in-plane exchange bias field, Japanese Journal of Applied Physics, 10.7567/1347-4065/aaf877, 58, 2019.01, We fabricated a Ta/Gd-Fe/Ta and a Ta/Gd-Fe/Ir22Mn78/Co90Fe10/Ta multilayered magnetic wire and investigated spin-orbit torque current-induced magnetization switching in these wires. Magnetization switching in the Ta/Gd-Fe/Ir22Mn78/Co90Fe10/Ta multilayered magnetic wire can be observed by an electric current even if the external in-plane magnetic field is not applied at all. Moreover, we successfully observed the periodical magnetization switching in the Ta/Gd-Fe/Ir22Mn78/Co90Fe10/Ta multilayered magnetic wire in zero magnetic field. This indicates that the present wire is a promising material to realize magnetic random access memory with low power consumption..
4. Keisuke Yamada, Yuichiro Kurokawa, Kazuma Kogiso, Hiromi Yuasa, Mutsuhiro Shima, Observation of longitudinal spin seebeck voltage in YIG films chemically prepared by co-precipitation and spin coating, IEEE Transactions on Magnetics, 10.1109/TMAG.2018.2865199, 55, 2, 2019.02, Longitudinal spin Seebeck effect (LSSE) of Y3Fe5O12 (YIG) thin films chemically prepared on a Si substrate with a SiO2 surface layer has been investigated with a particular focus on its dependence on the metal (Pt or W) for the capping layer used to carry out the measurements. The YIG films are prepared by a combination of co-precipitation, spin coating, and annealing processes. The structural characterization by X-ray diffraction proves that the films are polycrystalline in a garnet phase with an average crystallite size of 34 nm. The microstructural analyses of the film surface by scanning electron microscopy and scanning probe microscopy show that the roughness Ra of the film is 31 nm. The magnetic easy axis of the YIG films is in the direction parallel to the films. We have found that the polarity of the LSSE voltage VLSSE measured with a Pt capping layer apparently differs from that observed when a W capping layer is used. The value of VLSSE increases almost linearly with increasing temperature difference Δ T independent of the choice of metal for the capping layer. The observed LSSE for the polycrystalline YIG films is one order of magnitude smaller than that reported for YIG and Bi:YIG single-crystal samples grown by metal-organic decomposition..
5. Yuichiro Kurokawa, Hiroyuki Awano, Multilayered current-induced domain wall motion in Pt/Tb-Co/Ta/Tb-Co/Pt magnetic wire, AIP ADVANCES, 10.1063/1.5017814, 8, 2, 2018.02, We fabricated a Pt (3 nm)/Tb0.28Co0.72 (4 nm)/Ta (4 nm)/Tb0.26Co0.74 (4 nm)/Pt
(3 nm) multilayered magnetic wire and investigated current-induced domain wall
motion within it.We found that the Hall resistance of the Pt/Tb-Co/Ta/Tb-Co/Pt wire
has four stable levels under a magnetic field of zero. Moreover, we observed that the
domain walls in both the upper and lower ferromagnetic layers are controlled by a
single current source. This indicates that Pt/Tb-Co/Ta/Tb-Co/Pt wire can be used in
multi-level magnetic wire memory..
6. Hiromi Yuasa, Fumiya Nakata, Ryohei Nakamura, Yuichiro Kurokawa, Spin Seebeck coefficient enhancement by using Ta50W50 alloy and YIG/Ru interface, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 10.1088/1361-6463/aaaf89, 51, 13, 2018.04.
7. Yuichiro Kurokawa, Akihiro Shibata, Hiroyuki Awano, Enhancement of spin orbit torques in a Tb-Co alloy magnetic wire by controlling its Tb composition, AIP ADVANCES, 10.1063/1.4974280, 7, 5, 2017.05.
8. Yuichiro Kurokawa, Do Bang, Hiroyuki Awano, Thermally Assisted Current-Induced Domain Wall Motion in Tb/Co Magnetic Multilayered Wire with a High Domain Wall Propagation Field, IEEE Transactions on Magnetics, 10.1109/TMAG.2017.2676086, 53, 7, 2017.07, We investigated the current-induced domain wall (DW) motion in Tb/Co multilayered wire with various substrate temperatures (Ts). The coercivity and DW propagation field of the Tb/Co multilayered film are 10 and 8 kOe, respectively. In the Tb/Co wire, the DW velocity is 2.4 m/s for a current density of 4.5 × 1011 Am2 at room temperature. At Ts = 343 K, we also found that the DW velocity is about two times higher than that at room temperature. The enhancement of DW velocity can be attributed to thermally activated creep DW motion and/or the reduction of the depinning current density..
9. Yuichiro Kurokawa, Ryogo Yoshimura, Satoshi Sumi, Hiroyuki Awano, Thermal reduction of the threshold current density for current-induced domain wall motion in Tb-Co magnetic alloy wire, AIP ADVANCES, 10.1063/1.4979727, 7, 3, 2017.03.
10. Yuichiro Kurokawa, Masaya Kawamoto, Hiroyuki Awano, Current-induced domain wall motion attributed to spin Hall effect and Dzyaloshinsky-Moriya interaction in Pt/GdFeCo (100 nm) magnetic wire, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.7567/JJAP.55.07MC02, 55, 7, 2016.07.