Change search
Link to record
Permanent link

Direct link
BETA
Chung, Sunjae
Publications (10 of 14) Show all publications
Mazraati, H., Etesami, S. R., Banuazizi, S. A., Chung, S., Houshang, A., Awad, A. A., . . . Åkerman, J. (2018). Auto-oscillating Spin-Wave Modes of Constriction-Based Spin Hall Nano-oscillators in Weak In-Plane Fields. Physical Review Applied, 10(5), Article ID 054017.
Open this publication in new window or tab >>Auto-oscillating Spin-Wave Modes of Constriction-Based Spin Hall Nano-oscillators in Weak In-Plane Fields
Show others...
2018 (English)In: Physical Review Applied, E-ISSN 2331-7019, Vol. 10, no 5, article id 054017Article in journal (Refereed) Published
Abstract [en]

We experimentally study the auto-oscillating spin-wave modes in Ni(80)Fc(20)/beta-W constriction-based spin Hall nano-oscillators as a function of bias current, strength of the in-plane applied field, and azimuthal field angle in the low-field range of 40-80 mT. We observe two different spin-wave modes: (i) a linearlike mode confined to the internal field minima near the edges of the nanoconstriction, and only weakly dependent on the bias current and the applied-field angle, and (ii) a second, lower-frequency mode with significantly higher threshold current and stronger dependence on both the bias current and the externalfield angle. Micromagnetic modeling qualitatively reproduces the experimental data and reveals that the second mode is a spin-wave bullet and that the spin Hall nano-oscillator mode hops between the two modes, resulting in a substantial increase in linewidths. In contrast to the linearlike mode, the bullet is localized in the middle of the constriction and shrinks with increasing bias current. Using intrinsic frequency doubling at zero field angle, we can reach frequencies above 9 GHz in fields as low as 40 mT, which is important for the development of low-field spintronic oscillators with applications in microwave-signal generation and neuromorphic computing.

Place, publisher, year, edition, pages
American Physical Society, 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-239478 (URN)10.1103/PhysRevApplied.10.054017 (DOI)000449412100003 ()2-s2.0-85056389030 (Scopus ID)
Funder
EU, Horizon 2020, 687676
Note

QC 20181126

Available from: 2018-11-26 Created: 2018-11-26 Last updated: 2018-11-26Bibliographically approved
Jiang, S., Etesami, S. R., Chung, S., Le, Q. T., Houshang, A. & Åkerman, J. (2018). Impact of the Oersted Field on Droplet Nucleation Boundaries. IEEE Magnetics Letters, 9, Article ID 3104304.
Open this publication in new window or tab >>Impact of the Oersted Field on Droplet Nucleation Boundaries
Show others...
2018 (English)In: IEEE Magnetics Letters, ISSN 1949-307X, E-ISSN 1949-3088, Vol. 9, article id 3104304Article in journal (Refereed) Published
Abstract [en]

We investigate how the Oersted field affects the magnetic droplet nucleation boundary in spin-torque nano-oscillators based on orthogonal spin-valve stacks with a perpendicular magnetic anisotropy Co/Ni free layer and an easy-plane anisotropy Ni80Fe20 fixed layer. The current-field nucleation boundary is determined experimentally using both microwave signal and dc resistance measurements. The Oersted field can, in principle, have an impact on droplet nucleation. This effect is considered approximately using an analytical equation for the nucleation boundary, which is extended to cover fields larger than the fixed-layer saturation field. We test the accuracy of this approach by comparing with micromagnetic simulations. Finally, we carry out a numerical fit to experimental data and find good agreement.

Place, publisher, year, edition, pages
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2018
Keywords
Spin electronics, magnetic droplet, Oersted field, spin-torque nano-oscillators
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-232425 (URN)10.1109/LMAG.2018.2850007 (DOI)000438127100001 ()2-s2.0-85049058526 (Scopus ID)
Funder
Swedish Foundation for Strategic Research Swedish Research CouncilKnut and Alice Wallenberg FoundationEU, FP7, Seventh Framework Programme, 307144
Note

QC 20180725

Available from: 2018-07-25 Created: 2018-07-25 Last updated: 2018-09-11Bibliographically approved
Mohseni, S. M., Hamdi, M., Yazdi, H. F., Banuazizi, S. A., Redjai Sani, S., Chung, S., . . . Mohseni, S. M. (2018). Magnetic droplet soliton nucleation in oblique fields. Physical Review B Condensed Matter, 97(184402)
Open this publication in new window or tab >>Magnetic droplet soliton nucleation in oblique fields
Show others...
2018 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 97, no 184402Article in journal (Refereed) Published
Abstract [en]

We study the auto-oscillating magnetodynamics in orthogonal spin-torque nano-oscillators (STNOs) as a function of the out-of-plane (OOP) magnetic-field angle. In perpendicular fields and at OOP field angles down to approximately 50°, we observe the nucleation of a droplet. However, for field angles below 50°, experiments indicate that the droplet gives way to propagating spin waves, in agreement with our micromagnetic simulations. Theoretical calculations show that the physical mechanism behind these observations is the sign changing of spin-wave nonlinearity (SWN) by angle. In addition, we show that the presence of a strong perpendicular magnetic anisotropy free layer in the system reverses the angular dependence of the SWN and dynamics in STNOs with respect to the known behavior determined for the in-plane magnetic anisotropy free layer. Our results are of fundamental interest in understanding the rich dynamics of nanoscale solitons and spin-wave dynamics in STNOs.

Place, publisher, year, edition, pages
American Physical Society, 2018
Keywords
nanocontact, spin torque nano-oscillator, droplet, nucleation
National Category
Nano Technology Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-228245 (URN)10.1103/PhysRevB.97.184402 (DOI)000431986600004 ()2-s2.0-85047128171 (Scopus ID)
Note

QC 20180524

Available from: 2018-05-21 Created: 2018-05-21 Last updated: 2018-06-05Bibliographically approved
Sheykhifard, Z., Mohseni, S. M., Tork, B., Hajiali, M. R., Jamilpanah, L., Rahmati, B., . . . Roozmeh, S. E. (2018). Magnetic graphene/Ni-nano-crystal hybrid for small field magnetoresistive effect synthesized via electrochemical exfoliation/deposition technique. Journal of materials science. Materials in electronics, 29(5), 4171-4178
Open this publication in new window or tab >>Magnetic graphene/Ni-nano-crystal hybrid for small field magnetoresistive effect synthesized via electrochemical exfoliation/deposition technique
Show others...
2018 (English)In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 29, no 5, p. 4171-4178Article in journal (Refereed) Published
Abstract [en]

Two-dimensional heterostructures of graphene (Gr) and metal/semiconducting elements convey new direction in electronic devices. They can be useful for spintronics because of small spin orbit interaction of Gr as a non-magnetic metal host with promising electrochemical stability. In this paper, we demonstrate one-step fabrication of magnetic Ni-particles entrapped within Gr-flakes based on simultaneous electrochemical exfoliation/deposition procedure by two-electrode system using platinum as the cathode electrode and a graphite foil as the anode electrode. The final product is an air stable hybrid element including Gr flakes hosting magnetic Ni-nano-crystals showing superparamagnetic-like response and room temperature giant magnetoresistance (GMR) effect at small magnetic field range. The GMR effect is originated from spin scattering through ferromagnetic/non-magnetic nature of Ni/Gr heterostructure and interpreted based on a phenomenological spin transport model. Our work benefits from XRD, XPS, Raman, TEM, FTIR and VSM measurements We addressed that how our results can be used for rapid manufacturing of magnetic Gr for low field magneto resistive elements and potential printed spintronic devices.

Place, publisher, year, edition, pages
Springer, 2018
Keywords
Doped Topological Insulator, Spin-Orbit Torque, Conductive Electrodes, Exfoliated Graphene, Nanoparticles, Spintronics, Nickel, Films, Composites, Absorption
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-223250 (URN)10.1007/s10854-017-8362-8 (DOI)000424338500076 ()2-s2.0-85037378773 (Scopus ID)
Note

QC 20180220

Available from: 2018-02-20 Created: 2018-02-20 Last updated: 2018-02-20Bibliographically approved
Jiang, S., Chung, S., Diez, L. H., Le, Q. T., Magnusson, F., Ravelosona, D. & Åkerman, J. (2018). Tuning the magnetodynamic properties of all-perpendicular spin valves using He+ irradiation. AIP Advances, 8(6), Article ID 065309.
Open this publication in new window or tab >>Tuning the magnetodynamic properties of all-perpendicular spin valves using He+ irradiation
Show others...
2018 (English)In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 8, no 6, article id 065309Article in journal (Refereed) Published
Abstract [en]

Using He+ ion irradiation, we demonstrate how the magnetodynamic properties of both ferromagnetic layers in all-perpendicular [Co/Pd]/Cu/[Co/Ni] spin valves can be tuned by varying the He+ ion fluence. As the perpendicular magnetic anisotropy of both layers is gradually reduced by the irradiation, different magnetic configurations can be achieved from all-perpendicular (up arrow up arrow), through orthogonal (->up arrow), to all in-plane (paired right arrows). In addition, both the magnetic damping (alpha) and the inhomogeneous broadening (Delta H-0) of the Co/Ni layer improve substantially with increasing fluence. While the GMR of the spin valve is negatively affected, decreasing linearly from an original value of 1.14% to 0.4% at the maximum fluence of 50x10(14) He+/cm(2), most of the Co/Ni layer improvement is achieved already at a fluence of 10x10(14) He+/cm(2), for which GMR only reduces to 0.9%.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-232262 (URN)10.1063/1.5024472 (DOI)000436855300082 ()2-s2.0-85048621398 (Scopus ID)
Funder
Swedish Foundation for Strategic Research Swedish Research CouncilKnut and Alice Wallenberg FoundationEU, FP7, Seventh Framework Programme, 307144
Note

QC 20180719

Available from: 2018-07-19 Created: 2018-07-19 Last updated: 2018-09-11Bibliographically approved
Jiang, S., Chung, S., Le, Q. T., Mazraati, H., Houshang, A. & Åkerman, J. (2018). Using Magnetic Droplet Nucleation to Determine the Spin Torque Efficiency and Asymmetry in Co-x(Ni,Fe)(1-x) Thin Films. Physical Review Applied, 10(5), Article ID 054014.
Open this publication in new window or tab >>Using Magnetic Droplet Nucleation to Determine the Spin Torque Efficiency and Asymmetry in Co-x(Ni,Fe)(1-x) Thin Films
Show others...
2018 (English)In: Physical Review Applied, E-ISSN 2331-7019, Vol. 10, no 5, article id 054014Article in journal (Refereed) Published
Abstract [en]

We demonstrate how to extract the material-dependent spin-torque efficiency (epsilon) and asymmetry (lambda) from the field-current nucleation boundaries of magnetic droplet solitons in orthogonal nano-contact spintorque oscillators with Co-x(Ni80Fe20)(1-x), (x = 0 -1), fixed layers. As the perpendicular component of the fixed-layer magnetization plays a central role in governing droplet nucleation, the nucleation boundaries exhibit monotonic shifts towards higher perpendicular magnetic fields when the fixed-layer magnetization mu M-0(s, p) is tuned from 1.04 to 1.7 T. We then extract epsilon and lambda from fits to the nucleation boundaries and find that while epsilon does not vary with composition,lambda increases from 1.5 to 3 with increasing Co content. The analysis of droplet nucleation boundaries is hence a useful tool for the systematic study of both epsilon and lambda as functions of material composition.

Place, publisher, year, edition, pages
American Physical Society, 2018
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-239480 (URN)10.1103/PhysRevApplied.10.054014 (DOI)000449411000004 ()
Funder
Swedish Foundation for Strategic Research Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 29181127

Available from: 2018-11-27 Created: 2018-11-27 Last updated: 2019-08-20Bibliographically approved
Banuazizi, S. A., Sani, S. R., Eklund, A., Naiini, M. M., Mohseni, S. M., Chung, S., . . . Åkerman, J. (2017). Order of magnitude improvement of nano-contact spin torque nano-oscillator performance. Nanoscale, 9(5), 1896-1900
Open this publication in new window or tab >>Order of magnitude improvement of nano-contact spin torque nano-oscillator performance
Show others...
2017 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 9, no 5, p. 1896-1900Article in journal (Refereed) Published
Abstract [en]

Spin torque nano-oscillators (STNO) represent a unique class of nano-scale microwave signal generators and offer a combination of intriguing properties, such as nano sized footprint, ultrafast modulation rates, and highly tunable microwave frequencies from 100 MHz to close to 100 GHz. However, their low output power and relatively high threshold current still limit their applicability and must be improved. In this study, we investigate the influence of the bottom Cu electrode thickness (t(Cu)) in nano-contact STNOs based on Co/Cu/NiFe GMR stacks and with nano-contact diameters ranging from 60 to 500 nm. Increasing t(Cu) from 10 to 70 nm results in a 40% reduction of the threshold current, an order of magnitude higher microwave output power, and close to two orders of magnitude better power conversion efficiency. Numerical simulations of the current distribution suggest that these dramatic improvements originate from a strongly reduced lateral current spread in the magneto-dynamically active region.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2017
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-204731 (URN)10.1039/c6nr07309c (DOI)000395594300017 ()28094381 (PubMedID)2-s2.0-85011392741 (Scopus ID)
Funder
EU, European Research Council, 307144Swedish Research CouncilSwedish Foundation for Strategic Research Knut and Alice Wallenberg Foundation
Note

QC 20170601

Available from: 2017-06-01 Created: 2017-06-01 Last updated: 2018-05-24Bibliographically approved
Xiao, D., Tiberkevich, V., Liu, Y. H., Liu, Y. W., Mohseni, S. M., Chung, S., . . . Zhou, Y. (2017). Parametric autoexcitation of magnetic droplet soliton perimeter modes. Physical Review B, 95(2), Article ID 024106.
Open this publication in new window or tab >>Parametric autoexcitation of magnetic droplet soliton perimeter modes
Show others...
2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 2, article id 024106Article in journal (Refereed) Published
Abstract [en]

Recent experiments performed in current-driven nanocontacts with strong perpendicular anisotropy have shown that spin-transfer torque can drive self-localized spin waves [W. H. Rippard, A. M. Deac, M. R. Pufall, J. M. Shaw, M. W. Keller, S. E. Russek, G. E. W. Bauer, and C. Serpico, Phys. Rev. B 81, 014426 (2010); S. M. Mohseni, S. R. Sani, J. Persson, T. N. A. Nguyen, S. Chung, Y. Pogoryelov, and J. Akerman, Phys. Status Solidi RRL, 5, 432 (2011)], that above a certain intensity threshold can condense into a nanosized and highly nonlinear dynamic state known as a magnetic droplet soliton [S. M. Mohseni, S. R. Sani, J. Persson, T. N. A. Nguyen, S. Chung, Y. Pogoryelov, P. K. Muduli, E. Iacocca, A. Eklund, R. K. Dumas, S. Bonetti, A. Deac, M. A. Hoefer, and J. Akerman, Science 339, 1295 (2013)]. Here we demonstrate analytically, numerically, and experimentally that at sufficiently large driving currents and for a spin polarization direction tilted away from the normal to a nanocontact plane, the circular droplet soliton can become unstable against the excitations in the form of periodic deformations of its perimeter. We also show that these perimeter excitation modes (PEMs) can be excited parametrically when the fundamental droplet soliton precession frequency is close to the double frequency of one of the PEMs. As a consequence, with increasing magnitude of a bias magnetic field the PEMs with progressively higher indices and frequencies can be excited. Full qualitative and partly quantitative agreement with experiment confirm the presented theoretical picture.

Place, publisher, year, edition, pages
American Physical Society, 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-200751 (URN)10.1103/PhysRevB.95.024106 (DOI)000391308200003 ()2-s2.0-85010410354 (Scopus ID)
Note

QC 20170210

Available from: 2017-02-10 Created: 2017-02-10 Last updated: 2017-11-29Bibliographically approved
Mazraati, H., Chung, S., Houshang, A., Dvornik, M., Piazza, L., Qejvanaj, F., . . . Åkerman, J. (2016). Low operational current spin Hall nano-oscillators based on NiFe/W bilayers. Applied Physics Letters, 109(24), Article ID 242402.
Open this publication in new window or tab >>Low operational current spin Hall nano-oscillators based on NiFe/W bilayers
Show others...
2016 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 109, no 24, article id 242402Article in journal (Refereed) Published
Abstract [en]

We demonstrate highly efficient spin Hall nano-oscillators (SHNOs) based on NiFe/beta-W bilayers. Thanks to the very high spin Hall angle of beta-W, we achieve more than a 60% reduction in the auto-oscillation threshold current compared to NiFe/Pt bilayers. The structural, electrical, and magnetic properties of the bilayers, as well as the microwave signal generation properties of the SHNOs, have been studied in detail. Our results provide a promising path for the realization of low-current SHNO microwave devices with highly efficient spin-orbit torque from beta-W. Published by AIP Publishing.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2016
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-201252 (URN)10.1063/1.4971828 (DOI)000391457500025 ()2-s2.0-85006791339 (Scopus ID)
Note

QC 20170215

Available from: 2017-02-15 Created: 2017-02-15 Last updated: 2018-09-07Bibliographically approved
Durrenfeld, P., Gerhard, F., Mohseni, S. M., Ranjbar, M., Sani, S. R., Chung, S., . . . Åkerman, J. (2016). Low-current, narrow-linewidth microwave signal generation in NiMnSb based single-layer nanocontact spin-torque oscillators. Applied Physics Letters, 109(22), Article ID 222403.
Open this publication in new window or tab >>Low-current, narrow-linewidth microwave signal generation in NiMnSb based single-layer nanocontact spin-torque oscillators
Show others...
2016 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 109, no 22, article id 222403Article in journal (Refereed) Published
Abstract [en]

We report on the fabrication of nano-contact spin-torque oscillators based on single layers of the epitaxially grown half-metal NiMnSb with ultralow spin wave damping. We demonstrate magnetization auto-oscillations at microwave frequencies in the 1-3 GHz range in out-of-plane magnetic fields. Threshold current densities as low as 3 x 10(11) A m(-2) are observed as well as minimum oscillation linewidths of 200 kHz, both of which are much lower than the values achieved in conventional metallic spin-valve-based devices of comparable dimensions. These results enable the fabrication of spin transfer torque driven magnonic devices with low current density requirements, improved signal linewidths, and in a simplified single-layer geometry. Published by AIP Publishing.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2016
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-199757 (URN)10.1063/1.4968813 (DOI)000390243100029 ()2-s2.0-85000624517 (Scopus ID)
Note

QC 20170120

Available from: 2017-01-20 Created: 2017-01-16 Last updated: 2017-11-29Bibliographically approved
Organisations

Search in DiVA

Show all publications