Change search
Link to record
Permanent link

Direct link
BETA
Publications (10 of 59) Show all publications
Haidar, M., Awad, A. A., Dvornik, M., Khymyn, R., Houshang, A. & Åkerman, J. (2019). A single layer spin-orbit torque nano-oscillator. Nature Communications, 10, Article ID 2362.
Open this publication in new window or tab >>A single layer spin-orbit torque nano-oscillator
Show others...
2019 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 2362Article in journal (Refereed) Published
Abstract [en]

Spin torque and spin Hall effect nano-oscillators generate high intensity spin wave auto-oscillations on the nanoscale enabling novel microwave applications in spintronics, magnonics, and neuromorphic computing. For their operation, these devices require externally generated spin currents either from an additional ferromagnetic layer or a material with a high spin Hall angle. Here we demonstrate highly coherent field and current tunable microwave signals from nano-constrictions in single 15-20 nm thick permalloy layers with oxide interfaces. Using a combination of spin torque ferromagnetic resonance measurements, scanning micro-Brillouin light scattering microscopy, and micromagnetic simulations, we identify the auto-oscillations as emanating from a localized edge mode of the nano-constriction driven by spin-orbit torques. Our results pave the way for greatly simplified designs of auto-oscillating nano-magnetic systems only requiring single ferromagnetic layers with oxide interfaces.

Place, publisher, year, edition, pages
Nature Publishing Group, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-252967 (URN)10.1038/s41467-019-10120-4 (DOI)000469320900004 ()31142758 (PubMedID)2-s2.0-85067048844 (Scopus ID)
Note

QC 20190812

Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2019-08-12Bibliographically approved
Nguyen, T. N., Fedotova, J., Kasiuk, J., Wu, W.-B. -., Przewoznik, J., Kapusta, C., . . . Åkerman, J. (2019). Enhanced Perpendicular Exchange Bias in Co/Pd Antidot Arrays. Paper presented at 5th International Conference of Asian-Union-of-Magnetics-Societies (IcAUMS), JUN 03-07, 2018, SOUTH KOREA. Journal of Electronic Materials, 48(3), 1492-1497
Open this publication in new window or tab >>Enhanced Perpendicular Exchange Bias in Co/Pd Antidot Arrays
Show others...
2019 (English)In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 48, no 3, p. 1492-1497Article in journal (Refereed) Published
Abstract [en]

Magnetic nanostructures revealing the exchange bias (EB) effect have attracted much interest in recent years due to their promising applications in spintronics, magneticsensing and recording devices with various functionalities. In this paper, we report on the perpendicular exchange bias effect in a multilayered thin film composed of [Co/Pd] ferromagnetic multilayers exchange-coupled to an antiferromagnetic IrMn. The film was deposited on a porous anodized titania template. Influences of the films' surface morphology as well as the order of layers deposited on the EB effect were studied. The enhancements of the EB field H-EB (up to 30%) and the coercive field H-C (two times) were achieved in the nanoporous films relative to their continuous film counterparts, which could be attributed to the specific morphology of the porous surfaces.

Place, publisher, year, edition, pages
SPRINGER, 2019
Keywords
Multilayered Co/Pd thin films, porous TiO2 templates, perpendicular magnetic anisotropy, exchange bias
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-244494 (URN)10.1007/s11664-018-06847-3 (DOI)000457748600028 ()2-s2.0-85058164693 (Scopus ID)
Conference
5th International Conference of Asian-Union-of-Magnetics-Societies (IcAUMS), JUN 03-07, 2018, SOUTH KOREA
Note

QC 20190328

Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-03-29Bibliographically approved
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
Zahedinejad, M., Mazraati, H., Fulara, H., Yue, J., Jiang, S., Awad, A. A. & Åkerman, J. (2018). CMOS compatible W/CoFeB/MgO spin Hall nano-oscillators with wide frequency tunability. Applied Physics Letters, 112(13), Article ID 132404.
Open this publication in new window or tab >>CMOS compatible W/CoFeB/MgO spin Hall nano-oscillators with wide frequency tunability
Show others...
2018 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, no 13, article id 132404Article in journal (Refereed) Published
Abstract [en]

We demonstrate low-operational-current W/Co20Fe60B20/MgO spin Hall nano-oscillators (SHNOs) on highly resistive silicon (HiR-Si) substrates. Thanks to a record high spin Hall angle of the beta-phase W (theta(SH) = -0.53), a very low threshold current density of 3.3 x 10(7) A/cm(2) can be achieved. Together with their very wide frequency tunability (7-28GHz), promoted by a moderate perpendicular magnetic anisotropy, HiR-Si/W/CoFeB based SHNOs are potential candidates for wide-band microwave signal generation. Their CMOS compatibility offers a promising route towards the integration of spintronic microwave devices with other on-chip semiconductor microwave components.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-226793 (URN)10.1063/1.5022049 (DOI)000429072800015 ()2-s2.0-85044750620 (Scopus ID)
Funder
Swedish Foundation for Strategic Research Swedish Research CouncilKnut and Alice Wallenberg FoundationEU, FP7, Seventh Framework Programme, 307144
Note

QC 20180504

Available from: 2018-05-04 Created: 2018-05-04 Last updated: 2018-09-07Bibliographically approved
Chung, S., Le, Q. T., Ahlberg, M., Awad, A. A., Weigand, M., Bykova, I., . . . Åkerman, J. (2018). Direct Observation of Zhang-Li Torque Expansion of Magnetic Droplet Solitons. Physical Review Letters, 120(21), Article ID 217204.
Open this publication in new window or tab >>Direct Observation of Zhang-Li Torque Expansion of Magnetic Droplet Solitons
Show others...
2018 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 120, no 21, article id 217204Article in journal (Refereed) Published
Abstract [en]

Magnetic droplets are nontopological dynamical soli tons that can be nucleated in nanocontact based spin torque nano-oscillators (STNOs) with perpendicular magnetic anisotropy free layers. While theory predicts that the droplet should be of the same size as the nanocontact, its inherent drift instability has thwarted attempts at observing it directly using microscopy techniques. Here, we demonstrate highly stable magnetic droplets in all-perpendicular STNOs and present the first detailed droplet images using scanning transmission X-ray microscopy. In contrast to theoretical predictions, we find that the droplet diameter is about twice as large as the nanocontact. By extending the original droplet theory to properly account for the lateral current spread underneath the nanocontact, we show that the large discrepancy primarily arises from current-in-plane Zhang-Li torque adding an outward pressure on the droplet perimeter. Electrical measurements on droplets nucleated using a reversed current in the antiparallel state corroborate this picture.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-230841 (URN)10.1103/PhysRevLett.120.217204 (DOI)000433040200010 ()29883139 (PubMedID)2-s2.0-85047636345 (Scopus ID)
Note

QC 20180619

Available from: 2018-06-19 Created: 2018-06-19 Last updated: 2018-09-11Bibliographically approved
Nguyen, T. N., Fedotova, J., Kasiuk, J., Bayev, V., Kupreeva, O., Lazarouk, S., . . . Maximenko, A. (2018). Effect of flattened surface morphology of anodized aluminum oxide templates on the magnetic properties of nanoporous Co/Pt and Co/Pd thin multilayered films. Applied Surface Science, 427, 649-655
Open this publication in new window or tab >>Effect of flattened surface morphology of anodized aluminum oxide templates on the magnetic properties of nanoporous Co/Pt and Co/Pd thin multilayered films
Show others...
2018 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 427, p. 649-655Article in journal (Refereed) Published
Abstract [en]

For the first time, nanoporous Al2O3 templates with smoothed surface relief characterized by flattened interpore areas were used in the fabrication of Co/Pd and Co/Pt multilayers (MLs) with strong perpendicular magnetic anisotropy (PMA). Alternating gradient magnetometry (AGM) revealed perfectly conserved PMA in the Co/Pd and Co/Pt porous MLs (antidot arrays) with a ratio of remanent magnetization (Mr) to saturation magnetization (MS) of about 0.99, anisotropy fields (Ha) of up to 2.6 kOe, and a small deviation angle of 8° between the easy magnetization axis and the normal to the film surface. The sufficient magnetic hardening of the porous MLs with enhanced coercive field HC of up to ∼1.9 kOe for Co/Pd and ∼1.5 kOe for Co/Pt MLs, as compared to the continuous reference samples (∼1.5–2 times), is associated with the pinning of the magnetic moments on the nanopore edges. Application of the Stoner–Wohlfarth model for fitting the experimental M/MS(H) curves yielded clear evidence of the predominantly coherent rotation mechanism of magnetization reversal in the porous films.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Antidots, Co/Pd multilayers, Co/Pt multilayers, Percolated perpendicular media, Perpendicular magnetic anisotropy, Porous anodic aluminum oxide templates, Aluminum, Anisotropy, Anodic oxidation, Curve fitting, Magnetic anisotropy, Magnetic moments, Magnetic multilayers, Magnetism, Magnetization, Magnetization reversal, Multilayers, Oxide films, Oxides, Saturation magnetization, Co/Pt multilayer, Perpendicular media, Cobalt
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-216812 (URN)10.1016/j.apsusc.2017.08.238 (DOI)000415219100083 ()2-s2.0-85029377937 (Scopus ID)
Funder
Swedish Foundation for Strategic Research Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 20171207

Available from: 2017-12-05 Created: 2017-12-05 Last updated: 2017-12-07Bibliographically 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
Mazraati, H., Zahedinejad, M. & Åkerman, J. (2018). Improving the magnetodynamical properties of NiFe/Pt bilayers through Hf dusting [Letter to the editor]. Applied Physics Letters, 113(9), 092401
Open this publication in new window or tab >>Improving the magnetodynamical properties of NiFe/Pt bilayers through Hf dusting
2018 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 113, no 9, p. 092401-Article in journal, Letter (Refereed) Published
Abstract [en]

We investigate the effect of hafnium (Hf) dusting on the magnetodynamical properties of NiFe/Pt bilayers using spin-torque-induced ferromagnetic resonance measurements on 6 μm wide microstrips on high-resistive Si substrates. Based on two series of NiFe(tNiFe)/Hf(tHf)/Pt(5) stacks, we first demonstrate that the zero-current magnetodynamic properties of the devices benefit from Hf dusting: (i) the effective magnetization of the NiFe layer increases by 4%–8% with Hf present and (ii) the damping α decreases linearly with tHf by up to 40%. The weaker anisotropic magnetoresistance (AMR≈0.3%–0.4%) of the 3 nm NiFe series is largely unaffected by the Hf, while the stronger AMR of the 5 nm NiFe series drops from 0.7% to 0.43% with increasing tHf. We find that the spin Hall efficiency ξSH is independent of the NiFe thickness, remaining unaffected (ξSH = 0.115) up to tHf = 0.4 nm and then decreasing linearly for higher tHf. The different trends of α and ξSH suggest that there is an optimum Hf thickness (≈0.4 nm) for which the threshold current for auto-oscillation should have a minimum, while the much lower damping should improve mutual synchronization. Our results also indicate that the spin-orbit torque is entirely damping-like with no field-like torque component. Finally, the internal spin Hall angle of Pt is estimated to be θSH = 0.22 by calculating the transparency of the interface.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2018
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-234311 (URN)10.1063/1.5026232 (DOI)2-s2.0-85052729304 (Scopus ID)
Note

QC 20180911

Available from: 2018-09-06 Created: 2018-09-06 Last updated: 2018-09-11Bibliographically approved
Tiwari, D., Sharma, R., Heinonen, O. G., Åkerman, J. & Muduli, P. K. (2018). Influence of MgO barrier quality on spin-transfer torque in magnetic tunnel junctions. Applied Physics Letters, 112(2), Article ID 022406.
Open this publication in new window or tab >>Influence of MgO barrier quality on spin-transfer torque in magnetic tunnel junctions
Show others...
2018 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, no 2, article id 022406Article in journal (Refereed) Published
Abstract [en]

We studied the bias dependence of spin transfer torque in the MgO-based magnetic tunnel junction using a field-modulated spin torque ferromagnetic resonance measurement technique for three devices with tunneling magnetoresistances (MRs) of 60%, 67%, and 73%, respectively. The devices with a lower MR ratio showed the presence of multiple modes, while the device with higher MR (73%) showed a single resonance mode. We found a lower out-of-plane torkance in our devices compared to the in-plane torkance. The out-of-plane torque is linear with applied bias, while the bias dependence of in-plane torque shows a strong dependence on the MR ratio and hence the barrier quality.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2018
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-221787 (URN)10.1063/1.5005893 (DOI)000422965000031 ()2-s2.0-85040519728 (Scopus ID)
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Note

QC 20180125

Available from: 2018-01-25 Created: 2018-01-25 Last updated: 2018-02-02Bibliographically approved
Burgos-Parra, E., Bukin, N., Redjai Sani, S., Figueroa, A. I., Beutier, G., Dupraz, M., . . . Ogrin, F. Y. (2018). Investigation of magnetic droplet solitons using x-ray holography with extended references. Scientific Reports, 8, Article ID 11533.
Open this publication in new window or tab >>Investigation of magnetic droplet solitons using x-ray holography with extended references
Show others...
2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 11533Article in journal (Refereed) Published
Abstract [en]

A dissipative magnetic soliton, or magnetic droplet, is a structure that has been predicted to exist within a thin magnetic layer when non-linearity is balanced by dispersion, and a driving force counteracts the inherent damping of the spin precession. Such a soliton can be formed beneath a nano-contact (NC) that delivers a large spin-polarized current density into a magnetic layer with perpendicular magnetic anisotropy. Although the existence of droplets has been confirmed from electrical measurements and by micromagnetic simulations, only a few attempts have been made to directly observe the magnetic landscape that sustains these structures, and then only for a restricted set of experimental parameter values. In this work we use and x-ray holography technique HERALDO, to image the magnetic structure of the [ Co/ Ni] x4 multilayer within a NC orthogonal pseudo spin-valve, for different range of magnetic fields and injected electric currents. The magnetic configuration imaged at -33 mA and 0.3 T for devices with 90 nm NC diameter reveals a structure that is within the range of current where the droplet soliton exist based on our electrical measurements and have it is consistent with the expected size of the droplet (similar to 100 nm diameter) and its spatial position within the sample. We also report the magnetisation configurations observed at lower DC currents in the presence of fields (0-50 mT), where it is expected to observe regimes of the unstable droplet formation.

Place, publisher, year, edition, pages
Nature Publishing Group, 2018
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-233289 (URN)10.1038/s41598-018-29856-y (DOI)000440411300018 ()30069062 (PubMedID)2-s2.0-85050962853 (Scopus ID)
Funder
Swedish Foundation for Strategic Research EU, European Research Council, 307144Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 20180816

Available from: 2018-08-16 Created: 2018-08-16 Last updated: 2018-08-16Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3513-6608

Search in DiVA

Show all publications