kth.sePublikationer
Ändra sökning
Avgränsa sökresultatet
1 - 19 av 19
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Ahlberg, Martina
    et al.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Chung, Sunjae
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;Korea Natl Univ Educ, Dept Phys Educ, Cheongju 28173, South Korea..
    Jiang, Sheng
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Univ Gothenburg, Dept Phys.
    Frisk, Andreas
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Khademi, Maha
    Shahid Beheshti Univ, Dept Phys, Tehran 1983969411, Iran..
    Khymyn, Roman
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Awad, Ahmad A.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Le, Quang Tuan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Univ Gothenburg, Dept Phys.
    Mazraati, Hamid
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. NanOsc AB, S-16440 Kista, Sweden..
    Mohseni, Majid
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Shahid Beheshti Univ, Dept Phys, Tehran 1983969411, Iran..
    Weigand, Markus
    Max Planck Inst Intelligent Syst, Stuttgart, Germany..
    Bykova, Iuliia
    Max Planck Inst Intelligent Syst, Stuttgart, Germany..
    Gross, Felix
    Max Planck Inst Intelligent Syst, Stuttgart, Germany..
    Goering, Eberhard
    Max Planck Inst Intelligent Syst, Stuttgart, Germany..
    Schutz, Gisela
    Max Planck Inst Intelligent Syst, Stuttgart, Germany..
    Grafe, Joachim
    Max Planck Inst Intelligent Syst, Stuttgart, Germany..
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Univ Gothenburg, Dept Phys.
    Freezing and thawing magnetic droplet solitons2022Ingår i: Nature Communications, E-ISSN 2041-1723, Vol. 13, nr 1, artikel-id 2462Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Magnetic droplets are a type of non-topological magnetic soliton, which are stabilised and sustained by spin-transfer torques for instance. Without this, they would collapse. Here Ahlberg et al show that by decreasing the applied magnetic field, droplets can be frozen, forming a static nanobubble Magnetic droplets are non-topological magnetodynamical solitons displaying a wide range of complex dynamic phenomena with potential for microwave signal generation. Bubbles, on the other hand, are internally static cylindrical magnetic domains, stabilized by external fields and magnetostatic interactions. In its original theory, the droplet was described as an imminently collapsing bubble stabilized by spin transfer torque and, in its zero-frequency limit, as equivalent to a bubble. Without nanoscale lateral confinement, pinning, or an external applied field, such a nanobubble is unstable, and should collapse. Here, we show that we can freeze dynamic droplets into static nanobubbles by decreasing the magnetic field. While the bubble has virtually the same resistance as the droplet, all signs of low-frequency microwave noise disappear. The transition is fully reversible and the bubble can be thawed back into a droplet if the magnetic field is increased under current. Whereas the droplet collapses without a sustaining current, the bubble is highly stable and remains intact for days without external drive. Electrical measurements are complemented by direct observation using scanning transmission x-ray microscopy, which corroborates the analysis and confirms that the bubble is stabilized by pinning.

  • 2.
    Chung, Sunjae
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Department of Physics, University of Gothenburg.
    Jiang, Sheng
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Eklund, Anders
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektronik och inbyggda system, Integrerade komponenter och kretsar.
    Iacocca, Ezio
    Department of Applied Mathematics, University of Colorado.
    Le, Quang Tuan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Mazraati, Hamid
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Mohseni, Seyed Majid
    Department of Physics, Shahid Beheshti University, Tehran 19839, Iran.
    Sani, Sohrab Redjai
    Department of Physics and Astronomy, Uppsala University,.
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Effect of canted magnetic field on magnetic droplet nucleation boundariesManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    The influence on magnetic droplet nucleation boundaries by canted magnetic elds are investigated and reported. The nucleation boundary condition, In = αAH + BH + C, is determined at different canted angles (0°< θH<20°) using magnetoresistance (MR) and microwave measurements in nanocontact spintorque oscillators (NC-STOs). As θH increased, the nucleation boundary shifts gradually towards higher In and H. The coefficient B of the nucleation boundary equation also nearly doubled as θH increases. On theother hand, the coefficient αA remained constant for all values of θH. These observations can be explained by considering the drift instability of magnetic droplets and the different tilt behaviour of the Co fixed layer induced by different θH.

  • 3.
    Chung, Sunjae
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Le, Quang Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Ahlberg, Martina
    Department of Physics, University of Gothenburg.
    Awad, Ahmad A.
    Department of Physics, University of Gothenburg.
    Mazraati, Hamid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. NanOsc AB.
    Houshang, Afshin
    Department of Physics, University of Gothenburg.
    Jiang, Sheng
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Nguyen, Thi Ngoc Anh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Institute of Materials Science, Vietnam Academy of Science and Technology.
    Dumas, Randy K.
    Department of Physics, University of Gothenburg.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden; NanOsc AB, Sweden.
    Magnetic droplet solitons in all-perpendicular nano-contact spin torque oscillatorsManuskript (preprint) (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    Spin-torque-generated magnetic droplets are nontopological solitons that have both dynamic and static characteristics. Although   theoretical studies of these droplets originally dealt with  an all-perpendicular magnetic system, all experimental demonstrations have so far relied on orthogonal spin valve structures that require a rather strong magnetic field to nucleate the droplet. Here, for the first time, we show the nucleation and sustained operation of magnetic droplets under a low magnetic field using nanocontact spin-torque oscillators (NC-STO),  both the free Co/Ni and fixed Co/Pd multilayers of which have strong perpendicular magnetic anisotropy. Droplet nucleation is observed as a change in the NC-STO resistance and the appearance of significant broadband microwave signal generation below 1 GHz. We also observe another important phenomenon in which the nucleated magnetic droplet can transform into a skyrmionic nanobubble in the low-field regime. Both magnetic droplet solitons and skyrmionic nanobubbles have been studied in detail using micromagnetic simulation.

  • 4.
    Chung, Sunjae
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Le, Quang Tuan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Ahlberg, Martina
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;NanOsc AB, S-16440 Kista, Sweden..
    Awad, Ahmad A.
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;NanOsc AB, S-16440 Kista, Sweden..
    Weigand, Markus
    Max Planck Inst Intelligent Syst, D-70569 Stuttgart, Germany..
    Bykova, Iuliia
    Max Planck Inst Intelligent Syst, D-70569 Stuttgart, Germany..
    Khymyn, Roman
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Dvornik, Mykola
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Mazraati, Hamid
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. NanOsc AB, S-16440 Kista, Sweden..
    Houshang, Afshin
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;NanOsc AB, S-16440 Kista, Sweden..
    Jiang, Sheng
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Anh Nguyen, T. N.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.; Vietnam Acad Sci & Technol, Inst Mat Sci, Lab Magnetism & Superconduct, 18 Hoang Quoc Viet, Hanoi 122300, Vietnam..
    Goering, Eberhard
    Max Planck Inst Intelligent Syst, D-70569 Stuttgart, Germany..
    Schuetz, Gisela
    Max Planck Inst Intelligent Syst, D-70569 Stuttgart, Germany..
    Graefe, Joachim
    Max Planck Inst Intelligent Syst, D-70569 Stuttgart, Germany..
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;NanOsc AB, S-16440 Kista, Sweden..
    Direct Observation of Zhang-Li Torque Expansion of Magnetic Droplet Solitons2018Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 120, nr 21, artikel-id 217204Artikel i tidskrift (Refereegranskat)
    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.

  • 5.
    Jiang, Sheng
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. NanOsc AB, S-16440 Kista, Sweden..
    Chung, Sunjae
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Diez, Liza Herrera
    Univ Paris Saclay, Univ Paris Sud, CNRS, Inst Elect Fondamentale, F-91405 Orsay, France..
    Le, Quang Tuan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.
    Magnusson, Fredrik
    NanOsc AB, S-16440 Kista, Sweden..
    Ravelosona, Dafine
    Univ Paris Saclay, Univ Paris Sud, CNRS, Inst Elect Fondamentale, F-91405 Orsay, France.;Spin Ion Technol, 28 Rue Gen Leclerc, F-78000 Versailles, France..
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. NanOsc AB, S-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Tuning the magnetodynamic properties of all-perpendicular spin valves using He+ irradiation2018Ingår i: AIP Advances, E-ISSN 2158-3226, Vol. 8, nr 6, artikel-id 065309Artikel i tidskrift (Refereegranskat)
    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%.

  • 6.
    Jiang, Sheng
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Chung, Sunjae
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Department of Physics and Astronomy, Uppsala University.
    Le, Quang Tuan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Diez, Liza Herrera
    Institut d'Electronique Fondamentale, CNRS, Universite Paris-Sud, Universite Paris-Saclay.
    Houshang, Afshin
    Department of Physics, University of Gothenburg.
    Zahedinejad, Mohammad
    Department of Physics, University of Gothenburg.
    Ravelosona, Dafine
    Institut d'Electronique Fondamentale, CNRS, Universite Paris-Sud, Universite Paris-Saclay.
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. Department of Physics, University of Gothenburg.
    Experimental evidence of tunable nonlinearity in He+ irradiated spin-torque oscillatorsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Spin-torque nano-oscillators (STNOs) are among the most promising candidates for nanoscale broadband microwave generators. Before this application can be realized, however, enormous efforts are required of researchers to meet the commercial requirements of high-frequency tunability, high power, and narrow linewidth. As the performance of STNOs is mainly attributed to the nonlinearity on the basis of nonlinear auto-oscillator theory, we here systematically study how this nonlinearity is affected by the free-layer's effective magnetization Meff (i.e., the perpendicular magnetic anisotropy, PMA) in STNOs. The PMA is gradually tuned by using different fluences of He+ irradiation. Consequently, the nonlinearity can be continuously tailored from positive to negative. In addition, due to the almost zero nonlinearity, the linewidth shows an improvement of more than two orders of magnitude. This experimental observation is in strong agreement with the theory of nonlinear auto-oscillators. Our study not only confirms the theoretical prediction of nonlinearity, but also indicates the route to be taken towards realizing commercial microwave generators.

  • 7.
    Jiang, Sheng
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Chung, Sunjae
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Le, Quang Tuan
    Mazraati, Hamid
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Houshang, Afshin
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Using magnetic droplet nucleation to determine the spin torque effciency and asymmetry in Cox(NiFe)1-x thin filmsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    We demonstrate how to extract the material dependent spin torque efficiency (ε) and asymmetry(λ) from the eld{current nucleation boundaries of magnetic droplet solitons in orthogonal nanocontacts in-torque oscillators with Cox(Ni80Fe20)1-x, (x=0{1), fixed layers. As the perpendicular component of the xed layer magnetization plays a central role in governing droplet nucleation, the nucleation boundaries exhibit monotonic shifts towards higher perpendicular magnetic elds when the xed layer magnetization μ0Ms,p is tuned from 1.04 to 1.7 T. We then extract ε and λ from tsto the nucleation boundaries and nd that while ε does not vary with composition, λ increases from1.5 to 3 with increasing Co content. The analysis of droplet nucleation boundaries is hence a useful tool for the systematic study of both ε and λ as functions of material composition.

  • 8.
    Jiang, Sheng
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. NanOsc AB, S-16440 Kista, Sweden..
    Etesami, Seyyed Ruhollah
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Chung, Sunjae
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Le, Quang Tuan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Houshang, Afshin
    NanOsc AB, S-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Impact of the Oersted Field on Droplet Nucleation Boundaries2018Ingår i: IEEE Magnetics Letters, ISSN 1949-307X, E-ISSN 1949-3088, Vol. 9, artikel-id 3104304Artikel i tidskrift (Refereegranskat)
    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.

  • 9.
    Jiang, Sheng
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Khymyn, Roman
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Chung, Sunjae
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Korea Natl Univ Educ, Dept Phys Educ, Cheongju 28173, South Korea..
    Le, Quang Tuan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Diez, Liza Herrera
    Univ Paris Saclay, Ctr Nanosci & Nanotechnol, CNRS, F-91120 Palaiseau, France..
    Houshang, Afshin
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;NanOsc AB, S-16440 Kista, Sweden..
    Zahedinejad, Mohammad
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Ravelosona, Dafine
    Univ Paris Saclay, Ctr Nanosci & Nanotechnol, CNRS, F-91120 Palaiseau, France.;Spin Ion Technol, 10 Blvd Thomas Gobert, F-91120 Palaiseau, France..
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;NanOsc AB, S-16440 Kista, Sweden..
    Reduced spin torque nano-oscillator linewidth using He+ irradiation2020Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 116, nr 7, artikel-id 072403Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We demonstrate an approach for improving the spectral linewidth of a spin torque nano-oscillator (STNO). Using He + ion irradiation, we tune the perpendicular magnetic anisotropy (PMA) of the STNO free layer such that its easy axis is gradually varied from strongly out-of-plane to moderate in-plane. As the PMA impacts the non-linearity N of the STNO, we can, in this way, control the threshold current, the current tunability of the frequency, and, in particular, the STNO linewidth, which dramatically improves by two orders of magnitude. Our results are in good agreement with the theory for nonlinear auto-oscillators, confirm theoretical predictions of the role of the nonlinearity, and demonstrate a straightforward path toward improving the microwave properties of STNOs.

  • 10.
    Le, Quang Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Magnetodynamics in Spin Valves and Magnetic Tunnel Junctions with Perpendicular and Tilted Anisotropies2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Effekter av spinnvridmoment (STT) har fört spinntroniken allt närmare praktiska elektroniska tillämpningar, såsom MRAM och den spinntroniska mikrovågsoscillatorn (STO), och har blivit ett allt mer attraktivt forskningsområde inom spinndynamik. Användning av material med vinkelrät magnetisk anisotropi (PMA) i sådana tillämpningar erbjuder flera stora fördelar, såsom låg strömförbrukning och funktion vid låga fält i kombination med hög termisk stabilitet. Den utbyteskoppling (”exchange bias”) en PMA-tunnfilm utövar på ett intilliggande skikt med magnetisk anisotropi i planet (IMA) kan få IMA-magnetiseringsriktningen att vridas ut ur planet, vilket ger en materialstack med en effektivt sett lutande magnetisk anisotropi. Lutningsvinkeln kan manipuleras med både inre materialparametrar, såsom PMA och mättningsmagnetisering, och yttre parametrar, såsom skikttjocklekarna.

    STO:er kan tillverkas som flera olika typer - som en nanokontaktsöppning på en s.k. mesa av en deponerad pseudospinnventilstruktur (PSV) eller som en nanotråd etsad ur en magnetisk tunnlingsövergång (MTJ) –och bestå av mycket reproducerbar PMA eller av skikt med på förhand bestämt lutning av dess magnetiska anisotropi.

    MTJ-STO:er av CoFeB med helt vinkelrät anisotropi visar högfrekvent mikrovågsgenerering med extremt stort frekvensomfång hos strömstyrningen, detta vid låg biasering. Mätning och analys av spinnvridmoments-ferromagnetisk resonans (ST-FMR) avslöjade ett biasberoende hos spinnvridmomentskomponenter, vilket indikerar en stor potential för direkt gate-spänningsstyrda STO:er.

    I helt vinkelräta PSV-STO:er observerades magnetiska droppar under nanokontaktområdet vid låg drivström och lågt pålagt fält. Dessutom erhölls preliminära resultat av mikrovågssjälvsvängning och av s.k. ”droplet solitons” hos PSV-STO:er med lutande polarisator. Dessa är lovande och skulle vara värda att undersökas i ytterligare studier av STT-driven spinndynamik.

    Ladda ner fulltext (pdf)
    Tuan Le - Thesis
  • 11.
    Le, Quang Tuan
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Eklund, Anders
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Banuazizi, Seyed Amir Hossein
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Fallahi, Vahid Fallahi
    Faculty of Physics, Amirkabir University of Technology.
    Nguyen, Thi Ngoc Anh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Yamanouchi, M.
    Laboratory for Nanoelectronics and Spintronics, RIEC, Tohoku University.
    Enobio, Eli C. I.
    Center for Spintronics Integrated Systems, Tohoku University.
    Ikeda, S.
    Laboratory for Nanoelectronics and Spintronics, RIEC, Tohoku University.
    Ohno, Hideo
    Laboratory for Nanoelectronics and Spintronics, RIEC, Tohoku University.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden; NanOsc AB, Sweden.
    Ultra-high frequency tunability in low-current and low-field spin-torque oscillators based on perpendicular magnetic tunnel junctionsManuskript (preprint) (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    We demonstrate ultra-high frequency tunability of up to 4.4 GHz/mA, and low threshold currents of about -21 $\mu$A, in spin-torque oscillators based on CoFeB/MgO/CoFeB magnetic tunnel junctions, in which both free and fixed layers have perpendicular magnetic anisotropy (PMA). By using different thicknesses of the two CoFeB layers, their individual PMA strengths can be tailored to achieve significant relative misalignment of their respective magnetizations in moderate in-plane fields. We observe a broad maximum in both the device resistance and the generated microwave power around maximum misalignment. Maximum frequency tunability is observed at low-to-moderate fields and decrease rapidly after maximum misalignment.

  • 12.
    Le, Quang Tuan
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Mazraati, Hamid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Nguyen, Thi Ngoc Anh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Institute of Materials Science, Vietnam Academy of Science and Technology.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden; NanOsc AB, Sweden.
    Bias dependence of parallel spin torque in all-perpendicular magnetic tunnel junction nanodevicesManuskript (preprint) (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    We performed spin-torque ferromagnetic resonance measurements on spin-torque oscillators based on CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs), with both free and fixed layers having perpendicular magnetic anisotropy, under the application of an in-plane field. A dc current between near-zero and -250 $\mu{A}$ was introduced to investigate the influence of spin-transfer torque effects on the asymmetric and symmetric components of the output voltage. Both components showed a minimum at a misalignment of about 30$^\circ$ between the magnetization of the two CoFeB layers, indicating a strong electric-field effect. We also found that the bias dependence of the spin-torque terms is in contrast to that of in-plane anisotropy CoFeB MTJs.

  • 13.
    Mazraati, Hamid
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Houshang, Afshin
    Dvornik, Mykola
    Piazza, Luca
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Qejvanaj, Fatjon
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Jiang, Sheng
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Le, Quang Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Low operational current spin Hall nano-oscillators based on NiFe/W bilayers2016Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 109, nr 24, artikel-id 242402Artikel i tidskrift (Refereegranskat)
    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.

    Ladda ner fulltext (pdf)
    fulltext
  • 14.
    Mazraati, Hamid
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. NanOsc AB.
    Le, Quang Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Awad, Ahmad A.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Hirayama, Eriko
    Ikeda, Shoji
    Matsukura, Fumihiro
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden; NanOsc AB, Sweden.
    Free- and reference-layer magnetization modes vs.~in-plane magnetic field in  a magnetic tunnel junction with perpendicular magnetic easy axis2016Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    We study the magnetodynamic modes of a magnetic tunnel junction with perpendicular magnetic easy axis (p-MTJ) in in-plane magnetic fields using device-level ferromagnetic resonance spectroscopy. We compare our experimental results to those of micromagnetic simulations of the entire p-MTJ. Using an iterative approach to determine the material parameters that best fit our experiment, we find excellent agreement between experiments and simulations in both the static magnetoresistance and magnetodynamics in the free and reference layers. From the micromagnetic simulations, we determine the spatial mode profiles, the localization of the modes and, as a consequence, their distribution in the frequency domain due to the inhomogeneous internal field distribution inside the p-MTJ under different applied field regimes. We also conclude that the excitation mechanism is a combination of the microwave voltage modulated perpendicular magnetic anisotropy, the microwave Oersted field, and the spin-transfer torque generated by the microwave current.

    Ladda ner fulltext (pdf)
    fulltext
  • 15.
    Mazraati, Hamid
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. NanOsc AB, Sweden.
    Le, Tuan Q.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Awad, Ahmad A.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. University of Gothenburg, Sweden.
    Hirayama, Eriko
    Ikeda, Shoji
    Matsukura, Fumihiro
    Ohno, Hideo
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. NanOsc AB, Sweden; University of Gothenburg, Sweden.
    Free- and reference-layer magnetization modes versus in-plane magnetic field in a magnetic tunnel junction with perpendicular magnetic easy axis2016Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, nr 10, artikel-id 104428Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the magnetodynamic modes of a magnetic tunnel junction with perpendicular magnetic easy axis (p-MTJ) in in-plane magnetic fields using device-level ferromagnetic resonance spectroscopy. We compare our experimental results to those of micromagnetic simulations of the entire p-MTJ. Using an iterative approach to determine the material parameters that best fit our experiment, we find excellent agreement between experiments and simulations in both the static magnetoresistance and magnetodynamics in the free and reference layers. From the micromagnetic simulations, we determine the spatial mode profiles, the localization of the modes and, as a consequence, their distribution in the frequency domain due to the inhomogeneous internal field distribution inside the p-MTJ under different applied field regimes. We also conclude that the excitation mechanism is a combination of the microwave voltage modulated perpendicular magnetic anisotropy, the microwave Oersted field, and the spin-transfer torque generated by the microwave current.

  • 16. Mukherjee, Sumanta
    et al.
    Knut, Ronny
    Mohseni, S. Majid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Shahid Beheshti Univ, Iran.
    Nguyen, T. N. Anh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. VNU HCM, Vietnam.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Le, Quang Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Persson, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sahoo, Anindita
    Hazarika, Abhijit
    Pal, Banabir
    Thiess, Sebastian
    Gorgoi, Mihaela
    Kumar, P. S. Anil
    Drube, Wolfgang
    Karis, Olof
    Sarma, D. D.
    Role of boron diffusion in CoFeB/MgO magnetic tunnel junctions2015Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, nr 8, artikel-id 085311Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Several scientific issues concerning the latest generation read heads for magnetic storage devices, based on CoFeB/MgO/CoFeBmagnetic tunnel junctions (MTJs) are known to be controversial, including such fundamental questions as to the behavior and the role of B in optimizing the physical properties of these devices. Quantitatively establishing the internal structures of several such devices with different annealing conditions using hard x-ray photoelectron spectroscopy, we resolve these controversies and establish that the B diffusion is controlled by the capping Ta layer, though Ta is physically separated from the layer with B by several nanometers. While explaining this unusual phenomenon, we also provide insight into why the tunneling magnetoresistance (TMR) is optimized at an intermediate annealing temperature, relating it to B diffusion, coupled with our studies based on x-ray diffraction and magnetic studies.

  • 17.
    Nguyen, T. N. Anh
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Vietnam Natl Univ Ho Chi Minh City, Vietnam.
    Knut, R.
    Fallahi, V.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Le, Quang Tuan Le
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Mohseni, Seyed Majid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Shahid Beheshti Univ, Iran.
    Karis, O.
    Peredkov, S.
    Dumas, R. K.
    Miller, Casey W.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden; NanOsc AB, Sweden.
    Depth-Dependent Magnetization Profiles of Hybrid Exchange Springs2014Ingår i: PHYS REV APPL, ISSN 2331-7019, Vol. 2, nr 4, s. 044014-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on the magnetization depth profile of a hybrid exchange-spring system in which a Co/Pd multilayer with perpendicular anisotropy is coupled to a CoFeB thin film with in-plane anisotropy. The competition between these two orthogonal anisotropies promotes a strong depth dependence of the magnetization orientation. The angle of the magnetization vector is sensitive both to the strength of the individual anisotropies and to the local exchange constant and is thus tunable by changing the thickness of the CoFeB layer and by substituting Ni for Pd in one layer of the Co/Pd stack. The resulting magnetic depth profiles are directly probed by element-specific x-ray magnetic circular dichroism of the Fe and Ni layers located at different average depths. The experimental results are corroborated by micromagnetic simulations.

  • 18.
    Nguyen, Thi Ngoc Anh
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Vietnam Natl Univ, Vietnam.
    Fallahi, Vahid
    Le, Quang Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Chung, Sunjea
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Mohseni, Seyed Majid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Shahid Beheshti Univ, Iran.
    Dumas, Randy K.
    Miller, Casey W.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Investigation of the Tunability of the Spin Configuration Inside Exchange Coupled Springs of Hard/Soft Magnets2014Ingår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, nr 6, s. 2004906-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Magnetic multilayer (ML) structures comprising a perpendicular magnetic anisotropy (PMA) layer coupled to an in-plane magnetic anisotropy (IMA) layer are promising materials for zero/low field operating spin-torque oscillators and bit patterned recording media. The magnetization tilt angle can be easily tuned by varying the IMA layer thickness due to the competition between PMA and IMA layers. To explore the underlying magnetization reversal mechanism and to further understand the control of tilt angle and uniformity of the magnetization, the IMA (NiFe, Co, and CoFeB)/PMA (Co/Pd MLs) exchange spring systems are systematically studied. Experimental data obtained from magnetometry show good agreement with 1-D micromagnetic simulations, allowing us to design tunable exchange coupled spring as a function of IMA thickness.

  • 19. Qejvanaj, Fatjon
    et al.
    Zubair, M.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Persson, A.
    Mohseni, S. M.
    Fallahi, V.
    Sani, Sohrab Redjai
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Le, Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Magnusson, F.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Thick Double-Biased IrMn/NiFe/IrMn Planar Hall Effect Bridge Sensors2014Ingår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, nr 11, artikel-id 4006104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we present a new material stack for planar Hall effect bridge (PHEB) sensors and a detailed investigation of the sensitivity and noise properties of PHEB sensors made from these. The sputter deposited material stack was based on a ferromagnetic (FM) NiFe sensing layer surrounded by two layers of anti-FM IrMn. This material stack enables implementation of a thick NiFe layer without loss of sensitivity. We present an improvement in detectivity in the PHEB by changing the shape and the materials of the corners between the sensors in a meander shape. A significant reduction of noise also comes from the thick NiFe layer, due to the reduced resistance of the sensor.

1 - 19 av 19
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf