Profiles

Stefano Bonetti

Stefano Bonetti

Forskare

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Arbetar vid Fysikum
Telefon 08-553 786 55
E-post stefano.bonetti@fysik.su.se
Besöksadress Roslagstullsbacken 21
Rum A3:1007
Postadress Fysikum 106 91 Stockholm

Om mig

 

Arbetsliv

2017 - nu 

Docent, Forskare (med rätt att ansöka om befordran till professor)
Fysikum, Stockholms universitet
2014 - 2016 Forskare
Fysikum, Stockholms universitet
2012 - 2014 Postdoktor
Department of Physics, Stanford University

 

Utmärkelser och Anslag

2018 - 2022 Wallenberg Academy Fellow
Projekt: Ultrasnabb och koherent kontroll av kvantmaterial
2017 - 2021 ERC Starting Grant
Projekt: Understanding the speed limits of magnetism
2015 - 2019 International Career Grant
COFUND från Vetenskapsrådet och Marie Skłodowska Curie Actions
Projekt: THz spinnstyrning
2015 Postdoctoral Award for Best Presentation of Research, 2015 Winner
American Vacuum Society - Magnetic Interfaces and Nanostructure Division
2012 - 2014 MaxIV Postdoctoral Fellowship
Knut and Alice Wallenberg Stiftelse
2012 - 2014 International Postdoc
Vetenskapsrådet

 

Utbildning

2006 - 2011 Doktorsexamen, Materialfysik, KTH – Kungliga Tekniska Högskolan, Stockholm, Sverige.
2004 - 2006 Civilingenjörsexamen, Teknisk Fysik, KTH – Kungliga Tekniska Högskolan, Stockholm, Sverige.
2001 - 2004 Kandidatexamen, Teknisk Fysik, “Politecnico di Milano” Technical University, Italien.

 

Undervisning

Kvantmekanik, FK5020

The course is taught using research-based principles for effective teaching.


Forskning

As an experimental physicist, my research is devoted to ultrafast dynamics and transport in condensed matter, in particular addressing spin-dependent phenomena.

My group's current research efforts focus on the use of strong THz radiation to drive non-equilibrium dynamics in materials, probed with femtosecond IR laser pulses or femtosecond x-ray pulses generated at free electron lasers

 

Publikationer

I urval från Stockholms universitets publikationsdatabas
  • 2017. Stefano Bonetti. Journal of Physics 29 (13)

    Understanding how spins move in time and space is the aim of both fundamental and applied research in modern magnetism. Over the past three decades, research in this field has led to technological advances that have had a major impact on our society, while improving the understanding of the fundamentals of spin physics. However, important questions still remain unanswered, because it is experimentally challenging to directly observe spins and their motion with a combined high spatial and temporal resolution. In this article, we present an overview of the recent advances in x-ray microscopy that allow researchers to directly watch spins move in time and space at the microscopically relevant scales. We discuss scanning x-ray transmission microscopy (STXM) at resonant soft x-ray edges, which is available at most modern synchrotron light sources. This technique measures magnetic contrast through the x-ray magnetic circular dichroism (XMCD) effect at the resonant absorption edges, while focusing the x-ray radiation at the nanometre scale, and using the intrinsic pulsed structure of synchrotron-generated x-rays to create time-resolved images of magnetism at the nanoscale. In particular, we discuss how the presence of spin currents can be detected by imaging spin accumulation, and how the magnetisation dynamics in thin ferromagnetic films can be directly imaged. We discuss how a direct look at the phenomena allows for a deeper understanding of the the physics at play, that is not accessible to other, more indirect techniques. Finally, we present an overview of the exciting opportunities that lie ahead to further understand the fundamentals of novel spin physics, opportunities offered by the appearance of diffraction limited storage rings and free electron lasers.

  • 2017. M. Kozina (et al.). Applied Physics Letters 110 (8)

    We report local field strength enhancement of single-cycle terahertz (THz) pulses in an ultrafast time-resolved x-ray diffraction experiment. We show that patterning the sample with gold microstructures increases the THz field without changing the THz pulse shape or drastically affecting the quality of the x-ray diffraction pattern. We find a five-fold increase in THz-induced x-ray diffraction intensity change in the presence of microstructures on a SrTiO3 thin-film sample.

  • 2016. Stefano Bonetti (et al.). Physical Review Letters 117 (8)

    We use single-cycle THz fields and the femtosecond magneto-optical Kerr effect to, respectively, excite and probe the magnetization dynamics in two thin-film ferromagnets with different lattice structures: crystalline Fe and amorphous CoFeB. We observe Landau-Lifshitz-torque magnetization dynamics of comparable magnitude in both systems, but only the amorphous sample shows ultrafast demagnetization caused by the spin-lattice depolarization of the THz-induced ultrafast spin current. Quantitative modeling shows that such spin-lattice scattering events occur on similar time scales than the conventional spin conserving electronic scattering (similar to 30 fs). This is significantly faster than optical laser-induced demagnetization. THz conductivity measurements point towards the influence of lattice disorder in amorphous CoFeB as the driving force for enhanced spin-lattice scattering.

  • 2015. D. Backes (et al.). Physical Review Letters 115 (12)

    We report the direct observation of a localized magnetic soliton in a spin-transfer nanocontact using scanning transmission x-ray microscopy. Experiments are conducted on a lithographically defined 150 nm diameter nanocontact to an ultrathin ferromagnetic multilayer with perpendicular magnetic anisotropy. Element-resolved x-ray magnetic circular dichroism images show an abrupt onset of a magnetic soliton excitation localized beneath the nanocontact at a threshold current. However, the amplitude of the excitation ≃25° at the contact center is far less than that predicted (⪅180°), showing that the spin dynamics is not described by existing models.

  • 2015. Stefano Bonetti (et al.). Nature Communications 6

    Spin waves, the collective excitations of spins, can emerge as nonlinear solitons at the nanoscale when excited by an electrical current from a nanocontact. These solitons are expected to have essentially cylindrical symmetry (that is, s-like), but no direct experimental observation exists to confirm this picture. Using a high-sensitivity time-resolved magnetic X-ray microscopy with 50 ps temporal resolution and 35 nm spatial resolution, we are able to create a real-space spin-wave movie and observe the emergence of a localized soliton with a nodal line, that is, with p-like symmetry. Micromagnetic simulations explain the measurements and reveal that the symmetry of the soliton can be controlled by magnetic fields. Our results broaden the understanding of spin-wave dynamics at the nanoscale, with implications for the design of magnetic nanodevices.

  • 2015. R. Kukreja (et al.). Physical Review Letters 115 (9)

    We have used a MHz lock-in x-ray spectromicroscopy technique to directly detect changes in magnetic moment of Cu due to spin injection from an adjacent Co layer. The elemental and chemical specificity of x rays allows us to distinguish two spin current induced effects. We detect the creation of transient magnetic moments of 3×10^{-5}μ_{B} on Cu atoms within the bulk of the 28 nm thick Cu film due to spin accumulation. The moment value is compared to predictions by Mott's two current model. We also observe that the hybridization induced existing magnetic moments at the Cu interface atoms are transiently increased by about 10% or 4×10^{-3}μ_{B} per atom. This reveals the dominance of spin-torque alignment over Joule heat induced disorder of the interfacial Cu moments during current flow.

Visa alla publikationer av Stefano Bonetti vid Stockholms universitet

Senast uppdaterad: 29 maj 2018

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