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  • 1. Adeyev, V.M.
    et al.
    Vasylyev, M.O.
    Pogorelov, Ye.
    Features of auger-investigations of ultrathin periodic metallic film structures2006In: Metallofizika i novejsie tehnologii, ISSN 1024-1809, Vol. 28, no 2, p. 193-200Article in journal (Refereed)
    Abstract [en]

    In the presented work the applicability of Auger Electron Spectroscopy for studying layered metal film structures Fe/(Au, Cu)/Tb on Si substrate with thickness of layers up to 30 Å was shown. It was ascertained that Fe layer is interacting with Si substrate and as a result Fe-silicide is formed. The thickness of buffer layers aimed to protect Fe layer appeared to be insufficient for complete suppression of silicide formation

  • 2. Chung, S.
    et al.
    Mohseni, S. M.
    Sani, S. R.
    Iacocca, E.
    Dumas, R. K.
    Nguyen, T. N. Anh
    Pogoryelov, Ye.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Muduli, P. K.
    Eklund, A.
    Hoefer, M.
    Akerman, J.
    Spin transfer torque generated magnetic droplet solitons (invited)2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 17Article in journal (Refereed)
    Abstract [en]

    We present recent experimental and numerical advancements in the understanding of spin transfer torque generated magnetic droplet solitons. The experimental work focuses on nano-contact spin torque oscillators (NC-STOs) based on orthogonal (pseudo) spin valves where the Co fixed layer has an easy-plane anisotropy, and the [Co/Ni] free layer has a strong perpendicular magnetic anisotropy. The NC-STO resistance and microwave signal generation are measured simultaneously as a function of drive current and applied perpendicular magnetic field. Both exhibit dramatic transitions at a certain current dependent critical field value, where the microwave frequency drops 10 GHz, modulation sidebands appear, and the resistance exhibits a jump, while the magnetoresistance changes sign. We interpret these observations as the nucleation of a magnetic droplet soliton with a large fraction of its magnetization processing with an angle greater than 90 degrees, i.e., around a direction opposite that of the applied field. This interpretation is corroborated by numerical simulations. When the field is further increased, we find that the droplet eventually collapses under the pressure from the Zeeman energy. (C) 2014 AIP Publishing LLC.

  • 3. Dumas, Randy K.
    et al.
    Sani, Sohrab R.
    Mohseni, S. Majid
    Iacocca, Ezio
    Pogoryelov, Yevgen
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Muduli, Pranaba K.
    Chung, Sunjae
    Durrenfeld, Philipp
    Akerman, Johan
    Recent Advances in Nanocontact Spin-Torque Oscillators2014In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, no 6, p. 4100107-Article in journal (Refereed)
    Abstract [en]

    We present a comprehensive review of the most recent advances in nanocontact spin torque oscillators (NC-STOs). NC-STOs are highly tunable, with both applied magnetic field and dc, broadband microwave signal generators. As opposed to the nanopillar geometry, where the lateral cross section of the entire device has been confined to a typically <100 nm diameter, in NC-STOs, it is only the current injection site that has been laterally confined on top of an extended magnetic film stack. Three distinct material combinations will be discussed: 1) a Co/Cu/NiFe pseudospin valve (PSV) where both the Co and NiFe have a dominant in-plane anisotropy; 2) a Co/Cu/[Co/Ni](4) orthogonal PSV where the Co/Ni multilayer has a strong perpendicular anisotropy; and 3) a single NiFe layer with asymmetric non-magnetic Cu leads. We explore the rich and diverse magnetodynamic modes that can be generated in these three distinct sample geometries.

  • 4. Filatov, Alexander
    et al.
    Pogorelov, Alexander
    Pogoryelov, Yevgen
    Negative differential resistance in magnetic tunnel junction systems2014In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 251, no 1, p. 172-177Article in journal (Refereed)
    Abstract [en]

    We study the electrophysical properties of the Fe/MgO/Femagnetic tunnel junctions (MTJ) with impurities. Samplestructures are fabricated on top of fine-crystalline glass–ceramicsubstrates by e-beam evaporation in a relatively low vacuum(~10-4 Torr). The influence of the first magnetic layerfabrication conditions on the degradation of the MTJ isexplained by the interlayer diffusion. Various models ofelectrophysical processes in MTJ on polycrystalline substratesare discussed. The current–voltage (I–V) characteristics of thefabricated structures are found to exhibit a region with negativedifferential resistance, similar to the one in tunneling diodes.We explain this phenomenon by the formation of excitons inthe MgO layer modified by the conductive impurity atoms andtheir diffusion. The obtained results will be useful in thedevelopment of MRAM devices containing MTJs andtunneling diodes.

  • 5. Gomonay, E.
    et al.
    Pogoryelov, Ye.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    External magnetic field influence corrections in RKKY exchange coupling model2005In: INTERMAG Asia 2005: Digest of the IEEE International Magnetics Conference (IEEE Cat. No.05CH37655), 2005, p. 611-12Conference paper (Refereed)
    Abstract [en]

    In the present work a theoretical ground for the influence of external magnetic field on coupling oscillations behaviour is proposed and corresponding modification of Bruno’s formula was made.

  • 6. Gomonay, E.
    et al.
    Pogoryelov, Ye.
    Possible mechanisms of the external magnetic field influence on the exchange coupling2005In: IEEE Transactions on Magnetics, Vol. 41, no 10, p. 2598-2599Article in journal (Refereed)
    Abstract [en]

    Possible mechanisms of the external magnetic field influence on exchange coupling in ultrathin M/N/M film structures are discussed. Itis shown that the most reasonable mechanism is due to variation of the translational motion of spacer electrons in the external magnetic field. In this case in-plane components of the electron momentum should be quantized according to Landau levels. The most drastic effect should be observed in the case when magnetic field is perpendicular to the film plane. Comparison of calculations according to the proposed model with the experimental data is presented, showing very good correlation for the cases of presence and absence of external magnetic field

  • 7. Milstein, K. A.
    et al.
    Pogoryelov, Ye.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Frequency characteristics of optical travelling-wave modulators built on tapered coupler1998In: MMET Conference Proceedings. 1998 International Conference on Mathematical Methods in Electromagnetic Theory. MMET 98 (Cat. No.98EX114), 1998, p. 917-19Conference paper (Refereed)
    Abstract [en]

    The model of the amplitude modulator built on a tapered coupler was investigated and numerically modelled. The connection between the coupling coefficient function and frequency characteristics was found and the possibility of the effective bandwidth widening was demonstrated.

  • 8. Mohseni, S. M.
    et al.
    Sani, S. R.
    Dumas, R. K.
    Persson, J.
    Anh Nguyen, T. N.
    Chung, S.
    Pogoryelov, Ye.
    Muduli, P. K.
    Iacocca, E.
    Eklund, A.
    \AA kerman, J.
    Magnetic droplet solitons in orthogonal nano-contact spin torque oscillators2014In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 435, p. 84-87Article in journal (Refereed)
    Abstract [en]

    We study microwave signal generation as a function of drive current and applied perpendicular magnetic field in nano-contact spin torque oscillators (NC-STOs) based on orthogonal (pseudo) spin valves where the Co fixed layer has strong easy-plane anisotropy, and the [Co/Ni] free layer has a strong perpendicular magnetic anisotropy. The orthogonal NC-STOs exhibit a dramatic transition from the conventional ferromagnetic resonance-like spinwave mode to a magnetic droplet soliton mode. In particular, the field and current dependence of the droplet soliton near threshold are discussed. Near threshold the droplet soliton undergoes complex dynamics that include mode hopping, as evident in the experimental frequency domain and magnetoresistance response.

  • 9. Mohseni, S. M.
    et al.
    Sani, S. R.
    Persson, J.
    Anh Nguyen, T. N.
    Chung, S.
    Pogoryelov, Ye.
    Åkerman, Johan
    High frequency operation of a spin-torque oscillator at low field2011In: physica status solidi (RRL) - Rapid Research Letters, Vol. 5, no 12, p. 432-434Article in journal (Refereed)
  • 10. Mohseni, S. M.
    et al.
    Sani, S. R.
    Persson, J.
    Nguyen, T. N. A.
    Chung, S.
    Pogoryelov, Ye.
    Muduli, P. K.
    Iacocca, E.
    Eklund, A.
    Dumas, R. K.
    Bonetti, S.
    Deac, A.
    Hoefer, M. a.
    Akerman, J.
    Spin Torque-Generated Magnetic Droplet Solitons2013In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 339, no 6125, p. 1295-1298Article in journal (Refereed)
    Abstract [en]

    Dissipative solitons have been reported in a wide range of nonlinear systems, but the observation of their magnetic analog has been experimentally challenging. Using spin transfer torque underneath a nanocontact on a magnetic thin film with perpendicular magnetic anisotropy (PMA), we have observed the generation of dissipative magnetic droplet solitons and report on their rich dynamical properties. Micromagnetic simulations identify a wide range of automodulation frequencies, including droplet oscillatory motion, droplet “spinning,” and droplet “breather” states. The droplet can be controlled by using both current and magnetic fields and is expected to have applications in spintronics, magnonics, and PMA-based domain-wall devices.

  • 11. Muduli, P K
    et al.
    Pogoryelov, Ye
    Consolo, G
    Mancoff, Fred
    Åkerman, Johan
    Modulation of single and double spin torque oscillators2011In: AIP Conf. Proc., Vol. 1347, p. 318-321Article in journal (Refereed)
    Abstract [en]

    We discuss modulation of metallic spin torque oscillators (STOs) based on single and double nano-contacts. The modulation behavior of both types of devices is characterized by equally spaced multiple sidebands, which can be ascribed mostly to a frequency modulation phenomenon. However, quantitative examination reveals that amplitude modulation is also present in both types of devices. We also show the feasibility of modulating the synchronized state of a double nano-contact STO. The synchronized state can be treated as a single oscillator, which is a very promising feature for future applications of STO arrays.

  • 12. Muduli, P K
    et al.
    Pogoryelov, Ye.
    Mancoff, Fred
    Akerman, J.
    Modulation of Individual and Mutually Synchronized Nanocontact-Based Spin Torque Oscillators2011In: IEEE Transactions on Magnetics, Vol. 47, no 6, p. 1575-1579Article in journal (Refereed)
    Abstract [en]

    We study current modulation of spin torque oscillators (STOs) based on single and double nano-contacts. For single nano-contact devices, we show modulation for a carrier frequency of 19-40 GHz and modulation frequencies from 50 MHz to 1 GHz. We show that the behavior of modulation and the asymmetry in the power of the modulation sidebands can be very well modeled, and predicted, using Non-Linear Frequency and Amplitude Modulation (NFAM) calculations based on the free-running STO parameters. Modulation of synchronized double nano-contact STOs is equally well modeled by NFAM theory and demonstrates the feasibility of communication applications based on future arrays of synchronized STOs

  • 13. Muduli, P. K.
    et al.
    Pogoryelov, Ye.
    Zhou, Y.
    Mancoff, Fred
    Åkerman, Johan
    Spin Torque Oscillators and RF currents – Modulation, Locking, and Ringing2011In: Integrated Ferroelectrics, Vol. 125, p. 147-154Article in journal (Refereed)
    Abstract [en]

    We study the interaction between a nano-contact spin torque oscillator (STO) and injected radio-frequency and microwave currents. Modulation of the STO signal is observed over a wide frequency range from 100 MHz to 3.2 GHz. The modulation sidebands agree well with macrospin simulations. When the injected microwave frequency approaches that of the STO, we observe injection locking, frequency pulling/pushing, and intermodulation peaks. While the intermodulation peaks are reasonably well reproduced by macrospin simulations, they do not follow the Adler’s model. We argue that this discrepancy is due to intrinsic ringing effects stemming from the internal dynamics of the STO.

  • 14. Muduli, Pranaba Kishor
    et al.
    Pogoryelov, Yevgen
    Bonetti, Stefano
    Consolo, Giancarlo
    Mancoff, Fred
    Åkerman, Johan
    Nonlinear frequency and amplitude modulation of a nanocontact-based spin-torque oscillator2010In: Physical Review B, Vol. 81, no 14, p. 140408(R)-Article in journal (Refereed)
    Abstract [en]

    We study the current-controlled modulation of a nanocontact spin-torque oscillator. Three principally dif-ferent cases of frequency nonlinearity (d2f/dIdc2 being zero, positive, and negative) are investigated. Standardnonlinear frequency-modulation theory is able to accurately describe the frequency shifts during modulation. However, the power of the modulated sidebands only agrees with calculations based on a recent theory of combined nonlinear frequency and amplitude modulation.

  • 15. Persson, Johan
    et al.
    Sani, Sohrab Redjai
    Bonetti, Stefano
    Magnusson, Fredrik
    Pogoryelov, Yevgen
    Mohseni, Seyed Majid
    Gunnarsson, Sten
    Norling, Martin
    Stoij, Christer
    Akerman, Johan
    Spin-Torque Oscillator in an Electromagnet Package2012In: IEEE Transactions on Magnetics, Vol. 48, no 11, p. 4378-4381Article in journal (Refereed)
    Abstract [en]

    Spin-torque oscillators (STO) hold promise for multi-octave frequency operation at very high frequencies and modulation speeds. STO operation is typically demonstrated using large electromagnets and probe stations, and has so far not been packaged with a portable form factor. For STOs to be utilized in real applications, a smaller packaging solution is needed. We integrate STOs with packages originally developed for YIG oscillators, modified to incorporate permanent magnets and to achieve a compact portable oscillator based on the STO.

  • 16. Phuoc, N. N.
    et al.
    Pogoryelov, Ye.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Suzuki, T.
    Hybrid exchange bias in (FePt-FeMn) N multilayers2005In: INTERMAG Asia 2005: Digest of the IEEE International Magnetics Conference (IEEE Cat. No.05CH37655), 2005, p. 2045-6Conference paper (Refereed)
    Abstract [en]

    The present work reports about the study of a hybrid type of longitudinal and perpendicular exchange bias in [FePt/FeMn] N (N=1~10) multilayers. Ion beam sputtering technique was used to prepare the samples. X-ray diffraction technique and vibrating sample magnetometer are used to characterize the structural and magnetic properties of the samples, respectively. The dependence of in-plane and out-of-plane exchange bias on temperature and FePt thickness is investigated showing a similar dependence for both the cases except on their dependence on the cooling field.

  • 17. Pogorelov, A.
    et al.
    Pogoryelov, Ye.
    Zhuravlev, A.
    Optimization of data storage density and data media quality monitoring in film storage thermal recording devices2002In: Journal of Magnetism and Magnetic Materials, Vol. 249, no 3, p. 428-430Article in journal (Refereed)
    Abstract [en]

    The new method for express analysis of the film’s thermophysical characteristics is presented. On the basis of thismethod an original approach to optimization of the data recording on CD is proposed. The method has high sensitivity and allows using standard devices for CD quality monitoring and also for film or other coating adhesion to the substrate.

  • 18. Pogorelov, Alexander
    et al.
    Zhuravlev, Anatoly
    Pogoryelov, Yevgen
    Brik, Viktor
    Rapid method for determination of thermal-physical parameters of new materials, films and coatings2001In: Metallofizika i Noveishie Tekhnologii, Vol. 23, p. 194-198Article in journal (Refereed)
  • 19.
    Pogoryelov, E.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Peculiarities of the Hall Effect Aplicationfor Magnetic Nanostructures Studies2008In: Metallofizika i novejsie tehnologii, ISSN 1024-1809, Vol. 30, p. 35-46Article in journal (Refereed)
    Abstract [en]

    The present work is discussing the peculiarities of application of both traditional anomalous and planar Hall effects as well as originally developed spin-Hall effect based method for studies of magnetic nanostructures. Along with the possibility to study magnetic properties of single isolated magnetic nanoparticles the Hall-effect based techniques may be also used for working the process of their fabrication. With the help of spin-Hall effect based method the influence of external magnetic field on the behavior of exchange coupling in ultrathin tri-layer MINIM film structure was discovered. Coefficients of spin-polarization in the structures investigated at room temperatures were determined. It was shown that Hall effect based techniques are most preferable for studies of magnetic nanostructures due to their high sensitivity for small amount of material.

  • 20. Pogoryelov, Ye.
    External Magnetic Field Influence on Exchange Coupling Oscillations in Ultrathin Fe/Au/Tb Film Structures2004In: J. Magnetics, Vol. 9, no 4, p. 97-100Article in journal (Refereed)
    Abstract [en]

    In the present work exchange coupling between ultrathin Fe (8Å) and Tb (12Å) layers separated by Au spacer of varied thickness (3~20Å) was studied. Anomalous Hall effect measurements showed weakly damped oscillat- ing dependence of the Hall conductivity as a function of Au spacer thickness. Disagreement of the observed damping with the RKKY model of interlayer exchange coupling was explained by the influence of external magnetic field on the behaviour of exchange coupling oscillations. It was confirmed by Hall-like effect measure- ments at zero applied magnetic field and also illustrated by corresponding estimations.

  • 21. Pogoryelov, Ye.
    Preparation and characterization of ultrathin films and film coatings for microelectronics2004Conference paper (Refereed)
  • 22. Pogoryelov, Ye.
    Simulation of exchange coupling in three-layered film structures Fe/Au/Tb2003In: Metallofizika i Noveishie Tekhnologii, Vol. 25, no 1, p. 47-51Article in journal (Refereed)
  • 23. Pogoryelov, Ye.
    et al.
    Muduli, P. K.
    Akerman, J.
    Combined Wide-Narrow Double Modulation of Spin-Torque Oscillators for Improved Linewidth During Communication2012In: IEEE Transactions on Magnetics, Vol. 48, no 11, p. 4077-4080Article in journal (Refereed)
    Abstract [en]

    Spin-torque oscillators (STOs) offer the advantage of high modulation rates. However the existence of regions with high-frequency nonlinearity, accompanied by increased signal linewidth, limits both the usable STO frequency range and the minimum frequency of modulation. On the other hand, use of a large modulation frequency increases the frequency modulation (FM) bandwidth. In order to overcome these problems, we propose to simultaneously modulate the STO with two signals having different frequencies. We use a high-frequency, “wide” $(f_{rm W}=500 {rm MHz})$ , modulation signal to improve the STO linewidth. At the same time we use a low-frequency, “narrow” $(f_{rm N}=40 {rm MHz})$, modulation signal to show successful narrow bandwidth modulation of the improved STO signal. The proposed method of combined wide-narrow double modulation can significantly improve the usable operating frequency range of the STOs for communication applications.

  • 24. Pogoryelov, Ye
    et al.
    Muduli, P K
    Bonetti, S
    Iacocca, E
    Mancoff, Fred
    Åkerman, Johan
    Frequency modulation of spin torque oscillator pairs2011In: Applied Physics Letters, Vol. 98, no 19, p. 192501-Article in journal (Refereed)
    Abstract [en]

    The current controlled modulation of nanocontact based spin torque oscillator (STO) pairs is studied in both the synchronized and nonsynchronized states. The synchronized state shows a well behaved modulation and demonstrates robust mutual locking even under strong modulation. The power distribution of the modulation sidebands can be quantitatively described by assuming a single oscillator model. However, in the nonsynchronized state, the modulation sidebands are not well described by the model, indicating interactions between the two individual nanocontact STOs. These findings are promising for potential applications requiring the modulation of large synchronized STO arrays.

  • 25. Pogoryelov, Ye.
    et al.
    Muduli, P. K.
    Bonetti, S.
    Mancoff, Fred
    Åkerman, Johan
    Spin-torque oscillator linewidth narrowing under current modulation2011In: Applied Physics Letters, Vol. 98, no 19, p. 192506-Article in journal (Refereed)
    Abstract [en]

    We study the behavior of the linewidth of a nanocontact based spin torque oscillator (STO) under application of a radio frequency (100 MHz) modulating current. We achieve a significant (up to 85%) reduction in the STO linewidth when it is modulated across a region of high nonlinearity. The mechanism responsible for the linewidth reduction is the nonlinear frequency shift under the influence of current modulation, which reduces the nonlinear amplification of the linewidth. The reduction in the linewidth during modulation can be quantitatively calculated from the free-running behavior of the STO.

  • 26. Pogoryelov, Ye.
    et al.
    Åkerman, J.
    Manifestation of spin-Hall effect in multilayered M/N/M film structures2010In: J. Phys.: Conf. Ser., Vol. 200, no 5, p. 052023-Article in journal (Refereed)
    Abstract [en]

    In the present work spin-Hall effect was for the first time experimentally utilized at room temperatures for studies of interlayer exchange coupling in ultrathin (3-40Å) M/N/M film structures at zero applied external magnetic field. Application of special technique allowed to discover the possible influence of external magnetic field on the behavior of exchange coupling oscillations. Obtained results are well explained if to take into account in the RKKY model the probable influence of magnetic field on the spin-dependent reflection coefficients of spin-polarized conduction electrons from magnetic interfaces.

  • 27. Pogoryelov, Yevgen A.
    et al.
    Adeev, V.M.
    Bondar, V.I.
    Influence of Si substrate and interface quality on exchange interactions in ultrathin Fe/NM/Tb film structure2005In: Functional Materials, ISSN 1027-5495, Vol. 12, no 1, p. 120-123Article in journal (Refereed)
  • 28. Pogoryelov, Yevgen
    et al.
    Podyalovski, D.I.
    Exchange coupling peculiarities in ultrathin Fe/Cu/Tb film structures on Si substrates2004In: Functional Materials, ISSN 1027-5495, Vol. 11, no 3, p. 560-562Article in journal (Refereed)
  • 29. Pogoryelov, Yevgen
    et al.
    Suzuki, Takao
    Fabrication of Alloy FeCoPt Particles by IBICVD and Their Characterization2007In: IEEE Transactions on Magnetics, Vol. 43, no 2, p. 888-890Article in journal (Refereed)
    Abstract [en]

    Ion beam induced chemical vapor deposition (IBICVD) has been for the first time successfully applied for direct patterned depositionof ternary alloy FeCoPt particles. Magnetic force microscopy (MFM) studies revealed existence of the magnetic ring domain structure in annealed particles. Fabricated FeCoPt particles exhibit soft ferromagnetic properties. It was found that coercivity of the annealed particles increases almost twice that may suggest the improvement of their ordering. The successful fabrication of ternary alloy particles may lead to the potential application of IBICVD for novel composite nanoparticles.

  • 30. Puliafito, Vito
    et al.
    Pogoryelov, Yevgen
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Azzerboni, Bruno
    Akerman, Johan
    Finocchio, Giovanni
    Hysteretic Synchronization in Spin-Torque Nanocontact Oscillators: A Micromagnetic Study2014In: IEEE transactions on nanotechnology, ISSN 1536-125X, E-ISSN 1941-0085, Vol. 13, no 3, p. 532-536Article in journal (Refereed)
    Abstract [en]

    Several experiments report the presence of finite jumps in the properties of spin-torque oscillators at room temperature, such as oscillation frequency and power as functions of current or field. On the basis of micromagnetic simulations, this paper links those experimental discontinuities to the changes in the curve slope numerically observed in the absence of thermal effects. Our numerical results show the key ingredient triggering this behavior is the presence of abrupt changes in the oscillation axis of the magnetization precession. We also predict that by fixing the bias point of the oscillator near those critical regions, it is possible to observe hysteretic synchronization. This result should be a key point in the design of nanoscale on-chip phase-locked loop receivers with improved sensitivity.

  • 31. Sani, S.
    et al.
    Persson, J.
    Mohseni, S.M.
    Pogoryelov, Ye.
    Muduli, P.K.
    Eklund, A.
    Malm, G.
    Käll, M.
    Dmitriev, A.
    Åkerman, J.
    Mutually synchronized bottom-up multi-nanocontact spin–torque oscillators2013In: Nature Communications, Vol. 4Article in journal (Refereed)
    Abstract [en]

    Spin–torque oscillators offer a unique combination of nanosize, ultrafast modulation rates and ultrawide band signal generation from 100MHz to close to 100 GHz. However, their low output power and large phase noise still limit their applicability to fundamental studies of spin-transfer torque and magnetodynamic phenomena. A possible solution to both problems is the spin-wave-mediated mutual synchronization of multiple spin–torque oscillators through a shared excited ferromagnetic layer. To date, synchronization of high-frequency spin–torque oscillators has only been achieved for two nanocontacts. As fabrication using expensive top–down lithography processes is not readily available to many groups, attempts to syn- chronize a large number of nanocontacts have been all but abandoned. Here we present an alternative, simple and cost-effective bottom-up method to realize large ensembles of synchronized nanocontact spin–torque oscillators. We demonstrate mutual synchronization of three high-frequency nanocontact spin–torque oscillators and pairwise synchronization in devices with four and five nanocontacts.

  • 32. Shypil, E.
    et al.
    Pogorilyy, A.
    Pogoryelov, Ye.
    Kim, T.H.
    Berera, G.
    Moodera, J.
    Magnetic interactions in MBE grown Fe/x Au/Tb trilayers2002In: Journal of Magnetism and Magnetic Materials, Vol. 242-245, p. 532-534Article in journal (Refereed)
    Abstract [en]

    Indirect exchange coupling between Fe and Tb layers showed oscillatory behaviour through Au layer as a function ofits thickness. Trilayers, prepared in the MBE system, were characterized with different experimental tools. Results are analysed to reconstruct the dynamics of Fe and Tb magnetic moments. For the first time, the change of sign in magnetic interaction is shown for Fe/Au/Tb system.

  • 33. Shypil, E. V.
    et al.
    Pogorily, A. M.
    Podyalovski, D. I.
    Pogoryelov, Y. A.
    Interlayer coupling in Tb/Fe bilayers and Tb/Au/Fe trilayers with sharp or rough interface2001In: Low Temperature Physics, Vol. 27, no 8, p. 650-654Article in journal (Refereed)
    Abstract [en]

    Bilayer films Fe/Tb (Tb on Fe) having sharp and Tb/Fe (Fe on Tb) having rough interface were prepared by molecular beam epitaxy to study interlayer magnetic coupling. Magnetic properties of these bilayers were characterized ex situ using ferromagnetic resonance (FMR), polar magneto-optical Kerr effect and SQUID magnetometer. The resulting perpendicular magnetic anisotropy (PMA) is discussed as an effect of interlayer magnetic coupling. PMA was observed in rough as well as in sharp interfaces and the anisotropy energies were estimated. When a monolayer of Au was interposed at the interface of both kinds, PMA was observed to disappear and the overall magnetic moment increased. It was also shown that in ultrathin films demagnetization factor depends on the substrate roughness and should be considered in the FMR data.

  • 34. Shypil, E.V.
    et al.
    Pogorilyy, A.M.
    Pogoryelov, Ye.O.
    Polar magneto-optical Kerr effect studies of interlayer exchange coupling in Fe/Tb bilayers and Fe/Au/Tb trilayers2002In: Semiconductor Physics, Quantum Electronics & Optoelectronics, Vol. 5, no 2, p. 212-216Article in journal (Refereed)
    Abstract [en]

    Interlayer exchange coupling was studied. The investigations were carried out on bilayer (Fe/Tb) and trilayer (Fe/Au/Tb) ultrathin film structures. The films on silica substrate were prepared by electron-beam evaporation in an MBE system with a background pressure of (1 ·5) · 10-10 Torr and maintaining a pressure of (1 · 3) · 10-9 Torr during the film growth. To investigate these film structures polar magneto-optical Kerr effect was used. In bilayers the perpendicular magnetic anisotropy was observed. When a monolayer of Au was interposed at the interface, was observed to disappear. This is because of breaking the short-range interaction between Fe and Tb layers. Instead a long-range indirect exchange via nonmagnetic Au interlayer appears. The increase of Au interlayer thickness (3 · 35 Å) resulted in the oscillations of the Kerr angle. Analogous oscillations are distinctive to the RKKY model of interlayer exchange coupling.

  • 35. Suzuki, T.
    et al.
    Pogoryelov, Ye.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Spin-dependent effects in ultrathin trilayer M/N/M film structures2005In: INTERMAG Asia 2005: Digest of the IEEE International Magnetics Conference (IEEE Cat. No.05CH37655), 2005, p. 1211-12Conference paper (Refereed)
    Abstract [en]

    The peculiarities of spin-dependent effects when applied to the interlayer exchange coupling in an M/N/M trilayer film structure was investigated. It was found that by changing the nonmagnetic spacer thickness in the trilayer film, it is possible to change the spin polarisation coefficient.

  • 36.
    Wei, Yajun
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Akansel, Serkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Thersleff, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Harward, Ian
    Brucas, Rimantas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ranjbar, Mojtaba
    Jana, Somnath
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Lansåker, Pia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Pogoryelov, Yevgen
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Dumas, Randy K.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Akerman, Johan
    Celinski, Zbigniew
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Exponentially decaying magnetic coupling in sputtered thin film FeNi/Cu/FeCo trilayers2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 4, article id 042405Article in journal (Refereed)
    Abstract [en]

    Magnetic coupling in trilayer films of FeNi/Cu/FeCo deposited on Si/SiO2 substrates have been studied. While the thicknesses of the FeNi and FeCo layers were kept constant at 100 angstrom, the thickness of the Cu spacer was varied from 5 to 50 angstrom. Both hysteresis loop and ferromagnetic resonance results indicate that all films are ferromagnetically coupled. Micromagnetic simulations well reproduce the ferromagnetic resonance mode positions measured by experiments, enabling the extraction of the coupling constants. Films with a thin Cu spacer are found to be strongly coupled, with an effective coupling constant of 3 erg/cm(2) for the sample with a 5 angstrom Cu spacer. The strong coupling strength is qualitatively understood within the framework of a combined effect of Ruderman-Kittel-Kasuya-Yosida and pinhole coupling, which is evidenced by transmission electron microscopy analysis. The magnetic coupling constant surprisingly decreases exponentially with increasing Cu spacer thickness, without showing an oscillatory thickness dependence. This is partially connected to the substantial interfacial roughness that washes away the oscillation. The results have implications on the design of multilayers for spintronic applications.

  • 37.
    Wei, Yajun
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Jana, Somnath
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Brucas, Rimantas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Pogoryelov, Yevgen
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Ranjbar, Mojtaba
    Arena, Dario A
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Dumas, Randy K
    Warnicke, Peter
    Johan, A
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Magnetic coupling in asymmetric FeCoV / Ru / FeNi trilayers2014In: Journal of Applied Physics, Vol. 115, no 17, p. 17D129-Article in journal (Refereed)
    Abstract [en]

    We have investigated the magnetic anisotropy and interlayer coupling in trilayer films of permendur(100 \AA)/Ru/permalloy(100 \AA), with the thickness of the Ru spacer varying from 0 to 200 \AA. While the permendur/permalloy sample exhibits a small in-plane uniaxial magnetic anisotropy with Hu = 27 Oe, all trilayers are magnetically isotropic in-plane. Results from hysteresis loop and ferromagnetic resonance measurements were fitted to a micromagnetic model, with the results indicating that all the films are ferromagnetically coupled except the one with 10 \AA Ru spacer, which shows antiferromagnetic coupling. The trilayers with Ru spacer layer thickness larger than 20 \AA exhibit only very weak ferromagnetic coupling.

1 - 37 of 37
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