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  • 1.
    Bonetti, Stefano
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Muduli, Pranaba
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Mancoff, Fred
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Spin torque oscillator frequency versus magnetic field angle: The prospect of operation beyond 65 GHz2009Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, nr 10Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the impact of the magnetic field angle on the oscillation frequency of a nanocontact spin torque oscillator (STO) in magnetic fields up to 2.1 T. A model based on a single nonlinear, nonpropagating spin wave mode is found to explain the experimental data. We observe oscillation frequencies as high as 46 GHz in high magnetic fields applied normal to the film plane, and we are able to extrapolate the maximum expected operating frequency to beyond 65 GHz for in-plane magnetic fields. The STO signal remains surprisingly strong at these conditions, which opens up for possible millimeter-wave applications.

  • 2.
    Bonetti, Stefano
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Tiberkevich, Vasil
    Consolo, Giancarlo
    Finocchio, Giovanni
    Muduli, Pranaba
    Mancoff, Fred
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Experimental evidence of self-localized and propagating spin wave modes in obliquely magnetized current-driven magnetic nanocontacts2010Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, nr 21, s. 217204-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Through detailed experimental studies of the angular dependence of spin wave excitations in nanocontact-based spin-torque oscillators, we demonstrate that two distinct spin wave modes can be excited, with different frequency, threshold currents, and frequency tunability. Using analytical theory and micromagnetic simulations we identify one mode as an exchange-dominated propagating spin wave, and the other as a self-localized nonlinear spin wave bullet. Wavelet-based analysis of the simulations indicates that the apparent simultaneous excitation of both modes results from rapid mode hopping induced by the Oersted field.

  • 3.
    Muduli, Pranaba
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Friedland, K. -J
    Herfort, J.
    Schoenherr, H. -P
    Ploog, K. H.
    Composition dependent properties of Fe3Si films grown on GaAs(113)A substrates2009Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 105, nr 7, s. 07B104-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Structural, electrical, and magnetic properties of Fe3Si/GaAs(113)A hybrid structures are studied, dependent on the layer composition varying from 15 to 26 at. % Si. The presence of superlattice reflections in x-ray diffraction and lower resistivity confirms the long-range atomic ordering in the stoichiometric Fe3Si films, reflecting the D0(3) crystal structure. The observed atomic ordering is also found to influence the sign and magnitude of the antisymmetric component of the planar Hall effect observed in this orientation. However a finite disorder is observed even in nearly stoichiometric samples.

  • 4. Muduli, Pranaba
    et al.
    Herfort, J.
    Schönherr, H. -P
    Ploog, K. H.
    Strong dependence of the magnetic anisotropy on the growth temperature of Fe3+xSi1-x (x=0.34) films on GaAs(113)A substrates2009Inngår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 321, nr 20, s. 3488-3492Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A strong dependence of the magnetic anisotropy on the growth temperature of Fe3+xSi1-x Heusler alloy films on GaAs(113)A substrates is reported for a composition of 17.5 at:% Si (x = 0.34). This composition of Fe-Si alloy lies within the stable phase of the technologically promising Heusler alloy Fe3Si. The layers grown at the optimized growth temperature of 250 degrees C exhibit the expected four-fold magnetic anisotropy, which arises from the magnetocrystalline anisotropy and the large demagnetization energy, similar to Fe films. However, an unexpected strong uniaxial magnetic anisotropy is found for samples grown at 200 and 400 degrees C with the easy axes along < 33 (2) over bar > and <(1) over bar 10 >, respectively. The uniaxial magnetic anisotropy of these samples are shown to be related to the inferior interface quality.

  • 5.
    Muduli, Pranaba K.
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Herfort, J.
    Schoenherr, H. -P
    Ploog, K. H.
    Spin wave excitations in Fe films grown on GaAs(113)A substrates2008Inngår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 320, nr 21, s. 2835-2838Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The spin wave excitation and its size effect has been studied in Al- capped Fe. lms grown on lowsymmetry GaAs( 113) A substrates. The temperature dependence of saturation magnetization follows an effective Bloch's law as long as magnetization remains larger than about 70% of its saturation value. A signi. cant increase of the spin wave parameter B is found in Al- capped ultrathin Fe. lms grown on GaAs( 113) A compared to bulk Fe, Fe. lms on GaAs( 0 01) and other systems. This is explained as a result of the reduction in uniaxial magnetic anisotropy observed in this orientation for the same thickness range. However, this observed uniaxial magnetic anisotropy is found to be a likely reason for stabilizing the ferromagnetism.

  • 6.
    Muduli, Pranaba
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Pogoryelov, Ye.
    Mancoff, F.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Modulation of Individual and Mutually Synchronized Nanocontact-Based Spin Torque Oscillators2011Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 47, nr 6, s. 1575-1579Artikkel i tidsskrift (Fagfellevurdert)
    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 nonlinear 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 arrays of synchronized STOs.

  • 7.
    Muduli, Pranaba
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Pogoryelov, Yevgen
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Bonetti, Stefano
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Consolo, G.
    Mancoff, Fred
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Nonlinear frequency and amplitude modulation of a nanocontact-based spin-torque oscillator2010Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, nr 14Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the current-controlled modulation of a nanocontact spin-torque oscillator. Three principally different cases of frequency nonlinearity (d(2)f/dI(dc)(2) being zero, positive, and negative) are investigated. Standard nonlinear 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.

  • 8.
    Muduli, Pranaba
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Pogoryelov, Yevgen
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Consolo, Giancarlo
    University of Messina.
    Mancoff, Fred
    Everspin Technologies Inc.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Materialfysik, MF.
    Modulation of single and double spin torque oscillators2010Inngår i: INTERNATIONAL CONFERENCE ON MAGNETIC MATERIALS (ICMM-2010), 2010, s. 318-321Konferansepaper (Fagfellevurdert)
    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.

  • 9.
    Muduli, Pranaba
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Rice, W. C.
    He, L.
    Collins, B. A.
    Chu, Y. S.
    Tsui, F.
    Study of magnetic anisotropy and magnetization reversal using the quadratic magnetooptical effect in epitaxial CoxMnyGez(111) films2009Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 21, nr 29, s. 296005-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetic anisotropy, magnetization reversal and the magnetooptic Kerr effect in CoxMnyGez have been studied over a range of compositions between 0 and 50 at.% of Ge and between 1 and 3 in the Co to Mn atomic ratio, including the Heusler alloy Co2MnGe. A strong quadratic magnetooptic Kerr effect has been observed within a narrow region of composition centered around the Co to Mn atomic ratio of 2, which has been used to probe and quantify the magnetic anisotropy and magnetization reversal of the system. The anisotropy is sixfold with a weak uniaxial component, and it exhibits sensitive dependence on composition, especially on the atomic ratio between Co and Mn. The magnetization reversal process is consistent with the single-domain Stoner-Wohlfarth model.

  • 10.
    Zha, Chaolin
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Muduli, Pranaba
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Nogues, Josep
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Exchange-bias-like effect in L1(0) (111) FePt based pseudo spin valves2010Inngår i: INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) / [ed] Goll, G; Lohneysen, HV; Loidl, A; Pruschke, T; Richter, M; Schultz, L; Surgers, C; Wosnitza, J, BRISTOL: IOP PUBLISHING LTD, DIRAC HOUSE , 2010, Vol. 200, s. UNSP 072110-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The coupling between hard FePt/CoFe and soft CoFe/NiFe layers through a Cu spacer has been studied in L1(0) (111) FePt(20)/CoFe(1.5)/Cu(3.5or4.5)/CoFe(2)/NiFe(3) (in nm) pseudo spin valves. The soft layer hysteresis loops exhibit clear shifts in the field axis (exchange bias-like) and a marked coercivity enhancement. The thickness of the Cu layer or the interface roughness influence the exchange bias properties of the systems. This interlayer coupling arises from the competition between dipolar and RKKY interactions between the layers.

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