| 1. |
- Chowdhury, N., et al.
(author)
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Kagome Magnets: The Emerging Materials for Spintronic Memories
- 2023
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In: Proceedings of the National Academy of Sciences India Section a-Physical Sciences. - 0369-8203. ; 93, s. 477-495
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Research review (peer-reviewed)abstract
- Recent developments in the field of topological quantum materials have stimulated the search for materials that could serve as the building blocks for next-generation memory applications. Due to their intriguing topological properties, such as flat bands, Dirac nodes, and Weyl points, kagome magnets are anticipated to be the leading materials for this application. In this mini review, we discuss some of the recent advancements in binary kagome magnets, both ferromagnetic and anti-ferromagnetic, for use as emerging memory devices. First, we discuss ferromagnetic kagome magnets, specifically Fe3Sn2, and then we discuss non-collinear antiferromagnetic kagome magnets, Mn3Sn and Mn3Ir. Finally, we discuss collinear antiferromagnetic kagome magnet, FeSn. In each of the aforementioned sections, we begin with a discussion of their topological, structural, and magnetic properties, followed by application-specific studies such as spin-orbit torques (SOT). In the final section, we discuss the current state of kagome magnets for efficient, faster, denser, and reliable memory technologies with focus on the SOT switching and observation/manipulation of skyrmions.
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| 2. |
- Kumar, Akash, et al.
(author)
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Interfacial Origin of Unconventional Spin-Orbit Torque in Py/r-IrMn3
- 2023
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In: Advanced Quantum Technologies. - 2511-9044. ; 6:7
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Journal article (peer-reviewed)abstract
- Angle-resolved spin-torque ferromagnetic resonance measurements are carried out in heterostructures consisting of Py (Ni81Fe19) and a noncollinear antiferromagnetic quantum material r-IrMn3. The structural characterization reveals that r-IrMn3 is polycrystalline in nature. A large exchange bias of 158 Oe is found in Py/r-IrMn3 at room temperature, while r-IrMn3/Py and Py/Cu/r-IrMn3 exhibit no exchange bias. Regardless of the exchange bias and stacking sequence, a substantial unconventional out-of-plane anti-damping torque is observed when r-IrMn3 is in direct contact with Py. The magnitude of the out-of-plane spin-orbit torque efficiency is found to be twice as large as the in-plane spin-orbit torque efficiency. The unconventional spin-orbit torque vanishes when a Cu spacer is introduced between Py and r-IrMn3, indicating that the unconventional spin-orbit torque in this system originates at the interface. These findings are important for realizing efficient antiferromagnet-based spintronic devices via interfacial engineering.
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| 3. |
- Sharma, R., et al.
(author)
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Modulation Rate Study in a Spin-Torque Oscillator-Based Wireless Communication System
- 2015
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In: IEEE transactions on magnetics. - : IEEE Press. - 0018-9464 .- 1941-0069. ; 51:11
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Journal article (peer-reviewed)abstract
- We study a wireless communication system based on a magnetic tunnel junction spin-torque nano-oscillator (STNO) by employing amplitude-shift-keying modulation. By varying the pulse modulation frequency (f(m)) from 1 kHz to 2 MHz and distance (D) between the antenna from 25 to 150 cm, we show a maximum data rate of 6 Mb/s (at D = 25 cm and fm = 1 MHz), a limit imposed by our setup and noise generated by the STNO itself. We also report the average amplitude noise (S-delta a) and average white frequency noise (S-wh) of the wireless communication system and discuss their dependence on the distance between the antennas.
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| 4. |
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| 5. |
- Bangar, H., et al.
(author)
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Large Spin Hall Conductivity in Epitaxial Thin Films of Kagome Antiferromagnet Mn3Sn at Room Temperature
- 2022
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In: Advanced Quantum Technologies. - : Wiley. - 2511-9044. ; 6:1
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Journal article (peer-reviewed)abstract
- Mn3Sn is a non-collinear antiferromagnetic quantum material that exhibits a magnetic Weyl semimetallic state and has great potential for efficient memory devices. High-quality epitaxial c-plane Mn3Sn thin films have been grown on a sapphire substrate using a Ru seed layer. Using spin pumping induced inverse spin Hall effect measurements on c-plane epitaxial Mn3Sn/Ni80Fe20, spin-diffusion length (lambda(Mn3Sn)), and spin Hall conductivity (sigma(SH)) of Mn3Sn thin films are measured: lambda(Mn3Sn) = 0.42 +/- 0.04 nm and sigma(SH) = -702 h/e Omega(-1)cm(-1). While lambda(Mn3Sn) is consistent with earlier studies, sigma(SH) is an order of magnitude higher and of the opposite sign. The behavior is explained on the basis of excess Mn, which shifts the Fermi level in these films, leading to the observed behavior. These findings demonstrate a technique for engineering sigma(SH) of Mn3Sn films by employing Mn composition for functional spintronic devices.
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| 6. |
- Bangar, H., et al.
(author)
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Large Spin-To-Charge Conversion at the Two-Dimensional Interface of Transition-Metal Dichalcogenides and Permalloy
- 2022
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In: ACS Applied Materials & Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 14:36, s. 41598-41604
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Journal article (peer-reviewed)abstract
- Spin-to-charge conversion is an essential requirement for the implementation of spintronic devices. Recently, monolayers (MLs) of semiconducting transition-metal dichalcogenides (TMDs) have attracted considerable interest for spin-to-charge conversion due to their high spin-orbit coupling and lack of inversion symmetry in their crystal structure. However, reports of direct measurement of spin-to-charge conversion at TMD-based interfaces are very much limited. Here, we report on the room-temperature observation of a large spin-to-charge conversion arising from the interface of Ni80Fe20 (Py) and four distinct large-area (similar to 5 x 2 mm(2)) ML TMDs, namely, MoS2, MoSe2, WS2, and WSe2. We show that both spin mixing conductance and the Rashba efficiency parameter (lambda(IREE)) scale with the spin-orbit coupling strength of the ML TMD layers. The lambda(IREE) parameter is found to range between -0.54 and -0.76 nm for the four ML TMDs, demonstrating a large spin-to-charge conversion. Our findings reveal that the TMD/ferromagnet interface can be used for efficient generation and detection of spin current, opening new opportunities for novel spintronic devices.
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| 7. |
- Muduli, Pranaba, et al.
(author)
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Composition dependent properties of Fe3Si films grown on GaAs(113)A substrates
- 2009
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 105:7, s. 07B104-
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Journal article (peer-reviewed)abstract
- 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.
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| 8. |
- Muduli, Pranaba K., et al.
(author)
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Spin wave excitations in Fe films grown on GaAs(113)A substrates
- 2008
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In: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 320:21, s. 2835-2838
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Journal article (peer-reviewed)abstract
- 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.
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| 9. |
- Tiwari, D., et al.
(author)
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Antidamping spin-orbit torques in epitaxial-Py(100)/beta-Ta
- 2017
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 111:23
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Journal article (peer-reviewed)abstract
- We perform spin torque ferromagnetic resonance measurements on the Si(100)/TiN(100)/epi-Py(100)/beta-Ta system. We demonstrate current induced modulation of the Gilbert damping constant, which is about 30% for a current density of 6.25 x 10(9) A/m(2). We show that the observed modulation of the Gilbert damping constant cannot be explained by spin transfer torques arising from the spin Hall effect of the beta-Ta layer. An additional mechanism such as antidamping spinorbit torque resulting from the interface or the crystalline structure of Py thin films needs to be considered. Published by AIP Publishing.
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| 10. |
- Chen, Tingsu, et al.
(author)
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Spin-Torque and Spin-Hall Nano-Oscillators
- 2016
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In: Proceedings of the IEEE. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9219 .- 1558-2256. ; 104:10, s. 1919-1945
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Journal article (peer-reviewed)abstract
- This paper reviews the state of the art in spin-torque and spin-Hall-effect-driven nano-oscillators. After a brief introduction to the underlying physics, the authors discuss different implementations of these oscillators, their functional properties in terms of frequency range, output power, phase noise, and modulation rates, and their inherent propensity for mutual synchronization. Finally, the potential for these oscillators in a wide range of applications, from microwave signal sources and detectors to neuromorphic computation elements, is discussed together with the specific electronic circuitry that has so far been designed to harness this potential.
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| 11. |
- Heinonen, O. G., et al.
(author)
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Decoherence, Mode Hopping, and Mode Coupling in Spin Torque Oscillators
- 2013
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In: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 49:7, s. 4398-4404
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Journal article (peer-reviewed)abstract
- Spin torque oscillators (STOs) often exhibit multiple modes, leading to complex behavior. One example is mode hopping between different eigenmodes of a magnetic tunnel junction (MTJ) STO. This mode hopping is a strong function of current and angle between the magnetization in the free and fixed layers, and away from anti-parallel configuration, mode hopping can be the dominant decoherence process. Another example is the linewidth of a nanocontact STO that can be a complex non-monotonic function of temperature in regions where two or more modes are excited by the oscillators. These phenomena require a generalization of the single-mode nonlinear STO theory to include mode coupling. We derive equations describing the slow time evolution of the coupled system and show they describe a dynamically driven system, similar to other systems that exhibit mode hopping in the presence of thermal fluctuations. In our description, mode coupling also leads to additional coupling between power and phase fluctuations, which can in certain limited cases lead to longer relaxation times for power fluctuations, and consequently to larger linewidths through the nonlinear frequency shift.
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| 12. |
- Husain, Sajid, et al.
(author)
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Observation of Skyrmions at Room Temperature in Co2FeAl Heusler Alloy Ultrathin Film Heterostructures
- 2019
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
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Journal article (peer-reviewed)abstract
- Magnetic skyrmions are topological spin-textures having immense potential for energy efficient spintronic devices. Here, we report the observation of stable skyrmions in unpatterned Ta/Co2FeAl(CFA)/MgO thin film heterostructures at room temperature in remnant state employing magnetic force microscopy. It is shown that these skyrmions consisting of ultrathin ferromagnetic CFA Heusler alloy result from strong interfacial Dzyaloshinskii-Moriya interaction (i-DMI) as evidenced by Brillouin light scattering measurements, in agreement with the results of micromagnetic simulations. We also emphasize on room temperature observation of multiple skyrmions which can be stabilized for suitable combinations of CFA layer thickness, perpendicular magnetic anisotropy, and i-DMI. These results provide a significant step towards designing of room temperature spintronic devices based on skyrmions in full Heusler alloy based thin films.
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| 13. |
- Muduli, P. K., et al.
(author)
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Detection of the interfacial exchange field at a ferromagnetic insulator-nonmagnetic metal interface with pure spin currents
- 2018
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In: Physical Review B. - 2469-9969 .- 2469-9950. ; 98:2
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Journal article (peer-reviewed)abstract
- At the interface between a nonmagnetic metal (NM) and a ferromagnetic insulator (FI) spin current can interact with the magnetization, leading to a modulation of the spin current. The interfacial exchange field at these FI-NM interfaces can be probed by placing the interface in contact with the spin transport channel of a lateral spin valve (LSV) device and observing additional spin relaxation processes. We study interfacial exchange field in lateral spin valve devices where a Cu spin transport channel is in proximity with ferromagnetic insulator EuS (EuS-LSV) and yttrium iron garnet Y3Fe5O12 (YIG-LSV). The spin signals were compared with reference lateral spin valve devices fabricated on nonmagnetic Si/SiO2 substrate with MgO or AlOx capping. The nonlocal spin valve signal is about 4 and 6 times lower in the EuS-LSV and YIG-LSV, respectively. The suppression in the spin signal has been attributed to enhanced surface spin-flip probability at the Cu-EuS (or Cu-YIG) interface due to an interfacial spin-orbit field. Besides spin signal suppression we also found a widely observed low temperature peak in the spin signal at T similar to 30 K is shifted to higher temperature in the case of devices in contact with EuS or YIG. Temperature dependence of the spin signal for different injector-detector distances reveal fluctuating exchange field at these interfaces cause additional spin decoherence which limit spin relaxation time in addition to conventional sources of spin relaxation. Our results show that temperature-dependent measurement with pure spin current can be used to probe interfacial exchange field at the ferromagnetic insulator-nonmagnetic metal interface.
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| 14. |
- Muduli, Pranaba, et al.
(author)
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Strong dependence of the magnetic anisotropy on the growth temperature of Fe3+xSi1-x (x=0.34) films on GaAs(113)A substrates
- 2009
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In: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 321:20, s. 3488-3492
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Journal article (peer-reviewed)abstract
- 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.
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| 15. |
- Pogoryelov, Ye., et al.
(author)
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Combined wide-narrow double modulation of spin-torque oscillators for improved linewidth during communication
- 2012
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In: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 48:11, s. 4077-4080
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Journal article (peer-reviewed)abstract
- 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 W = 500 MHz), modulation signal to improve the STO linewidth. At the same time we use a low-frequency, narrow (f N = 40 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.
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| 16. |
- Sharma, R., et al.
(author)
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A high-speed single sideband generator using a magnetic tunnel junction spin torque nano-oscillator
- 2017
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7:1
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Journal article (peer-reviewed)abstract
- An important property of spin-torque nano-oscillators (STNOs) is their ability to produce a frequency modulated (FM) signal, which is very critical for communication applications. We here demonstrate a novel single sideband (SSB) modulation phenomenon using a magnetic tunnel junction (MTJ)-based STNO, which saves transmission bandwidth and in principle should minimize attenuation for wireless communication. Experimentally, lower single sidebands (LSSBs) have been successfully demonstrated over a wide range of modulation frequency, f m = 150 MHz-1 GHz. The observed LSSBs are determined by the intrinsic properties of the device, which can be modeled well by a nonlinear frequency and amplitude modulation formulation and reproduced in macrospin simulations. Moreover, our macrospin simulation results show that the range of modulation current and modulation frequency for generating SSBs can be controlled by the field-like torque and biasing conditions. © 2017 The Author(s).
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| 17. |
- Sharma, R., et al.
(author)
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Enhanced Modulation Bandwidth of a Magnetic Tunnel Junction-Based Spin Torque Nano-Oscillator Under Strong Current Modulation
- 2021
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In: Ieee Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 42:12, s. 1886-1889
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Journal article (peer-reviewed)abstract
- The modulation bandwidth (f(BW)) is a critical figure-of-merit for wireless communication applications of spin torque nano-oscillators (STNOs) as it determines the maximum data rate. Although both theory and previous experiments have shown that f(BW) in STNOs is governed by the amplitude relaxation frequency f(p), we here demonstrate, using single-shot time-resolved measurements of a magnetic tunnel junction based STNO, that it can be many times larger under strong modulation. The behavior is qualitatively reproduced in macrospin simulations. Our results show that f(BW) of STNOs is not as limiting a factor for future wireless applications as previously believed.
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| 18. |
- Sharma, Raghav, et al.
(author)
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Enhanced Modulation Bandwidth of a Magnetic Tunnel Junction-Based Spin Torque Nano-Oscillator Under Strong Current Modulation
- 2021
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In: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 42:12, s. 1886-1889
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Journal article (peer-reviewed)abstract
- The modulation bandwidth (f(BW)) is a critical figure-of-merit for wireless communication applications of spin torque nano-oscillators (STNOs) as it determines the maximum data rate. Although both theory and previous experiments have shown that f(BW) in STNOs is governed by the amplitude relaxation frequency f(p), we here demonstrate, using single-shot time-resolved measurements of a magnetic tunnel junction based STNO, that it can be many times larger under strong modulation. The behavior is qualitatively reproduced in macrospin simulations. Our results show that f(BW) of STNOs is not as limiting a factor for future wireless applications as previously believed.
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| 19. |
- Sharma, R., et al.
(author)
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Time-domain stability of parametric synchronization in a spin-torque nano-oscillator based on a magnetic tunnel junction
- 2017
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 96:2
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Journal article (peer-reviewed)abstract
- We report on time-domain stability of the parametric synchronization in a spin-torque nano-oscillator (STNO) based on a magnetic tunnel junction. Time-domain measurements of the instantaneous frequency (f(i)) of a parametrically synchronized STNO showrandom short-term unlocking of the STNO signal for low injected radio-frequency (RF) power, which cannot be revealed in time-averaged frequency domain measurements. Macrospin simulations reproduce the experimental results and reveal that the random unlocking during synchronization is driven by thermal fluctuations. We show that by using a high injected RF power, random unlocking of the STNO can be avoided. However, a perfect synchronization characterized by complete suppression of phase noise, so-called phase noise squeezing, can be obtained only at a significantly higher RF power. Our macrospin simulations suggest that a lower temperature and a higher positive ratio of the fieldlike torque to the spin transfer torque reduce the threshold RF power required for phase noise squeezing under parametric synchronization.
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| 20. |
- Tiwari, D., et al.
(author)
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Influence of MgO barrier quality on spin-transfer torque in magnetic tunnel junctions
- 2018
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 112:2
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Journal article (peer-reviewed)abstract
- We studied the bias dependence of spin transfer torque in the MgO-based magnetic tunnel junction using a field-modulated spin torque ferromagnetic resonance measurement technique for three devices with tunneling magnetoresistances (MRs) of 60%, 67%, and 73%, respectively. The devices with a lower MR ratio showed the presence of multiple modes, while the device with higher MR (73%) showed a single resonance mode. We found a lower out-of-plane torkance in our devices compared to the in-plane torkance. The out-of-plane torque is linear with applied bias, while the bias dependence of in-plane torque shows a strong dependence on the MR ratio and hence the barrier quality. Published by AIP Publishing.
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