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Davies J.E.,Nve Corporation | Gilbert D.A.,University of California at Davis | Mohseni S.M.,KTH Royal Institute of Technology | Mohseni S.M.,NanOsc AB | And 5 more authors.
Applied Physics Letters | Year: 2013

We have observed distinct temperature-dependent magnetization reversal modes in a perpendicular (Co/Pd)4/Co/Cu/(Co/Ni)4/Co pseudo-spin-valve, which are correlated with spin-transport properties. At 300 K, magnetization reversal occurs by vertically correlated domains. Below 200 K the hysteresis loop becomes bifurcated due to laterally correlated reversal of the individual stacks. The magnetic configuration change also leads to higher spin disorders and a significant increase in the giant magnetoresistance effect. First order reversal curve measurements reveal that the coupled state can be re-established through field cycling and allow direct determination of the interlayer coupling strength as a function of temperature. © 2013 AIP Publishing LLC. Source


Mohseni S.M.,KTH Royal Institute of Technology | Mohseni S.M.,NanOsc AB | Sani S.R.,KTH Royal Institute of Technology | Sani S.R.,NanOsc AB | And 7 more authors.
Physica Status Solidi - Rapid Research Letters | Year: 2011

We demonstrate a nano-contact based spin-torque oscillator (STO) combining a high operating frequency with low field operation. The STO is based on an orthogonal spin-valve architecture with an in-plane Co polarizer and an out-of-plane Co/Ni multilayer free layer. High frequency operation at low external fields is achieved by tailoring the Co/Ni layer properties to increase the strength (Hk) of the perpendicular magnetic anisotropy, while simultaneously reducing the saturation magnetization (Ms). Our approach emphasizes the importance of μ0(Hk-Ms) in determining the operating frequency in this system, and suggests that yet higher frequencies should be attainable through further optimization. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) In this Letter the authors demonstrate a nanocontact spin-torque oscillator (STO) based on an orthogonal spin-valve architecture with an in-plane Co polarizer and an out-of-plane Co/Ni multilayer free layer. High frequency operation at low external fields is achieved by tailoring the Co/Ni layer properties to increase the strength of the perpendicular magnetic anisotropy, while simultaneously reducing the saturation magnetization. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Eklund A.,KTH Royal Institute of Technology | Bonetti S.,Stanford University | Sani S.R.,KTH Royal Institute of Technology | Majid Mohseni S.,KTH Royal Institute of Technology | And 10 more authors.
Applied Physics Letters | Year: 2014

The nano-scale spin torque oscillator (STO) is a compelling device for on-chip, highly tunable microwave frequency signal generation. Currently, one of the most important challenges for the STO is to increase its longer-time frequency stability by decreasing the 1/f frequency noise, but its high level makes even its measurement impossible using the phase noise mode of spectrum analyzers. Here, we present a custom made time-domain measurement system with 150 MHz measurement bandwidth making possible the investigation of the variation of the 1/f as well as the white frequency noise in a STO over a large set of operating points covering 18-25 GHz. The 1/f level is found to be highly dependent on the oscillation amplitude-frequency non-linearity and the vicinity of unexcited oscillation modes. These findings elucidate the need for a quantitative theoretical treatment of the low-frequency, colored frequency noise in STOs. Based on the results, we suggest that the 1/f frequency noise possibly can be decreased by improving the microstructural quality of the metallic thin films. © 2014 AIP Publishing LLC. Source


Chen T.,KTH Royal Institute of Technology | Durrenfeld P.,Gothenburg University | Rodriguez S.,KTH Royal Institute of Technology | Akerman J.,KTH Royal Institute of Technology | And 3 more authors.
Microwave and Optical Technology Letters | Year: 2014

This article presents a fully ESD-protected, highly tunable microwave oscillator based on magnetic tunnel junction (MTJ) spin torque oscillator (STO) technology. The oscillator consists of a compact MTJ STO and a 65 nm CMOS wideband amplifier, which amplifies the RF signal of the MTJ STO to a level that can be used to drive a PLL. The (MTJ STO+amplifier IC) pair shows a measured quality factor (Q) of 170 and a wide tunability range from 3 to 7 GHz, which demonstrate its potential to be used as a microwave oscillator in multiband, multistandard radios. © 2014 Wiley Periodicals, Inc. Source


Dumas R.K.,Gothenburg University | Iacocca E.,Gothenburg University | Bonetti S.,Stanford University | Sani S.R.,KTH Royal Institute of Technology | And 10 more authors.
Physical Review Letters | Year: 2013

It has been argued that if multiple spin wave modes are competing for the same centrally located energy source, as in a nanocontact spin torque oscillator, that only one mode should survive in the steady state. Here, the experimental conditions necessary for mode coexistence are explored. Mode coexistence is facilitated by the local field asymmetries induced by the spatially inhomogeneous Oersted field, which leads to a physical separation of the modes, and is further promoted by spin wave localization at reduced applied field angles. Finally, both simulation and experiment reveal a low frequency signal consistent with the intermodulation of two coexistent modes. © 2013 American Physical Society. Source

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