| 1. |
- Bonetti, Stefano, et al.
(författare)
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Buried tantalate-niobate microwave varactors
- 2007
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Ingår i: 2006 15TH IEEE INTERNATIONAL SYMPOSIUM ON APPLICATIONS OF FERROELECTRICS. - 9781424413317 ; , s. 347-350
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Konferensbidrag (refereegranskat)abstract
- We present characteristics of microwave variable capacitors (varactors) buried in 2.5 mu m thick AgTa0.5Nb0.5O3 (ATN) film pulsed laser deposited on sapphire single crystal. 2 gm gap interdigital capacitors (IDC) were fabricated by photolithographic, dry etching and lift-off processes. For comparison, similar IDCs were also defined on top of ATN film. Capacitance and loss tangent have been determined using a modified de-embedding technique in the microwave range 25 MHz - 40 GHz. Buried structures show higher values of capacitance and tunability, keeping the same level of losses compared to standard topped devices and resulting in an increased K-factor = tunability/tan delta. Experimental results are explained within equivalent circuit model. Besides the increased performance, the new design avoids the need of a successive planarization step, which could be required in an integration process.
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| 2. |
- Bonetti, Stefano, et al.
(författare)
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Spin torque oscillator frequency versus magnetic field angle : The prospect of operation beyond 65 GHz
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:10
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
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| 4. |
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| 5. |
- Zha, Chaolin, et al.
(författare)
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Pseudo-spin-valve with L1(0) (111)-oriented FePt fixed layer
- 2009
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 105:7, s. 07E910-
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Tidskriftsartikel (refereegranskat)abstract
- Recently we proposed a spin torque oscillator where the fixed layer has its magnetization easy-axis tilted with respect to the film plane to simultaneously achieve zero-field operation and high output power [Y. Zhou, C. L. Zha, S. Bonetti, J. Persson, and J. angstrom kerman, Appl. Phys. Lett. 92, 262508 (2008)]. Here we take the first step toward the realization of this device and fabricate successfully a pseudo-spin-valve using an L1(0) (111)-oriented FePt fixed layer with tilted magnetocrystalline anisotropy. A total magnetoresistance (MR) of 0.86% is experimentally observed for the standard pseudo-spin-valve of the L1(0) FePt/Cu/NiFe structure in applied fields up to 1.5 T. While part of the MR may originate from the FePt film alone, the dominating part of MR correlates with switching of the NiFe free layer.
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| 6. |
- Zha, Chaolin, et al.
(författare)
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Pseudo spin valves based on L10 (111)-oriented FePt fixed layers with tilted anisotropy
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate magnetoresistance (MR) in excess of 4% in FePt/CoFe/Cu/CoFe/NiFe pseudo spin valves based on L10 (111)-oriented FePt fixed layers with a 36 degrees out-of-plane tilted magnetization. The high MR is achieved by increasing the spin polarization at the Cu interfaces, using thin CoFe, and optimizing the FePt growth and Cu interface quality using Ta and Ta/Pt underlayers. We observe well-separated switching of the FePt/CoFe fixed layer and the CoFe/NiFe free layer, suggesting that CoFe is rigidly exchange coupled to FePt and NiFe in the respective layers.
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| 7. |
- Zhou, Yan, et al.
(författare)
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Capacitance Enhanced Synchronization of Pairs of Spin-Transfer Oscillators
- 2009
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Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 45, s. 2421-2423
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Tidskriftsartikel (refereegranskat)abstract
- Macro-spin simulations have been performed to study the synchronization of pairs of serially connected spin torque oscillators in parallel with a capacitor. The sensitivity to the STO process variation, which is modeled by the anisotropy field distribution for different STO samples, can be dramatically decreased by the coupling of a capacitor in the circuit. There exists an optimum capacitance where the multi-STO synchronized state develops the highest robustness.
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| 8. |
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| 9. |
- Zhou, Yan, et al.
(författare)
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Microwave generation of tilted-polarizer spin torque oscillator
- 2009
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 105:7, s. 07D116-
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Tidskriftsartikel (refereegranskat)abstract
- Microwave frequency generation in a spin torque oscillator (STO) with a tilted fixed layer magnetization is studied using numerical simulation of the Landau-Lifshitz-Gilbert-Slonczewski equation. The dependence of the STO free layer precession frequency on drive current is determined as a function of fixed layer tilt angle. We find that zero-field STO operation is possible for almost all tilt angles, which allow for great freedom in choosing the detailed layer structure of the STO.
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