| 1. |
- Bonetti, Stefano, 1982-, et al.
(författare)
-
Experimental evidence of self-localized and propagating spin wave modes in obliquely magnetized current-driven magnetic nanocontacts
- 2010
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 105:21, s. 217204-
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 2. |
|
|
| 3. |
- Bonetti, Stefano, et al.
(författare)
-
Power and linewidth of propagating and localized modes in nanocontact spin-torque oscillators
- 2012
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 85:17, s. 174427-
-
Tidskriftsartikel (refereegranskat)abstract
- The integrated power and linewidth of a propagating and a self-localized spin-wave mode excited by spin-polarized current in an obliquely magnetized magnetic nanocontact are studied experimentally as functions of the angle theta(e) between the external bias magnetic field and the nanocontact plane. It is found that the power of the propagating mode increases monotonically with theta(e), while the power of the self-localized mode has a broad maximum near theta(e) = 40 degrees and exponentially vanishes near the critical angle theta(e) = 58 degrees, at which the localized mode disappears. The linewidth of the propagating mode in the interval of angles 58 degrees < theta(e) < 90 degrees, where only this mode is excited, is adequately described by the existing theory, while in the angular interval where both modes can exist the observed linewidth of both modes is substantially broadened due to the telegraph switching between the modes. Numerical simulations and an approximate analytical model give a good semiquantitative description of the observed results.
|
|
| 4. |
- Bonetti, Stefano, et al.
(författare)
-
Spin torque oscillator frequency versus magnetic field angle : The prospect of operation beyond 65 GHz
- 2009
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:10
-
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.
|
|
| 5. |
|
|
| 6. |
- Muduli Kishor, Pranaba, 1978, et al.
(författare)
-
Spin Torque Oscillators and RF Currents—Modulation, Locking, and Ringing
- 2011
-
Ingår i: Integrated Ferroelectrics. - : Informa UK Limited. - 1058-4587 .- 1607-8489. ; 125:1
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 7. |
- Muduli, Pranaba, et al.
(författare)
-
Modulation of single and double spin torque oscillators
- 2011
-
Ingår i: AIP Conf. Proc.. - : AIP. ; 1347
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 8. |
- Muduli, Pranaba, et al.
(författare)
-
Nonlinear frequency and amplitude modulation of a nanocontact-based spin-torque oscillator
- 2010
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:14, s. 140408(R)-
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 9. |
- Pogoryelov, Yevgen, 1975, et al.
(författare)
-
Frequency modulation of spin torque oscillator pairs
- 2011
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 98:19
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 10. |
- Pogoryelov, Yevgen, 1975, et al.
(författare)
-
Spin-torque oscillator linewidth narrowing under current modulation
- 2011
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 98:19
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
