Abstract:We demonstrate enhanced radio frequency (RF) detection sensitivity in a magnetic tunnel junction based spin torque oscillator (STO) using parametric synchronization. The parametric synchronization is observed above the auto-oscillation threshold of the STO and enhances the RF sensitivity at 2f0, where f0 is the auto-oscillation frequency. The maximum RF sensitivity for parametric synchronization at 2f0≃9 GHz is 16 mV/mW, while the maximum RF sensitivity at f0≃4.5 GHz without parametric synchronization is 12 mV… Show more
“…Hence, for higher field-like terms, the frequency of the upper sideband can lie below f max with finite power, leading to the disappearance of LSSB. Thus, the observation of LSSB in our experimental results indicates the presence of smaller field-like torque, which is consistent with our earlier work on similar devices 30 , 36 . Figure 5 Macrospin simulation results: Map of power vs. frequency and modulation current at I dc = 6.4 mA and f m = 500 MHz for ( a ) b f = 0, ( b ) b f = 0.25, and ( c ) b f = 0.5.…”
Section: Resultssupporting
confidence: 94%
“…The device diameter was used as a fitting parameter to match the threshold current with experiments. The parameters used for the simulation are similar to those in our earlier work 36 . An interlayer exchange coupling ( H IEC ) of 117 Oe, and field angle of 188° was used in the simulations to match the experimental frequency of the STNO.…”
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.
“…Hence, for higher field-like terms, the frequency of the upper sideband can lie below f max with finite power, leading to the disappearance of LSSB. Thus, the observation of LSSB in our experimental results indicates the presence of smaller field-like torque, which is consistent with our earlier work on similar devices 30 , 36 . Figure 5 Macrospin simulation results: Map of power vs. frequency and modulation current at I dc = 6.4 mA and f m = 500 MHz for ( a ) b f = 0, ( b ) b f = 0.25, and ( c ) b f = 0.5.…”
Section: Resultssupporting
confidence: 94%
“…The device diameter was used as a fitting parameter to match the threshold current with experiments. The parameters used for the simulation are similar to those in our earlier work 36 . An interlayer exchange coupling ( H IEC ) of 117 Oe, and field angle of 188° was used in the simulations to match the experimental frequency of the STNO.…”
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.
“…Another possible way of STD frequency increase was proposed in the work by Tiwari et al. [ 50 ] Enhanced RF detection sensitivity of STD using parametric synchronization was demonstrated experimentally. The parametric synchronization, which was shown in presence of the auto‐oscillation with frequency f 0 , amplified the sensitivity at doubled frequency 2 f 0 .…”
Section: High Resonant Frequency Std Designs (Exchange Coupling Influmentioning
Among a rich variety of emerging spintronic devices, spin‐torque diodes (STDs) are among the most interesting, from both a fundamental and an applied perspective. The spin‐torque diode effect occurs when a microwave alternating electric current injected into a magnetic tunneling junction (MTJ) is rectified due to the simultaneous actions of tunneling magnetoresistance and spin‐transfer torque. While the sensitivity of STDs observed in the initial research is rather modest (about 1.4 mV mW−1), after only a few years researchers have increased it to 200 kV W−1 and demonstrated rectification at nanowatt input powers, which radically exceeds the capabilities of mainstream Schottky diodes. This impressive progress is based on a deep understanding of the complex STD physics and on recent advances in MTJ fabrication technology. Herein, the experimental pathways toward increasing the sensitivity and extending the frequency range of STDs and theoretical works aimed at explaining the complex nonlinear dynamics are analysed, and a wide variety of possible STD applications are discussed.
“…First, it allows accurate determination of non-linear parameters of STNOs as it favors one single excited mode [30,31,34]. Secondly, parametric synchronization can also be used to get an enhanced spin torque diode effect at a higher frequency [36]. In the context of this work, parametric synchronization greatly simplifies the measurement in time-domain.…”
We report on time-domain stability of the parametric synchronization in a spin-torque nanooscillator (STNO) based on a magnetic tunnel junction. Time-domain measurements of the instantaneous frequency (fi) of a parametrically synchronized STNO show random 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 field-like torque to the spin transfer torque reduce the threshold RF power required for phase noise squeezing under parametric synchronization.
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