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, fm = 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.
Highlights
A nanopillar consisting of two magnetic layers, one free and one fixed, separated by a non-magnetic layer can be used as a tunable radio-frequency (RF) generator by using the concept of spin transfer torque[1,2]
The single sideband (SSB) modulation is a modulation scheme that requires less power to transmit than conventional amplitude modulation (AM) and occupies only half of the bandwidth required for other modulation schemes, like double-sideband suppressed carrier (DSB-SC)
The additional RF signal with relatively low frequency is analogous to the information that needs to be sent with the high-frequency carrier generated by the spin torque nano-oscillators (STNOs)
Summary
A nanopillar consisting of two magnetic layers, one free and one fixed, separated by a non-magnetic layer can be used as a tunable radio-frequency (RF) generator by using the concept of spin transfer torque[1,2]. The ASK modulation scheme was used to demonstrate wireless communication of STNO signals[24,25,26] up to a distance of 100 cm This demonstration provides an initial breakthrough in the field of signal transmission, and especially for digital signal processing using nanosized STNOs. In many wireless communication applications, the primary baseband signal is naturally generated in the form of analog signal, such as a voice or audio signal, and additional circuitry is required for the analog-to-digital conversion. We demonstrate lower single sideband (LSSB) modulation rates up to 1 GHz, taking advantage of the STNO’s nonlinear properties This advancement in SSB through STNOs opens up a new dimension of applications that are approachable, fast, and practical for on-chip technology. Using macrospin simulations, we show that the field-like torque can be used to manipulate the range of modulation current Im and modulation frequency fm for observing the SSB
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