Abstract
Frequency conversion forms an integral block of the electronic circuits used in various applications including energy harvesting, communications and signal processing. These frequency conversion units however require external power sources and occupy a large device footprint making it difficult to be integrated in micro-circuits. Here we demonstrate that nanoscale magnetic tunnel junctions can act as frequency converters without an external power supply or DC bias source. The device directly mixes an external microwave signal with the internal spin precession oscillations to create new frequencies tunable by an external magnetic field in a single device with a small device footprint. We observe up-conversion and down-conversion of the input signal for excitation frequencies between 2 GHz and 6 GHz. We also show that the device acts as a zero-bias rectifier that can generate voltages exceeding 12 mV when the excitation frequency matches the natural oscillations mode of the device.
Highlights
The ability to perform signal frequency conversion plays an important role in various applications that include communication, analog circuits, sensing, and power electronics
By injecting microwave signal wirelessly into the device, we show that it can generate both an up-converted and down-converted frequency signal that is tunable by an external magnetic field
We show that the device acts as a passive microwave rectifier for low input power levels, and is compatible with low voltage applications
Summary
The ability to perform signal frequency conversion plays an important role in various applications that include communication, analog circuits, sensing, and power electronics. Nanoscale magnetic tunnel junctions provide an alternate approach to achieve frequency conversion or rectification of low amplitude signals in a nanoscale device footprint These nano-oscillators take as their input direct currents and convert them to microwave current oscillations[6,7,8,9,10]. The microwave signal oscillations of the device, with modulation frequencies of up to 3.2 GHz12–14 These works required an external power supply to inject direct current to the device that generated microwave signal oscillations through nanoscale magnetic tunnel junctions. Whether such devices can attain frequency conversion passively without a dc bias current remained an important open question. These results open spintronic devices as potential passive frequency converters that may find important applications in signal processing, energy harvesting, and sensing
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