Detection of the Microwave Emission from a Spin-Torque Oscillator by a Spin Diode

Magnetic tunnel junctions are nanoscale spintronic devices with microwave-generation and -detection capabilities. Here, we use the rectification effect called a “spin diode” in a magnetic tunnel junction to wirelessly detect the microwave emission of another junction in the auto-oscillatory regime. We show that the rectified spin-diode voltage measured at the receiving junction end can be reconstructed from the independently measured auto-oscillation and spin-diode spectra in each junction. Finally, we adapt the auto-oscillator model to the case of the spin-torque oscillator and the spin diode and we show that it accurately reproduces the experimentally observed features. These results will be useful for the design of circuits and chips based on spintronic nanodevices communicating through microwaves.

Figure 1

(a) The schematic of the measurement setup. Both the spin-torque nano-oscillator and the spin diode are magnetic tunnel junctions, composed of two ferromagnets separated by a thin nonmagnetic layer (yellow). The magnetization of the bottom ferromagnet (gray) is pinned, whereas that of the top one (blue) is free. (b) The frequency (squares) and power (line) of the oscillator after 20 dB total gain after the amplifier and antennas as a function of the current $I_{\mathrm{dc}}$ extracted from the measured power spectra for two different oscillator fields $H=5200\mathrm{Oe}$ (red) and $H=5000\mathrm{Oe}$ (blue). (c) The measured rectified spin-diode voltage at $H_{\mathrm{diode}}=3000\mathrm{Oe}$ as a function of the microwave source frequency for different color-coded source powers.

Figure 2

The measured spin-diode voltage as a function of the current in the oscillator for different oscillator fields $H$. The dashed lines show the voltage reconstructed from the oscillator amplitude at a given current [shown for $H=5200\mathrm{Oe}$ and $H=5000\mathrm{Oe}$ in Fig. 1] and the spin-diode voltage at a given frequency [Fig. 1].

Figure 3

The measured spin-diode voltage as a function of the oscillator current for a fixed oscillator magnetic field $H=5200\mathrm{Oe}$ and for different amplifier gains $G$. The dashed lines correspond to voltages reconstructed from the oscillator amplitude at a given current [Fig. 1] and the spin-diode voltage for a given input frequency and power [Fig. 1].

Figure 4

The calculated spin-diode voltage (a) as a function of the source frequency for different source powers and (b) as a function of the oscillator current for different amplifying factors obtained by numerically solving the dynamics equation (3) (full line) and from the exact analytical solution (6) (dashed line).