Frequency-Locking in Serially Coupled Spin Transfer Nano-Oscillators

Frequency-Locking in Serially Coupled Spin Transfer Nano-Oscillators
Spin transfer nano-oscillators; Magnetic tunnel junctions
Issue Date
2011년도 하계학술연구발표회 (한국자기학회)
More recently, the characteristics of microwave emission by spin torque induced magnetization precession in magnetic tunnel junctions (MTJ) have extensively been examined for radio frequency (rf) device applications [1]. Although the spin-transfer nano-oscillators (STNO) can present such an excellent frequency tunability in the GHz range and fully compatible with a high level of integration, there are two main drawbacks regarding the weak output power and broad spectral linewidth of the generation signals [2]. One of the solutions to overcome these problems is to synchronize many STNO devices by use of various local or non local mechanisms [3]. As one of the non local methods, we study on the interaction between electrically connected STNOs through spin transfer self-emitted microwave current. The fabricated device consists of a nominally 100 X 60 nm2 elliptical nanopillar structure composed of SiO2 substrate/Ta (5)/CuN (30)/Ta (5)/Pt37Mn63 (20)/Co70Fe30 (3)/Ru (0.8)/Co60Fe20B20 (5)/MgO (1)/Co60Fe20B20 (2)/Ta (10)/CuN (10)/Ru (7) (in nm). The STNO has the tunnel magnetoresistance (TMR) of 63 % and resistance-area (RA) product of 5 Ω·μ㎡ in the parallel state. With respect to the microwave measurement, the device is connected to a ground-signal-ground (GSG) probe with coplanar waveguide (CPW) pattern. And the rf output spectra are monitored by a spectrum analyzer through the bias-tee circuit including a DC bias input and a rf output signal port. The output signals are amplified by a 40 dB preamplifier, but both the amplification and background noise are subtracted for the presented data. All measurements are carried out at room temperature.
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