Electrical Measurement of Spin-Wave Interactions of Proximate Spin Transfer Nanooscillators

We have investigated the interaction mechanism between two nanocontact spin transfer oscillators made on the same magnetic spin valve multilayer. The oscillators phase lock when their precession frequencies are made similar, and a giant magnetoresistance signal is detectable at one contact due to precession at the other. Cutting the magnetic mesa between the contacts with a focused-ion beam modifies the contact outputs, eliminates the phase locking, and strongly attenuates the magnetoresistance coupling, which indicates that spin waves rather than magnetic fields are the primary interaction mechanism.

Figure 1

Phase locking of two nanocontacts $c1$ and $c2$, spaced at 500 nm. System schematic shown at bottom right. (a) Frequency $f$ vs $I$ for each contact, with other contact at $I=0$. Inset: Spectrum for $I_{c1}=9.5\mathrm{mA}$. (b) Contour plot of combined spectral output for $I_{c1}=8\mathrm{mA}$, $I_{c2}$ swept from 5 to 11 mA. Color denotes measured power. (c) Powers from peak at $\approx 11\mathrm{GHz}$ in combined, $c1$, and $c2$ outputs during measurement in (b). Circles: Measured powers from each contact. Squares: Measured combined powers. Down triangles: Mathematical sum of $c1$ and $c2$. Up triangles: Coherent sum of $c1$ and $c2$ at zero relative phase.

Figure 2

Output from device measured in Fig. 1 after FIB cutting. For all panels, current $I_{c1}$ swept, $I_{c2}=6.75\mathrm{mA}$. (a) Coherently combined powers. Inset: Electron micrograph of contacts showing cut. (b)–(c) Outputs from $c1$ and $c2$, respectively. (d) Measured powers. Circles: Powers from each contact. Squares: Measured combined $c1$ and $c2$ powers. Dotted line: Mathematical (incoherent) sum of $c1$ and $c2$.

Figure 3

Spectrum at one contact (detector) due to precession at the other (emitter), 200 nm separation. Schematics show emitting contact; arrow denotes measured contact. For all plots, $I_{\mathrm{emitter}}=6.5\mathrm{mA}$. (a) Output from emitter vs $I_d$. (b) Signal at detector. (c) Normalized power $P_{\mathrm{detector}}/P_{\mathrm{emitter}}$ vs $I_d$ for data in (a) and (b). Also shown: Data for FIB-cut mesa.

Figure 4

Phase locking for 200 nm contact spacing. (a) $f$ vs $I$ for each contact, with the other at $I=0$. (b) Contour plot of combined spectral output for $I_{c1}=6.75\mathrm{mA}$, $I_{c2}$ swept. (c),(d) Outputs from contacts $c1$ and $c2$, respectively, for $I_{c1}=6.75\mathrm{mA}$, $I_{c2}=\mathrm{\text{swept}}$.