Microwave spin-torque excitation in a template-synthesized nanomagnet

A microwave-compatible lithography-free process is shown to allow the electrical contact of a single nanometric spin valve grown by template synthesis. The complex spin dynamics of a single nanomagnet is revealed by resonant microwave current excitations, detected electrically in the $V_{\text{dc}}$ and second-harmonic voltages. The uniform modes are attributed to spin transfer torque effects, whereas the effect of oersted field may play a role in exciting the nonuniform modes.

Figure 1

(Color online) (a) Blown up view of the connector assembly fitted with a nanoporous membrane and gold wire contact. (b) Magnetoresistance cycle as a function of the applied field $H_0$. The field sweeps up (black) and down (red) from $-700$ to $+700\text{mT}$. The inset shows the structure of the spin valve.

Figure 2

(Color online) $V_{\text{dc}}$ (measured with a voltmeter) as a function of the ac frequency for (a) high and (b) low fields. The curves are shifted by $2\mu \text{V}$ for clarity. Numbers on the figure correspond to the amplitude of the external field $H_0$ in mT. (c) Signal at twice the excitation frequency (red) and $V_{\text{dc}}$ (black) recorded simultaneously. The harmonic signal is measured with a spectrum analyzer. The baseline (blue) is recorded at saturation field. Measurements of the harmonic signals are averaged 1000 times to increase the signal-to-noise ratio. (d) $dV/dI$ as a function of $I_{\text{dc}}$ observed in a similar structure.

Figure 3

(Color online) Evolution of the different resonant modes as a function of the applied field $H_0$. The red and black lines correspond to the fit with the macrospin model for the free and hard layers, respectively.