High-frequency giant magnetoresistance measurement to study the dynamics of a micron-scale spin-valve sensor

We report on the study of the magnetization dynamic of a single micrometric spin-valve element by high-frequency giant magnetoresistance measurement. We have combined transport measurements in the microwave range and large band ferromagnetic resonance with microantennas. The spin valve is used as an in situ demodulator to probe the individual dynamics of each layer and the relative phase of their oscillations. We deduce the conditions for coupling the hard and free layer dynamics and show the influence of a static magnetic configuration on the sensitivity of spin valves in the microwave range. This work offers a different approach for studying the dynamics of single isolated micron-sized systems.

Figure 1

(Color online) (Top) Dimensions of the sensor designed as a yoke shape (gray) and the contact pads (delimited by black lines). (Middle) Dimensions of the shorted antenna. All dimensions are given in $\mu \text{m}$. (Bottom) System of axis and relative orientation of the different magnetic quantities.

Figure 2

(Color online) Resonance frequency of the spin valve as a function of $H_0$ (black squares) and fit obtained with Eq. (1) (red line). The parameters of the fit are given in the text. The inset presents the ferromagnetic linewidth as a function of the resonance frequency (black circles) and linear fit (black line) $\Delta H=\alpha {\omega }_r/\gamma {\mu }_0$ with $\alpha =0.026$.

Figure 3

(Color online) Demodulated signal as a function of the pumping field frequency measured with a spectrum analyzer in the parallel magnetic orientation of the free and hard layer at 100 (black square) and 320 Oe (green square). The black and orange lines correspond to the fit with Eq. (4) for 100 and 320 Oe, respectively. The blue and magenta lines correspond to the fit with Eq. (5) for 100 and 320 Oe, respectively. The red and violet lines correspond to the fit with Eq. (5) including the dynamic dipolar coupling.

Figure 4

(Color online) Ratio of the experimental over the simulated signal as a function of the pumping field frequency for 100 Oe (black), 320 Oe (orange), and the two layers precession model at 100 (blue) and 320 Oe (magenta) without including the dipolar coupling.