Figure 3 : Magnetoresistance measurement and magnetization dynamics of coupled vorticies with opposite vorticity.

From: Spin-torque-induced dynamics at fine-split frequencies in nano-oscillators with two stacked vortices

Figure 3

(a) Magnetoresistance measurement of an OV–DV state. As indicated by the red arrows along the magnetoresistance curve, the field B is swept from positive to negative values during the measurement of the resistance R. At the starting point of the field sweep (region I) the magnetization in the bottom disc is in a vortex state while the top disc is still in a single-domain state. At about 50 mT, the sample switches into the OV–DV state. The inset to region II displays the vorticity combination resulting in this particular measurement. In region II, the blue circles indicate the presence of excitations simultaneously recorded during the magnetoresistance measurement, which arise from coupled gyrotropic motion of the vortices. At −180 mT, the vortex is expelled from the top disc (region III), while in region IV both discs are saturated. The inset diagram in region IV shows the direction of electron flow. (b) High-frequency spectra measured during the field sweep displayed in a. The colour code represents the power density measured in pW GHz−1 in a logarithmic scale. The minimum and maximum values are shown on the colour bar.