Chaotic magnetization dynamics driven by feedback magnetic field

An excitation of highly nonlinear, complex magnetization dynamics in a ferromagnet, for example chaos, is a new research target in spintronics. This technology is applied to practical applications such as random number generator and information processing systems. One way to induce complex dynamics is applying feedback effect to the ferromagnet. The role of the feedback electric current on the magnetization dynamics was studied in the past. However, there is another way to apply feedback effect to the ferromagnet, namely feedback magnetic field. In this paper, we developed both numerical and theoretical analyses on the role of the feedback magnetic field causing complex magnetization dynamics. The numerical simulation indicates the change of the dynamical behavior from a simple oscillation with a unique frequency to complex dynamics such as amplitude modulation and chaos. The theoretical analyses on the equation of motion qualitatively explain several features found in the numerical simulations, exemplified as an appearance of multipeak structure in the Fourier spectra. The difference of the role of the feedback electric current and magnetic field is also revealed from the theoretical analyses.