Low Temperatures Enterprise Domain Wall Ferromagnet Mesoscopic Quantum Dynamics Study

In this paper, we introduct the classical dynamics of a domain wall, including the correlative basic concept of magnetics, the static magnetization process, the dynamic magnetization process and wastage. On the basis of that, the classical motion equation of a domain wall was obtained and its characteristic was discussed in the phase space.lt was proved that the classical movement of a domain wall was damped oscillate.Uehara and Barbara demonstrated that the anomalous coercivity originates from the quantum tunneling effect or quantum transition of a quantum harmonic oscillator with zero-point energy but not from the marcoscopic movement of the small mesoscopic ferromagnetic domain walls at low temperature.In this paper, we analytically investigate the quantum behavior of a mesoscopic domain wall applied by time-dependent external magnetic field. Starting from the quantized Hamiltonian governing motion equation of a mesoscopic ferromagnetic domain wall at low temperature, the analytic wavefunction was obtained by using canonical quantization method and unitary transformation. Then, the quantum property of a mesoscopic domain wall was analyzed in three kinds of external magnetic field, including the static magnetic field, the periodical magnetic field and the random-like field. The orbit of the phase space in three kinds of external magnetic field was expressed by using Matlab 6.0 software, discussed and compared with the classical result. It is found that the motion of the wavepacket center representing the domain wall motion can exhibit the exact resonace behavior when the natural oscillatory frequency does not exactly coincide with the external magnetic field frequency.In addition, the quantum fluctuations of displacement and momentum of the domain wall are evaluated and are only influenced by the damped force but not by the external periodical magnetic field at all. Otherwise, the Wigner function was caculated and discussed.Finally, the investigations are summarized and further study is prospected to get improvements.