Research On Manipulating Ultrafast Magnetic Dynamics And Damping Of Perpendicularly Magnetized CoFeB Films

With the rapid development of information technology and quantum computation,the storage and read of data have been put forward more and more requirements for storage devices.As a new generation of applications,spintronic devices have shown promising prospects in the fields of quantum computers and spin transistors.The studies on spin-related physical phenomena have become an international forefront and a new discipline called as spintronics.Meanwhile,the development of ultrashort pulse laser technology provides a high temporal resolution tool with the studies on the interaction of light with materials and the microscopic processes in strong field physics,which promotes the ultrafast spin dynamics.However,some basic issues related to the mechanism of the ultrafast magnetization dynamics have not been understood completely.More experimental and theoretical studies on them are necessary.Therefore,a typical kind of material CoFeB are chosen and studied in detail to deepen understandings on the fundamental issues above.The contents are as follows:First of all,the spin relaxation dynamics of CoFeB films are studied by alternating the materials of buffer layer and capping layer and using time-resolved magneto-optical Kerr effect(TRMOKE) measurements.According to the results,it is found that the effective damping parameter is inversely proportional to the magnetic field and reaches to a constant finally,suggesting the Gilbert damping constant is inherent to CoFeB film.Furthermore,the Gilben damping constant is different in two series of CoFeB films and because the interface of CoFeB/Ta increase the electron-phonon scattering by increasing the mixing conductance.We can manipulate the Gilbert damping constant by the growth sequence.Secondly,current-induced influence on ultrafast magnetization dynamics in striped CoFeB is studied.By current dependent experiments,we found the impact of current's direction and size on the damping,which suggests that the current induces an effective field in the plane and change the relaxation.As well as,the Gilbert damping constant changes about 70 percent compared to the situation of no current when we turn off the current source.It provides a possibility that spin flips in spintronics devices.Finally,we study the ultrafast dynamics of CoFeB in different fluence of pump laser.Analyzing the results,the impact of different fluence on CoFeB is not the same and the Gilbert damping constant reach to the maximum.Combining the three temperature model,we found that the ratio of the system's temperature and the Curie temperature is changed and further change the Gilbert damping constant.This research suggests that the power has a significant role in reading and writing of storage devices.