Ultrafast magnetization dynamics in FeCo thin films with varied stoichiometry

Abstract

Despite the fact that numerous experiments have been conducted on a variety of magnetic materials, further research is necessary on the ultrafast magnetization dynamics of other magnetic materials. This is not only to understand the mechanism behind ultrafast demagnetization, but also to identify suitable materials for a range of applications. In this regards, FeCo alloys offers research possibility due to their high magnetic moment, low Gilbert damping factor, tunable Curie temperature and moderate composition-dependent spin–orbit coupling strength. In this work, time-resolved magneto optic Kerr effect (TR-MOKE) experimental techniques and three temperature model (3TM) analysis were used to investigate how compositional tuning affects the efficiency of demagnetization and it’s time scales. We found that, the demagnetization time for FeCo thin films, obtained by fitting the experimental TR-MOKE data to the analytical solution of 3TM, were ranging between 300 and 500 fs. Those values are slower than that of other transition metals. This observation was attributed to the low Gilbert damping factor \(\alpha \) value of the investigated FeCo thin films. Moreover, the values of both \(\tau _m\) and \(\tau _E\) were increased with increasing fluence values. It can be concluded from these two observations that the underlying mechanism responsible for the ultrafast demagnetization in FeCo thin films is predominantly governed by the spin–flip process. Additionaly, experimental results along with their theoretical analysis revealed that, although altering composition of FeCo thin films affect ultrafast demagnetization time profile slightly, it changes demagnetization efficiency significantly, which is one of the important parameters for ultrafast switching applications. Therefore, it can be concluded that among the investigated thin films Fe\(_{30}\)Co\(_{70}\) have the potential to be utilised in ultrafast switching applications.