Abstract
Magnetization precession induced by linearly polarized optical excitation in ferromagnetic (Ga,Mn)As was studied by time-resolved magneto-optical Kerr effect measurements. The superposition of thermal and non-thermal effects arising from the laser pulses complicates the analysis of magnetization precession in terms of magnetic anisotropy fields. To obtain insight into these processes, we investigated compressively-strained thin (Ga,Mn)As films using ultrafast optical excitation above the band gap as a function of pulse intensity. Data analyses with the gyromagnetic calculation based on Landau-Lifshitz-Gilbert equation combined with two different magneto-optical effects shows the non-equivalent effects of in-plane and out-of-plane magnetic anisotropy fields on both the amplitude and the frequency of magnetization precession, thus providing a handle for separating the effects of non-thermal and thermal processes in this context. Our results show that the effect of photo-generated carriers on magnetic anisotropy constitutes a particularly effective mechanism for controlling both the frequency and amplitude of magnetization precession, thus suggesting the possibility of non-thermal manipulation of spin dynamics through pulsed laser excitations.
Highlights
Investigation of multiple functionalities of ferromagnetic semiconductors in the picosecond range lays the ground for future opportunities for high-speed spintronic devices
After the carriers transfer concentration by photoexcitation can modulate the magnitude of magnetic anisotropy fields, their excess energy to the lattice, the system acquires a quasi-equilibrium which reorients the direction of the easy axes, triggering the magnetization dynamics on a time temperature
We report a study of photoinduced collective spin excitation and their dynamics in ferromagnetic
Summary
Investigation of multiple functionalities of ferromagnetic semiconductors in the picosecond range lays the ground for future opportunities for high-speed spintronic devices. Time-resolved magneto-optical Kerr effect (MOKE) spectroscopy has been widely used for studying ultrafast photon-induced collective spin dynamics in ferromagnetic semiconductors. Based on this technique, Mn-based III–V ferromagnetic semiconductors have been extensively investigated from the point of view of both fundamental physics and spintronic applications [1,2,3,4,5,6]. Ultrafast magneto-optical investigation of collective spin excitations in ferromagnetic (Ga,Mn)As thin films has demonstrated the possible multi-functionality of ferromagnetic semiconductors when incorporated in spintronic devices [4,7,8,9]. Modulation of magnetic anisotropy stimulated by transient increases of either local temperature or photocarrier density in (Ga,Mn)As has demonstrated multiple possibilities of modulating the precession of magnetization by linearly polarized pump pulses
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