Ensemble-averaged Rabi oscillations in a ferromagnetic CoFeB film

Abstract

Rabi oscillations describe the process whereby electromagnetic radiation interacts coherently with spin states in a non-equilibrium interaction. To date, Rabi oscillations have not been studied in one of the most common spin ensembles in nature: spins in ferromagnets. Here, using a combination of femtosecond laser pulses and microwave excitations, we report the classical analogue of Rabi oscillations in ensemble-averaged spins of a ferromagnet. The microwave stimuli are shown to extend the coherence-time resulting in resonant spin amplification. The results we present in a dense magnetic system are qualitatively similar to those reported previously in semiconductors which have five orders of magnitude fewer spins and which require resonant optical excitations to spin-polarize the ensemble. Our study is a step towards connecting concepts used in quantum processing with spin-transport effects in ferromagnets. For example, coherent control may become possible without the complications of driving an electromagnetic field but rather by using spin-polarized currents.

Laser-induced torques in metallic ferromagnets

“…Using femtosecond laser-pulses to switch the magnetization [1,2], to exert torques on the magnetic moments [3][4][5][6][7][8][9][10][11], to move domain walls [12], and to excite magnons [13] are promising concepts to write, store and process information on ultrafast timescales in prospective device applications. In bulk crystals laser-induced torques on the magnetization are attributed to the inverse Faraday effect (IFE) and to the optical spin-transfer torque (OSTT) [3,4,11].…”

Large spatial Schrödinger cat state using a levitated ferrimagnetic nanoparticle

“…It determines how a spin system loses energy and angular momentum. In the absence of inhomogeneity, Gilbert damping is related to the spin coherence time t 0 via the relation t 0 =1/αγ r B [50], where γ r is the gyromagnetic ratio and B is the magnetic field. α=1×10 −5 has been measured at 20K and according to the theory, in the absence of inhomogeneity-valid for small nanoparticles, it should vanish as the temperature decreases [49].…”

“…For homogeneous isotropic material T 1 = T 2 [37,38]. In ferromagnetic materials, the usage of T 1 and T 2 is not prevalent rather Gilbert damping α, which characterizes how a spin system loses energy and angular momentum, is widely used [39][40][41]. Nevertheless, α, T 1 and T 2 are intricately related with each other [41,42].…”

“…In ferromagnetic materials, the usage of T 1 and T 2 is not prevalent rather Gilbert damping α, which characterizes how a spin system loses energy and angular momentum, is widely used [39][40][41]. Nevertheless, α, T 1 and T 2 are intricately related with each other [41,42]. In the absence of any inhomogeneities [42], valid for small nanocrystals, coherence time is given by τ = 1/(αγB), where B is the magnetic field and γ is the gyromagnetic ratio.…”

“…In the absence of any inhomogeneities [42], valid for small nanocrystals, coherence time is given by τ = 1/(αγB), where B is the magnetic field and γ is the gyromagnetic ratio. In a recent experiment Capua et al [41] have measured both α and τ using a polycrystalline bulk CoFeB film sandwiched between multiple capping layers at room temperature. The coherence time of the overall film, 20×20 µm 2 in size, was about 0.5 ns but it was increased to ≈ 15 ns when a subset of the spins was selected.…”