Coherent high-amplitude precession of the magnetization and spin waves with frequencies up to 40 GHz are generated by injecting picosecond compressive and shear acoustic pulses into nanometer-sized galfenol (Fe81Ga19) films. The magnetization modulation is due to the picosecond inverse magnetostrictive effect. The oscillations of the magnetization measured by magneto-optical Kerr rotation last for several nanoseconds, and the maximum modulation of the in-plane effective magnetic field is as high as 40 mT. These results in combination with a comprehensive theoretical analysis show that galfenol films possess excellent properties for ultrafast magnetization control based on the picosecond inverse magnetostrictive effect.
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The parameter values are given in accordance with the expression for the free energy density described in Ref. 25. For better agreement we also add the lower-order in-plane magneto-elastic term in the form A2⊥εzzmxmy.
The magnetization direction is described by polar angle, θ, and azimuthal angle, ϕ.33 In ferromagnetic materials such as Fe (Ref. 31) and (Ga,Mn)As,32 the in-plane uniaxial anisotropy or saturation magnetization, respectively, are small, and H‖z modifies only one angle θ. This results in one minimum in the dependence f(H) (H‖z). In galfenol H modifies both angles, θ and φ, resulting in double minima in f(H).
The magnetic anisotropy of the films determined by superconducting quantum interference device (SQUID) magnetometry reveal that for the Fe81Ga19 film grown on the (001)-GaAs substrate the in-plane anisotropy consists of a superposition of a cubic term favoring the [100]/[010] directions and a uniaxial term favoring the [110] direction. For the Fe81Ga19 film deposited on the (311)-GaAs substrate, we measure the easy axis lying along the [−233] direction, in accordance with Ref. 34.
