O. Kovalenko, T. Pezeril, V. Temnov
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J. Janušonis, T. Jansma, C. L. Chang, Q. Liu, A. Gatilova, A. M. Lomonosov, V. Shalagatskyi, T. Pezeril, V. V. Temnov, R. I. Tobey
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Fig. 2: Magneto-elastic switching diagram in Terfenol-D. Starting in state 2 the magnetization vector can switch into all other energy minima 1,3 and 4. Both the acoustic pulse duration τac and strain amplitude ηac are important.
Fig. 1: (a) The magneto-elastic free energy density of a thin (110) layer of Terfenol-D possesses four in-plane energy minima, which correspond to four metastable magnetization directions 1,2,3 and 4. (b) Dynamics of magnetization vector induced by a sequence of ultrafast acoustic tensile pulses with amplitude of 0.9% and duration of 3ps. The acoustically induced ‘out-of-plane’kick of the magnetization vector leads to the decay into the neighboring energy minimum, i.e. switching occurs. The dashed contour shows the magnetization trajectory in the absence of damping.
We have developed a detailed theoretical understanding of ultrafast magneto-acoustic interactions in Rare Earth compound Terfenol-D. The free energy density of a thin Rare Earth Terfenol-D sample possesses four in-plane energy minima, which are very sensitive to the applied strain (see Fig. 1). The application of ultrafast acoustic strain pulses to Terfenol-D sample can be adequately described by Landau-Lifshitz-Gilbert equation. Whereas technical details of our calculations can be find online, here we briefly mention the most essential results of our theoretical modeling. The action of an ultrafast acoustic pulse, with duration much shorter than the ferromagnetic precession time (~25 ps), results in the out-of-plane kick of magnetization vector followed by its precession. If the amplitude of acoustic kick exceeds a certain threshold value (~20 degree), the magnetization decays into another minimum, i.e. magnetization switching occurs. The switching behavior can be best visualized in a magneto-elastic switching diagram (Fig. 2). The magnitude of the product τac x ηac of acoustic pulse duration τac by strain amplitude ηac largely determines the switching behavior. Experimentally accessible acoustic pulses with ηac = 1% and τac = 3 ps should be sufficiently strong to switch magnetization in Terfenol-D. The application of the developed theory to the experimental results (obtained within the frame work of this proposal), will be crucial to guide the experimental efforts towards demonstration of ultrafast magneto-elastic switching.
Ultrafast magnetoacoustics in Terfenol