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▼ [16a-C41-6] Detection of voltage excited spin wave by pico-second time-resolved Kerr microscope
キーワード：Voltage control magnetic anisotropy, Spin wave, TRMOKE
Spin waves can be implemented in logic devices. Recent studies show that the RF voltage (VRF) can excite uniform magnetization dynamics in ultrathin ferromagnetic films via voltage control magnetic anisotropy (VCMA) with ultralow power consumption [1, 2]. In spite of some theoretical reports [3, 4], there is no experimental report on experimental detection of voltage excited spin wave. Here, we show detection of voltage excited spin wave by pico-second time-resolved magneto-optical Kerr-effect (ps-TRMOKE) microscope [5]. We fabricated spin wave devices from a stack of Si/Ta(5)/Ru(20)Ta(5)Co20Fe60B20(2)MgO(2)Al2O3(10) by a multistep fabrication process. The top Au electrode with lateral dimension of 2×10 μm2 is structured on the center of a wider ferromagnetic (CoFeB) waveguide which is used as the bottom electrode.
The spin waves are excited by modulating perpendicular magnetic anisotropy with VRF and measured by a linearly polarized pico-second (ps) pulsed laser beam focused with a spot size of about 600 nm in longitudinal MOKE geometry. The decay length (λd) of excited magnetostatic surface spin waves (MSSW) is about 2.1 µm at 10 mT bias magnetic field (H) and decreases monotonically to reach a value of 1.3 µm at H = 40 mT. The group velocity (vg) is about 0.25 µm ns-1 at 10 mT and also decreases slowly to reach a value of 0.2 µm ns-1 at H = 40 mT. We compared these values with the spin wave excited by a coplanar strip line (or Oersted field). It shows a reasonably good agreement. However the apparent decay length in the later case is larger than the former case due to the spatial distribution of the Oersted field outside the stripline. This shows the advantage of voltage excitation over Oersted field excitation. Moreover, spin wave amplitude monotonically increases with the increase of H, whereas for Oersted field excitation, the amplitude reaches to maxima and starts to decrease after that. These behaviors are supported by our micromagnetic simulations. We think our results have a large impact for the development of future spin wave based logic devices.
[1] T. Nozaki et al., Nat. Phys. 8, 491 (2012).
[2] J. Zhu et al., Phys. Rev. Lett. 108, 197203 (2012).
[3] R. Verba et al., Phys. Rev. Appl. 1, 044006 (2014).
[4] R. Verba et al., Sci. Rep. 6, 25018 (2016).
[5] A. Barman et al., Rev. Sci. Instrum.79, 123905 (2008).
The spin waves are excited by modulating perpendicular magnetic anisotropy with VRF and measured by a linearly polarized pico-second (ps) pulsed laser beam focused with a spot size of about 600 nm in longitudinal MOKE geometry. The decay length (λd) of excited magnetostatic surface spin waves (MSSW) is about 2.1 µm at 10 mT bias magnetic field (H) and decreases monotonically to reach a value of 1.3 µm at H = 40 mT. The group velocity (vg) is about 0.25 µm ns-1 at 10 mT and also decreases slowly to reach a value of 0.2 µm ns-1 at H = 40 mT. We compared these values with the spin wave excited by a coplanar strip line (or Oersted field). It shows a reasonably good agreement. However the apparent decay length in the later case is larger than the former case due to the spatial distribution of the Oersted field outside the stripline. This shows the advantage of voltage excitation over Oersted field excitation. Moreover, spin wave amplitude monotonically increases with the increase of H, whereas for Oersted field excitation, the amplitude reaches to maxima and starts to decrease after that. These behaviors are supported by our micromagnetic simulations. We think our results have a large impact for the development of future spin wave based logic devices.
[1] T. Nozaki et al., Nat. Phys. 8, 491 (2012).
[2] J. Zhu et al., Phys. Rev. Lett. 108, 197203 (2012).
[3] R. Verba et al., Phys. Rev. Appl. 1, 044006 (2014).
[4] R. Verba et al., Sci. Rep. 6, 25018 (2016).
[5] A. Barman et al., Rev. Sci. Instrum.79, 123905 (2008).