Propagation of spin wave pulses during time dependent magnetic fields


Propagation of spin wave pulses during time dependent magnetic fields

Nishida, N.; Matthies, P.; Wagner, K.; Schultheiss, K.; Schultheiss, H.

Spin wave dispersion relation depends on a magnetic field. The resonance frequency is higher for higher magnetic fields. While it was previously reported how spin waves adapt to spatially inhomogeneous magnetic fields [1], we investigated spin-wave propagation under the influence of nanosecond magnetic field pulses.
We fabricated a 2 µm-wide spin-wave waveguide from NiFe with an antenna for spin wave excitation and a dc line below the spin-wave conduit. An external magnetic field was applied perpendicular to the stripe. In order to modulate the internal magnetic field in the stripe, a dc pulse was injected into the dc line, because the dc pulse generates Oersted field. We measured a magnon density on the stripe using time-resolved Brillouin light scattering microscopy, and investigated spin-wave dynamics when the dc pulse came in. We succeeded to observe the temporal magnon density when the dc pulse came in and went out. For a fixed excitation frequency observed a decrease (increase) of the spin-wave frequency at the rising (falling) edge of the dc pulse. Since Oersted field is in the opposite direction to the external magnetic field, the internal magnetic field is lower than the external field while the dc pulse is on. The dispersion relation shifts to lower frequency, and it matches to the resonance magnetic field temporarily. At that time spin wave pulse is excited under the antenna. We also observed the position dependency of the excited spin wave pulse. The spin wave pulse propagated, and the frequency shifted lower at the rising edge of the dc pulse, or shifted higher at the falling edge of the dc pulse. We succeeded to observe the excited spin wave pulse following the change of the dispersion relation, and demonstrated the modulation of spin wave by the change of the magnetic field.

[1] V. E. Demidov et. al., Appl. Phys. Lett. 99, 082507 (2011).

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    Magnonics 2017, 07.-10.08.2017, Oxford, United Kingdom

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Publ.-Id: 26816