Imaging the dephasing of spin wave modes in a square thin film magnetic element

Abstract

We have used time-resolved scanning Kerr effect microscopy to study dephasing of spin wave modes in a square Ni 81 Fe 19 element of 10 m width and 150 nm thickness. When a static magnetic field H was applied parallel to an edge of the square, demagnetized regions appeared at the edges orthogonal to the field. When H was applied along a diagonal, a demagnetized region appeared along the opposite diagonal. Time-resolved images of the out-of-plane magnetization component showed stripes that lie perpendicular to H and indicate the presence of spin wave modes with wave vector parallel to the static magnetization. The transient Kerr rotation was measured at different positions along an axis parallel to H, and the power spectra revealed a number of different modes. Micromagnetic simulations reproduce both the observed images and the mode frequencies. This study allows us to understand an anisotropic damping observed at the center of the square element in terms of dephasing of the resonant mode spectrum.

Time-resolved investigation of magnetization dynamics of arrays of nonellipsoidal nanomagnets with nonuniform ground states

“…This results in a richer mode spectrum and hence in a less uniform magnetic response to a pulsed magnetic field, which can be directly imaged in the case of micrometer sized magnetic elements. [26][27][28][29][30][31][32] The dominant role of the long-range magnetodipole interaction in the phenomena observed so far makes their analytical description complicated and generally requires numerical solution of integrodifferential equations. However, the interpretation of the magnetization dynamics in nonellipsoidal elements at finite bias field values becomes even more involved and challenging since it is not only the effective internal magnetic field but also the static magnetization that is nonuniform.…”

Spin wave non-reciprocity and beating in permalloy by the time-resolved magneto-optical Kerr effect

“…Spin waves have been detected at distances up to 80 m away from a coplanar strip (CPS) line [23] in thin permalloy films using coplanar waveguides antennas. Studies on thin permalloy (Ni 80 Fe 20 ) films of different aspect ratios and geometries have reported the observation of mode interference of single-frequency spin waves in the k-space [23,26,27].…”

“…The finite size effect due to the lateral confinement of spin waves results in interference between spin wave modes revealing a spatial dependency of the spin wave intensity [14,16]. Time-resolved scanning Kerr microscopy (TRSKM) has a significantly higher temporal resolution (~20 ps) than BLS measurements, and this advantage has been used to explore the temporal characteristics of spin wave propagation [22][23][24][25][26]. Spin waves have been detected at distances up to 80 m away from a coplanar strip (CPS) line [23] in thin permalloy films using coplanar waveguides antennas.…”

Magnonic Logic Devices

“…Dependent on the magnetization orientation local standing spin wave modes are either excited or not in the ferromagnetic square that forms the junction. In contrast to the local spin wave modes intensively studied in standing alone square nano-magnets [46], the square in the cross center is subjected to non-uniform magnetic fi elds generated by the cross arms. Local standing spin wave modes in the center of the cross junction, if excited, in turn generate the outgoing spin waves in all four arms of the cross that form refl ected and scattered waves.…”