All optical detection of picosecond spin-wave dynamics in 2D annular antidot lattice

Abstract

Novel magnetic structures with precisely controlled dimensions and shapes at the nanoscale have potential applications in spin logic, spintronics and other spin-based communication devices. We report the fabrication of two-dimensional bi-structure magnonic crystal in the form of embedded nanodots in a periodic Ni80Fe20 antidot lattice structure (annular antidot) by focused ion-beam lithography. The spin-wave spectra of the annular antidot sample,studied for the first time by a time-resolved magneto-optic Kerr effect microscopy show a remarkable variation with bias field, which is important for the above device applications. The optically induced spin-wave spectra show multiple modes in the frequency range 14.7 GHz to 3.5 GHz due to collective interactions between the dots and antidots as well as the annular elements within the whole array. Numerical simulations qualitatively reproduce the experimental results, and simulated mode profiles reveal the spatial distribution of the spin-wave modes and internal magnetic fields responsible for these observations. It is observed that the internal field strength increases by about 200 Oe inside each dot embedded within the hole of annular antidot lattice as compared to pure antidot lattice and pure dot lattice. The stray field for the annular antidot lattice is found to be significant (0.8kOe) as opposed to the negligible values of the same for the pure dot lattice and pure antidot lattice. Our findings open up new possibilities for development of novel artificial crystals.

Observation of angle-dependent mode conversion and mode hopping in 2D annular antidot lattice

“…The exchange stiffness constant A is obtained from literature 42 . These parameters are consistent with our previous work 32 . To excite the precessional dynamics, a pulsed magnetic field of peak amplitude of 30 Oe, rise/fall time of 10 ps and pulse duration of 50 ps is applied perpendicular to the sample plane under a constant bias field of H = 1.08 kOe.…”

“…The sample is fabricated on e-beam evaporated permalloy (Ni 80 Fe 20 , Py hereon) film using focused ion beam lithography. The details of the sample fabrication are described elsewhere 32 . The thickness of the Py film is 15 nm.…”

“…The atomic force microscope (AFM) and magnetic force microscope (MFM) images of the sample are presented in ref. 32 . The ultrafast magnetization dynamics of the sample is measured by using an all-optical TR-MOKE microscope in polar Kerr geometry (see Fig.…”

Observation of spectral narrowing and mode conversion in two-dimensional binary magnonic crystal

“…In simulation, we apply a pulsed magnetic field of 30 Oe field strength and 10 ps rise/fall time, which reproduces the experimental conditions successfully. The method of the simulation can be found elsewhere [30]. The simulations are performed on smaller arrays of 2690 × 3190 µm 2 size using two-dimensional periodic boundary condition (PBC) after discretizing the arrays into cuboidal cells of 5 nm × 5 nm × 15 nm volumes.…”

“…The material parameters used for simulations are gyromagnetic ratio γ = 17.6 MHz Oe -1 , anisotropy field Hk = 0, saturation magnetization Ms = 860 emu cm -3 , and exchange stiffness constant A = 1.3 × 10−6 erg cm -1 [6]. Here, Ms value is taken from our previous work on 15-nm-thick Py film [30].…”