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.
We introduce a new type of binary magnonic crystal, where Ni80Fe20 nanodots of two different sizes are diagonally connected forming a unit and those units are arranged in a square lattice. The magnetization dynamics of the sample is measured by using time-resolved magneto-optical Kerr effect microscope with varying magnitude and in-plane orientation (ϕ) of the bias magnetic field. Interestingly, at ϕ = 0°, the spin-wave mode profiles show frequency selective spatial localization of spin-wave power within the array. With the variation of ϕ in the range 0°<ϕ≤45°, we observe band narrowing due to localized to extended spin-wave mode conversion. Upon further increase of ϕ, the spin-wave modes slowly lose the extended nature and become fully localized again at 90°. We have extensively demonstrated the role of magnetostatic stray field distribution on the rotational symmetries obtained for the spin-wave modes. From micromagnetic simulations, we find that the dipoleexchange coupling between the nano-dots leads to remarkable modifications of the spin-wave mode profiles when compared with arrays of individual small and large dots. Numerically, we also show that the physical connection between the nano-dots provides more control points over the spin-wave propagation in the lattice at different orientations of bias magnetic field. This new type of binary magnonic crystal may find potential applications in magnonic devices such as spin-wave waveguide, filter, coupler, and other on-chip microwave communication devices. I. Introduction:Nanomagnets have huge applications in magnetic storage [1], memory [2], logic [3], sensors [4], other spintronics and biomedical devices [5,6]. One of the more recent and emerging fields based on nanomagnetism is magnonic crystals (MCs) [7], which are periodically modulated ferromagnetic materials, such as ferromagnetic nanodots [8], nanowire [9], nanoscale antidot arrays [10], where spin waves (SWs) are carrier waves. Due to their wavelength falling in the nanoscale regime for GHz to sub-THz frequency range spin-waves, MCs are ideally suited for nanoscale on-chip microwave communication devices. Those are also capable of forming magnonic minibands with allowed and forbidden frequencies [11][12][13]. By varying the physical and geometrical parameters of the artificial crystal, the nature of intra-element and inter-element magnetic field distributions within the array can be tuned, which in turn, modify its SW dynamics. A plethora of studies on the quasi-static and dynamic properties of 1-D, 2-D and 3-D MCs have been carried out due to their fundamental physical properties and their promising applications, such as spin-wave filter, coupler, phase shifter, splitter and other magnonic devices [14][15][16][17][18][19][20][21][22][23]. Recently, the entanglement between various spin-based phenomena has emerged as a new field, coined as magnon-spintronics [24]. Analogous to various natural or artificial crystals, introduction of bi-or multi-components can lead to a variation in the periodic potential ...
We report spin-wave excitations in annular antidot lattice fabricated from 15 nm-thin Ni 80 Fe 20 film. The nanodots of 170 nm diameters are embedded in the 350 nm (diameter) antidot lattice to form the annular antidot lattice, which is arranged in a square lattice with edge-to-edge separation of 120 nm. A strong anisotropy in the spin-wave modes are observed with the change in orientation angle (ϕ) of the in-plane bias magnetic field by using Time-resolved Magneto-optic Kerr microscope. A flattened four-fold rotational symmetry, mode hopping and mode conversion leading to mode quenching for three prominent spin-wave modes are observed in this lattice with the variation of the bias field orientation. Micromagnetic simulations enable us to successfully reproduce the measured evolution of frequencies with the orientation of bias magnetic field, as well as to identify the spatial profiles of the modes. The magnetostatic field analysis, suggest the existence of magnetostatic coupling between the dot and antidot in annular antidot sample. Further local excitations of some selective spin-wave modes using numerical simulations showed the anisotropic spin-wave propagation through the lattice.
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