Collective spin excitations in bicomponent magnonic crystals consisting of bilayer permalloy/Fe nanowires

Abstract

In the developing field of magnonics, it is very important to achieve tailoring of spin wave propagation by both a proper combination of materials with different magnetic properties and their nanostructuring on the submicrometric scale. With this in mind, we have exploited deep ultra-violet lithography, in combination with tilted shadow deposition technique, to fabricate arrays of closely spaced bi-layer nanowires (NWs), with separation d=100 nm and periodicity a=440 nm, having bottom and top layers made of Permalloy and Iron, respectively. The NWs have either "rectangular" cross section (bottom and upper layers of equal width) or "L-shaped" cross section (upper layer of half width). The frequency dispersion of collective spin wave excitations in the above bi-layered NWs arrays has been measured by the Brillouin light scattering technique while sweeping the wave vector perpendicularly to the wire length over three Brillouin zones of the reciprocal space. For the rectangular NWs, the lowest-frequency fundamental mode, characterized by a quasi-uniform profile of the amplitude of the dynamic magnetization across the NW width, exhibits a sizeable and periodic frequency dispersion. A similar dispersive mode is also present in L-shaped NWs, but the mode amplitude is concentrated in the thin side of the NWs. The width and the center frequency of the magnonic band associated with the above fundamental modes has been analysed, showing that both can be tuned by varying the external applied field. Moreover, for the L-shaped NWs it is shown that there is also a second dispersive mode, at higher frequency, characterized by an amplitude concentrated in the thick side of the NW. These experimental results have been quantitatively reproduced by an original numerical model that includes two-dimensional Green's 2 function of the dipole field of the dynamic magnetization and interlayer exchange coupling between the layers.

Reprogrammable magnonic band structure of layered permalloy/Cu/permalloy nanowires

“…It is noteworthy, that the two dispersive modes are not the lowest frequency ones as in the case of single-layer dense NW arrays, where only the lowest frequency mode exhibits a significant dispersion and higher frequency modes are dispersionless. [26] It is evident from Fig. 2(a) that the behavior of dispersive modes is quite different for the P and AP states with the same applied field H = + 150 Oe.…”

Magnetic Tunability of Permalloy Artificial Spin Ice Structures

“…The modification of static and dynamic magnetic properties as a function of size, shape, and distribution of magnetic dots [7][8][9] and antidots [10][11][12] has been studied extensively where the importance of configurational anisotropy was explained. Unlike dots with spherical symmetry, the structures with large aspect ratios such as nanowire (NW) can introduce shape anisotropy and, hence, play a significant role in engineering magnetic properties [13][14][15]. In addition, periodic width modulations in coupled NWs can act as reconfigurable magnonic crystals with spatial localization of magnon modes [16][17][18].…”

Spin-wave nonreciprocity and magnonic band structure in a thin permalloy film induced by dynamical coupling with an array of Ni stripes

“…In particular, by increasing the Fe thickness, one observes a substantial frequency increase, while the spatial profile of the mode gets narrowed and moves to the permalloy NW portion not covered by Fe. 31,32 The interesting questions arise which have not yet found answer. Firstly, does the regular pattern of the ferromagnetic substrate influence on the DE mode in homogeneous thin film to create magnonic band structure which is characteristic for MCs?…”