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

Abstract

An efficient way for the control of spin wave propagation in a magnetic medium is the use of periodic patterns known as magnonic crystals (MCs). However, the fabrication of MCs especially bi-components, with periodicity on nanoscale, is a challenging task due to the requirement for sharp interfaces. An alternative method to circumvent this problem is to use homogeneous ferromagnetic film with modified periodically surrounding. The structure is also suitable for exploiting nonreciprocal properties of the surface spin waves. In this work, we demonstrate that the magnonic band structure forms in thin permalloy film due to dynamical magnetostatic coupling with Ni stripes near its surface. We show, that the band gap width can be systematically tuned by the changing interlayer thickness between film and stripes. We show also the effect of nonreciprocity, which is seen at the band gap edge shifted from the Brillouin zone boundary and also in nonreciprocal interaction of propagating spin waves in Py film with the standing spin waves in Ni stripes. Our findings open possibility for further investigation and exploitation of the nonreciprocity and band structure in magnonic devices.

Slow-Wave-Based Nanomagnonic Diode

“…Such a change of sign has also been predicted for films where breaking of the top-bottom magnetic symmetry is not obtained through a blockwise variation of M S , like here, but rather by a grading of saturation magnetization across the thickness [22]. In contrast, it has not been observed for bilayers where the two magnetic materials, being separated by a nonmagnetic spacer, are coupled only through longrange dipole interactions [41,42]. This further demonstrates the essential role played by short-range out-of-plane exchange coupling in this phenomenon.…”

Co- and contra-directional vertical coupling between ferromagnetic layers with grating for short-wavelength spin wave generation

“…It is manifested both, by a difference in the frequency of the waves at +k and −k, as well as the differences in the coupling strength on both sides of the Brillouin zone center. Clearly, hybridization at crossings for the −k are stronger than for the positive values of k. These effects are due to nonreciprocity of the Damon-Eshbach mode and the asymmetry of the structure [27,39].…”

“…Most of these studies deal with the in-plane SW propagation, but control of SW propagation in out of-plane direction is also promising for applications, although an area of 3D magnonics still remain unexplored [24]. Multilayer structures have already been studied for controlling SW spectra in thin films with using periodic gratings [25][26][27], periodic gratings were also used to excite and detect SWs propagating in homogeneous film beneath it. However, the way of transferring of the SW energy in the vertical direction has not yet been established.…”

Reflection-less width-modulated magnonic crystal

“…Magnonic crystals are produced using different types of magnetic materials: metals such as Ni and Co 28,29 , alloys such as Permalloy (Ni 80 Fe 20 ) 28,[30][31][32][33] and CoFeB 34,35 , Heusler compounds such as Co 2 ðFe 0:4 Mn 0:6 ÞSi 36,37 , and dielectrics like yttrium iron garnet (YIG, Y 3 Fe 5 O 12 ) 11,16,18,[20][21][22][23][24][25][26][27]38,39 . The main advantages in choosing μm-thick single-crystal YIG films over nm-thick metallic materials such as Permalloy or CoFeB is the small magnetic damping 40 and higher group velocity of dipolar SWs.…”