Brillouin Light Scattering Study Of Spin Waves Nonreciprocity In Magnetic Thin Films

Spin waves are waves formed by the transfer of electron spin precession states.The nonreciprocity of spin wave propagation(ie,the amplitude and/or frequency varies with the direction of propagation)is the key to the realization of spin wave logic devices.Therefore,the study of spin wave nonreciprocity and the regulation of nonreciprocity has become a hot research topic.Dipole interactions can induce nonreciprocity in the spatial distribution of spin wave intensity in thicker magnetic films;dipole interactions are weaker in ultrathin films,at this time,in asymmetric structures,DzyaloshinskiiMoriya interactions(DMI)can induce strong spin wave nonreciprocity.We use Brillouin light scattering(BLS)to study spin wave nonreciprocity caused by DMI and interlayer dipole interactions,respectively,and realize the regulation of nonreciprocity.The following innovative conclusions are drawn:1.In Co/Pt bilayers,the spin wave nonreciprocal temperature dependence induced by DMI dominated by spin orbit coupling at the heavy metal/ferromagnetic interface was investigated using BLS.With the increase of temperature,the DMI increases obviously,and the nonreciprocity of the spin wave dispersion also increases,and the spin wave nonreciprocity is adjusted in a wide range by changing the temperature.Analysis of experimental data revealed that the temperature dependence of DMI may be related to thermal disorder,lattice expansion,and material strain.2.In Pt(110)/Co Fe B(211)bilayers,due to the dual crystal symmetry at the system interface,the band alignment and orbital hybridization around the Fermi level are different along two orthogonal directions,which can generate anisotropy DMI.The DMI intensity in the Pt[001] direction is 2.6 times that in the Pt[11(?)0] direction.This DMI anisotropy results in spin wave nonreciprocal anisotropy,and the spin wave frequency difference at opposite wavevectors caused by spin wave nonreciprocity up to1.51 GHz at large wavevectors,which can be achieved by Co Fe B Thickness modulates the degree of nonreciprocity and anisotropy.3.In the Co/Ru/Co Fe B three-layer film,the spin wave nonreciprocity caused by the interlayer dipole interaction is studied.Dipole interactions act differently on spin wave modes that precess in phase versus antiphase.Finally,the coupling between the acoustic branch and the optical branch spin wave is studied,and the coupling phenomenon can be controlled in a wide range by changing the thickness of the Ru layer and the size of the wave vector.