Non Uniform Magnetization Dynamics of Antidot Arrays : Experimental and Numerical Investigations of Domain Patterns and Spin Waves

In this work, the static and dynamic magnetization behaviour of non-uniform magnetization distributions in single and antiferromagnetically coupled bi-layer Co40Fe40B20 films, which are patterned in a square array of circular antidots, is investigated. The static and dynamic magnetization configurations of the samples are recorded via static and time-resolved wide-field magnetooptical Kerr effect microscopy. The latter one as a unique technique allows for the detection of domain wall emitted magnetic and elastic waves. The dynamic magnetic behaviour is modelled numerically via micromagnetic simulations. The magnetic structure is exposed to a pulse and a harmonic sinusoidal field excitation. For the first case, a method is developed which is capable of mapping the spatial distributions of the local magnetic resonance frequencies fr,l. For the single layer structure, backward volume spin waves are detected. For the bi-layer structures, magnetization states with antiparallel aligned domains are investigated, which display a non-reciprocity of spin wave propagation as well as an asymmetric dispersion at low magnetic fields. It is shown how to enable a manipulation of the dispersion relation via the antiferromagnetic coupling and the anisotropy field. The frequency splitting in a low magnetic field and exhibited additional resonance frequencies can be used when an operation frequency higher than the natural resonance frequency of the material is required. It is further shown that domain walls in an antidot array can act as magnetic antennas while the shape and the propagation direction of the created waves are tunable via bias and uniaxial anisotropy fields, as well as frequency and amplitude of the excitation field. The layering of the magnetic structures and antiferromagnetic interlayer coupling give rise to an additional tunability.


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