Functional nanostructures for bias-magnet-free and reconfigurable microwave magnetic devices

Recent demonstrations of the reconfigurable microwave properties based on patterned magnetic nanostructures without any external bias magnetic field have been reviewed. Two main design strategies for the nanostructures have been discussed. Firstly, self-biased nanomagnetic networks and multilayer structures that possess two different remanent magnetic states are exploited. Different remanent states are associated with distinct microwave properties and they are within a nanosecond time scale by using a simple field initialization scheme. The dipolar coupling field and the demagnetization field variations have been attributed to the origin of the tunable microwave responses. Secondly, magnetic skyrmions have been explored for tunable microwave properties. In this regard, skyrmion size which is directly related to its resonant modes has been controlled by placing it at different positions in an engineered nanostructure with varying edge repulsions. Finally, an outlook on the future directions and scopes of bias-free microwave devices have been discussed. It is also outlined that such devices have potential implications for the logic and magnonic technologies beyond their applications for microwave magnetic devices.