Domain-wall based magnetic nanosensors for metrology and bio applications

Orateur : Olga KAZAKOVA (National Physical Laboratory, Teddington, UK)

Dynamics of domain walls (DWs) in nanodevices made of soft magnetic materials has been proven to be reproducible and highly sensitive to external magnetic fields. We apply magnetotrasport measurements, magnetic imaging and micromagnetic modelling to study, analyse and predict evolution of magnetic DWs in various magnetic nanostructures with dimensions down to 50-nm wide. The complete range of angular dependent magnetotransport measurements is compiled into DW magnetoresistance state space maps. The analyses allows to determine the optimal working parameters, e.g. minimal switching field or maximal separation between the pinning/depinning fields. We propose that state space maps can be reliably used to initialise magnetic devices and predict their evolution in magnetic field, eliminating the need of electrical measurements We further investigate the effect of single magnetic bead (MB) on DW dynamics, in particular its influence on the change of the DW depinning field. To study the 3D sensitivity of DW nanosensors, we present magnetic scanning gate microscopy studies using a custom-made probe with an attached magnetic bead or nanoparticle. The MB–DW interaction is visualised by measuring changes in the electrical resistance of the device as a function of the tip position. By scanning at different heights, we create a 3D map of the MB–DW interaction and extract the sensing volume for different experimental parameters. The method provides a very effective, universal and non-destructive route to study MB–DW interactions, thus reducing cost of tests and speeding up the development and optimization of DW-based technology in biomedical and metrological applications.

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