Magneto-Optical Investigations of Tailored Exchange Biased Magnetoelectric Composites for Biomagnetic Field SensingThursday (08.06.2017) 15:40 - 16:00 Förde II Part of:
Magnetoelectric (ME) composites, based on piezoelectric and magnetostrictive materials, with their high ME coefficients are promising candidates for highly sensitive AC magnetic field sensors. In our work we apply various magnetic domain observation methods to obtain a broad understanding of magnetic noise contributions in our composites. ME measurements combined with advanced in operando domain observations give the opportunity to directly correlate magnetic domain activity to magnetic measurements and ME response. Here, the rarely used magneto-optical Voigt effect facilitates local magnetostriction maps and allows derivation of lateral ME response. We report on sputtered ME composites with AlN as the piezoelectric phase and multi-layered Fe70.2Co7.8Si12B10 as the magnetostrictive component. The later has a basic sequence of Ta/Cu/Mn70Ir30/FeCoSiB to set an exchange bias on the FeCoSiB layer.Varying the MnIr thickness allows us to align the exchange bias of individual magnetostrictive layer to achieve an antiparallel magnetization configuration. This topic is further researched in regards to the corresponding blocking temperatures, which is an important factor for achieving an antiparallel magnetization state in exchange biased layers by means of heat treatments. With the antiparallel state we achieve a narrower flux closure, which in return reduces the effect of the demagnetization field. Measurements show that spike domain formation in the system is reduced, if an antiparallel state is achieved instead of a parallel one. The change in domain formation is expected to reduce the magnetically induced noise in our sensor system. In another approach using a variation of the ferromagnetic (FM) layer thickness, the magnetic domain configuration and the overall magnetic behaviour of the magnetostrictive system can be tailored further. The previous mentioned characterization techniques also permit us to investigate the influence of edge profiles of the FM layer with respect to demagnetization fields and edge domains. An overview of the structural parameters that determine the magnetic domain behaviour and the resulting connection to the ME response will be given.