Speaker
Description
Magnetic field sensors are devices that detect and measure magnetic fields around permanent magnets, electrical conductors, and electrical devices. As such, they are particularly relevant for applications in IoT, 5G, smartphones, energy, and biomedical engineering. In this context, dedicated research is being carried out on novel thin film composite magnetoelectric (ME) sensor concepts for the detection of magnetic fields down to the picotesla range. Advanced wide-field magneto-optical Kerr effect microscopy with high temporal resolution is used to study local effects in operating ME composite sensor structures. Together with supporting electrical measurements, the realized magnetospatial analysis of working devices sheds light on magnetization changes due to domain nucleation, domain wall resonances, domain wall bending modes, and spin-wave-like phenomena. Each of these is specific to different types of composite ME sensors, ranging from resonance to modulated to $\Delta E$ to SAW sensor systems. Complementary electrical noise and detection limit analyses reveal the different noise mechanisms, electrical and magnetic, for the different sensors. By understanding the complex magnetic interactions, strategies and implementations are identified to optimize magnetic sensor structures.
The design and application of flux closing magnetic multilayer structures with minimal noise is discussed. Magnetostatically stabilized but still responsive single magnetic domain layers are the basis for low noise sensors due to the absence of magnetic domain walls. Limits for sensitivity enhancement from additional magnetoelastic domain effects will be discussed. Beyond magnetic domain engineering, other schemes of magnetic noise suppression, based on a combination of sensing and pinning magnetic multilayer stacks are demonstrated. By introducing special magnetic sensing layers the influence of the electrical carrier signal to noise is virtually eliminated. The magnetically enforced reduction of the electrical background signal paves the way for ultra-low noise ME sensor applications capable of detecting picotesla magnetic fields. We show that with the current approaches and beyond magnetic domain activity, we are seeing novel effects based on non-linear magnetoelastic effects. Low noise sensor detectabilities are now approaching fundamental limits.
Acknowledgements
Funding by the DFG for the CRC 1261 “Magnetoelectric Sensors: From Composite Materials to Biomagnetic Diagnostics” is highly acknowledged.
References
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