Jeffrey McCord1
Kiel University1
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 magnetic applications in IoT, 5G, smartphones, energy, and biomedical engineering. In this context, dedicated research is currently being carried out on novel thin film magnetoelectric (ME) sensor concepts for the detection of magnetic fields down to the picotesla range.<br/><br/>Advanced wide-field magneto-optical Kerr effect microscopy [1] with high temporal resolution is used to study local effects in operating ME composite sensor structures. The realized magnetospatial analysis of working devices sheds light on magnetization changes due to domain nucleation, domain wall resonances, domain wall bending modes, precessional magnetization effects and spin-wave-like phenomena. Each of these is specific to different types of composite ME sensors, ranging from resonance to modulated to DE to SAW sensor systems. Complementary ME response, noise and detection limit analyses reveal the different magnetic noise mechanisms with different magnetic domain activities for the different sensor types (e.g. [2-5]). By understanding the complex magnetic interactions, strategies and implementations are identified to optimize sensor structures. Single magnetic domain layers are the basis for low noise magnetic thin film sensors due to the absence of magnetic domain walls.<br/><br/>The design and application of magnetic layered structures with minimal noise performance sensitivity is discussed. Beyond magnetic domain engineering [6], other schemes of magnetic noise suppression, based on a combination of sensing and pinning magnetic multilayer stacks are discussed. By introducing magnetic sensing layers with subtractive response to carrier excitations while maintaining sensitivity, the influence of the electrical carrier signal to noise is virtually eliminated [7]. 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. Fundamental limitations of composite ME sensors beyond magnetic domain activity will be further discussed [5].<br/><br/>Funding by the DFG for the CRC 1261 “Magnetoelectric Sensors: From Composite Materials to Biomagnetic Diagnostics” and collaborations within the CRC are acknowledged.<br/><br/><b>References</b><br/>[1] J. McCord, Journal of Physics D: Applied Physics 48, 333001, 2015.<br/>[2] N. O. Urs, I. Teliban, A. Piorra, et al., Applied Physics Letters 105, 202406, 2014.<br/>[3] N.O. Urs, E. Golubeva, V. Röbisch, et al., Physical Review Applied 13, 024018, 2020.<br/>[4] C. Müller, P. Durdaut, R.B. Holländer, et al., Advanced Electronic Materials, 2200033, 2022.<br/>[5] E. Spetzler, B. Spetzler, J. McCord, under review.<br/>[6] M. Jovičević Klug, L. Thormählen, V. Röbisch, et al., Applied Physics Letters 114, 192410, 2019.<br/>[7] D. Seidler, P. Hayes, E. Spetzler, et al., in preparation.