  Micromagnetic sensors play a major role towards the miniaturization in the
industrial society. The adoption of new and emerging sensor technologies like
anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR) and tunnel
magnetoresistance (TMR) sensors are mainly driven by their integrability and
enhanced sensitivity. At the core of such sensors, a microstructured
ferromagnetic thin film element transduces the magnetic signal. Such elements
usually switch via multi-domain, C- or S-shaped magnetization states and,
therefore, often exhibit an open non-linear hysteresis curve. Linearity and
hysteretic effects, as well as magnetic noise are key features in the
improvement of such sensors. Here, we report on the physical origin of these
disturbing factors and the inherent connection of noise and hysteresis.
Critical noise sources are identified by means of analytic and micromagnetic
models. The dominant noise source is due to irreproducible magnetic switching
of the transducer element at external fields close to the Stoner Wohlfarth
switching field. Furthermore, a solution is presented to overcome these
limiting factors: a disruptive sensor design is proposed and analyzed which
realizes a topologically protected magnetic vortex state in the transducer
element. Compared to state of the art sensors the proposed sensor layout has
negligible hysteresis, a linear regime about an order of magnitude higher and
lower magnetic noise making the sensor ideal candidate for applications ranging
from automotive industry to biological application.
