Many modern technological applications are based on magnetic forces. Examples are moving components in electric vehicles and storing data on hard disks. Magnetic fields are also used as sensors to detect other magnetic fields. In the automotive industry, for example, more precise magnetic field sensors are used in ABS systems.
The use of new magnetoresistive sensor technologies, such as anisotropic magnetoresistance, giant magnetoresistance, and tunnel magnetoresistance, is being driven by their increased sensitivity and improved integration capability.
The core of novel magnetic field sensors is a microstructured, ferromagnetic, thin-film element that can convert magnetic signals. This so-called transducer element changes its electrical behavior as soon as a magnetic field is applied from the outside. The atomic "compass needles," the atomic magnetic dipoles, are realigned and thus change the electrical resistance of the transducer element. This behavior is used to determine the magnetic fields.
However, the performance of these sensors is considerably limited by a number of factors. The physical origin and fundamental limits have been analyzed in detail by a team led by Dieter Süss in a cooperation between the University of Vienna, the Danube University Krems, and Infineon AG in the framework of the Christian Doppler Laboratory "Advanced Magnetic Sensing and Materials." They recently published the results of their investigations and concrete proposals for solutions.
By means of computer simulations that have been validated by experiments, the scientists showed that both interference signals, magnetic noise, and hysteresis can be significantly reduced by redesigning the transducer element. In the new design, the atomic magnetic dipoles of the transducer element are aligned in a circle around a center, similar to a hurricane. An externally applied magnetic field changes the position of the center of this vortex, which in turn leads directly to a change in the electrical resistance.
"This development shows the first mass application of magnetic vortex structures and a significant improvement over conventional magnetic sensors," says Süss.