Magnetic sensors play a key role in a variety of applications, such as speed and position sensing in the automotive industry and in biomedical applications. The Christian Doppler Laboratory, “Advanced Magnetic Sensing and Materials,” headed by Dieter Süss, in a collaboration among the University of Vienna, the Danube University Krems, and Infineon AG, has developed novel magnetic sensors that surpass conventional technologies in performance and accuracy The researchers present the new development in the latest issue of the journal Nature Electronics.

Many modern technological applications are based on magnetic forces, for example to move components in electric vehicles or to store data on hard disks. Magnetic fields are also used as sensors to detect other magnetic fields. The total market for magnetic field sensors based on semiconductor technology currently amounts to USD 1,670 million and continues to grow. In the automotive industry, for example, precise magnetic field sensors are used in ABS systems to detect tire pressure. This eliminates the need for additional pressure sensors in the tires and saves resources and cost. The use of new magnetoresistive sensor technologies such as anisotropic magnetoresistance, giant magnetoresistance, and tunnel magnetoresistance, is driven primarily by their increased sensitivity and improved integration capability.

A magnetic sensor in which the magnetic transducer element has a vortex state. (Image courtesy of Dieter Süss et al.)

The core of these novel magnetic field sensors is a microstructured ferromagnetic thin-film element that can react to 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 the sensors is considerably limited by a number of factors. Their physical origin and fundamental limits have been analyzed in detail by the team. They recently published the results of their investigations and concrete proposals for solutions in the journal Nature Electronics.

By means of computer simulations that have been validated by experiments, the scientists showed that 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 is a significant improvement over conventional magnetic sensors according to the researchers.

The project is an example of basic research and purely scientific questions, such as the behavior of magnetic vortex structures in external magnetic fields, leading to successful applications. In this collaboration between science and industry, industry provided practical relevant questions as well as the technical facilities, such as clean rooms, for the realization of these complex technologies.

For more information, see Nature Electronics (2018), DOI: 10.1038/s41928-018-0084-2.