Magnetoresistive sensors based on giant magnetoresistance (GMR) or tunnel magnetoresistance (TMR) play a major role towards the miniaturization in the industrial society. Typically, spin-valve-type magnetoresistive sensors are embedded in a Wheatstone bridge configuration with rectangular, meander-like or elliptically shaped thin film elements. 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 are key features in the improvement of such sensors.
We will present a different approach by using circularly shaped elements exhibiting a different magnetization state of a magnetic vortex . This is one of the fundamental magnetization ground states occurring in disk-shaped thin film elements and is characterized by minimization of the demagnetizing energy at the expense of exchange energy.
Experimental data were generated on electrically contacted GMR and TMR disks which were fabricated by optical lithography. The following advantages will be discussed and compared to standard elliptical sensor elements. (a) The vortex state shows essentially no hysteresis in the minor loop. (b) Since the vortex nucleation happens prior to the zero field, the M(H=0)=0 crossing is independent of history. (c) The critical fields can be easily controlled by the element geometry. (d) The noise is low.
All characteristic experimental values have been determined in dependence of free layer thickness, disk diameter and temperature. These findings are discussed in the frame of the semi-analytical rigid-vortex-model  and micromagnetic simulations.
The financial support by the Austrian Federal Ministry of Science, Research and Economy and the Christian Doppler Research Association in Austria is gratefully acknowledged.
 D. Suess, A. Bachleitner-Hofmann, A. Satz, H. Weitensfelder, C. Vogler, F. Bruckner, C. Abert, K. Prügl, J. Zimmer, C. Huber, S. Luber, W. Raberg, T. Schrefl, H. Brückl, „Topologically Protected Vortex Structures to Realize Low-Noise Magnetic Sensors with High Linear Range”, Nature Electronics 1, 362 (2018)
 K. Y. Guslienko et al., “Magnetization reversal due to vortex nucleation, displacement, and annihilation in submicron ferromagnetic dot arrays”, Phys. Rev. B 65 (2001)
A novel technique to realize large quantities of stacked multifunctional anisotropic nanoparticles with narrow size distribution is presented. Through the combination of Ultraviolet Nano-Imprint Lithography (UV-NIL), physical vapor deposition and subsequent lift-off processes we fabricate and disperse these particles in solution for the use in biomolecular sensing applications. Compared to chemical nanoparticle synthesis our approach holds several advantages. First, one can control the nanoparticle shape by choosing an appropriate nanopattern for the UV-NIL process. Second, we can choose the composition of the nanoparticles as the materials are deposited layer-wise by sputter deposition. Third, we can fabricate nanoparticles with very small geometrical variations. This is in contrast to chemical synthesis methods where the layer thicknesses and particle size distribution are harder to control.
In this manuscript, a technique to realize multifunctional anisotropic nanoparticles with small size distribution in large quantities is presented. The fabrication of the nanoparticles is based on Ultraviolet Nanoimprint Lithography (UV-NIL), physical vapor deposition and lift-off processes in order to finally disperse the nanoparticles in solution. The particles are designed for in-vitro biomolecular diagnostics. The underlying homogeneous biomolecular sensing method is based on the optical detection of changes in the rotational dynamics of anisotropic hybrid nanoparticles immersed in the sample solution, such as blood. ,  This approach requires highly monodisperse nanoparticles in order to achieve a high sensitivity in molecule detection. The fabrication method based on UV-NIL and lift-off processes holds several advantages compared to chemical synthesized nanoparticles, like very small size variations and engineering freedom in particle geometry. We demonstrate the fabrication of elliptical particles with an area size of 1,557 × 10^(-12)m2 ±3%.