Generation of imprinted strain gradients for spintronics

[EN]In this work, we propose and evaluate an inexpensive and CMOS-compatible method to locally apply strain on a Si/SiOx substrate. Due to high growth temperatures and different thermal expansion coefficients, a SiN passivation layer exerts a compressive stress when deposited on a commercial silicon wafer. Removing selected areas of the passivation layer alters the strain on the micrometer range, leading to changes in the local magnetic anisotropy of a magnetic material through magnetoelastic interactions. Using Kerr microscopy, we experimentally demonstrate how the magnetoelastic energy landscape, created by a pair of openings, enables in a magnetic nanowire the creation of pinning sites for in-plane vortex walls that propagate in a magnetic racetrack. We report substantial pinning fields up to 15 mT for device-relevant ferromagnetic materials with positive magnetostriction. We support our experimental results with finite element simulations for the induced strain, micromagnetic simulations, and 1D model calculations using the realistic strain profile to identify the depinning mechanism. All the observations above are due to the magnetoelastic energy contribution in the system, which creates local energy minima for the domain wall at the desired location. By controlling domain walls with strain, we realize the prototype of a true power-on magnetic sensor that can measure discrete magnetic fields or Oersted currents. This utilizes a technology that does not require piezoelectric substrates or high-resolution lithography, thus enabling wafer-level production.This project has received funding from the European Union’s Horizon 2020 Research and Innovation Program under the Marie Skłodowska-Curie Grant Agreement No. 860060 “Magnetism and the effect of Electric Field” (MagnEFi), the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)— TRR 173-268565370 (Project Nos. A01 and B02), the DFG Funded Collaborative Research Center (CRC)1261/project A10, and the Austrian Research Promotion Agency (FFG). The work by L. L. Diaz and E. Martinez was partially supported via Project No. PID2020117024GB-C41 funded by Ministerio de Ciencia e Innovacion from the Spanish Government and from Consejeria de Educacion of Junta de Castilla y Le on via Project No. SA114P20. The authors also acknowledge support by the chip production facilities of Sensitec GmbH (Mainz, DE), where a part of this work was carried out, and the Max Planck Graduate Centre with Johannes Gutenberg University