Strain-resistance effect of metallic sensor layers in the antiferromagnetic state
Final Report Abstract
Sensors for measuring pressures, forces and strains are based on the conversion of mechanical quantities into electrical signals. Among the many physical effects that enable conversion, this project investigates the relatively unknown strain-resistance effect of antiferromagnetic metal layers with regard to possible sensor applications. The focus is on specific properties such as high strain sensitivity, low temperature coefficient of resistance (TCR), high resistance stability and maximum application temperatures. For films containing chromium, the project builds on previous work with Cr and Cr-N films and investigates the influence of alloying elements with low concentrations. In addition, the strain-resistance effect of manganese compounds, which are also of particular interest in the field of antiferromagnetic spintronics, is being investigated. Sputter-deposited thin films of pure chromium and chromium-rich alloys are evaluated in terms of electrical resistivity and piezoresistivity, as measured by the gauge factor, from room temperature to 470°C. The alloying elements are manganese, platinum, vanadium and tungsten, which are known to either stabilize or destabilize the spin-density-wave antiferromagnetism found in Cr. In concentration series and a substrate bias voltage series the variation of resistivity, gauge factors (of up to 20) and their temperature coefficients are shown. High-temperature resistivity measurements indicate increased Néel transition temperatures that are related to a gauge factor maximum. Generally, the gauge factor increases towards the Néel temperature. The Cr60Mn40 film, however, has a small negative temperature coefficient of the gauge factor. This is a desired property in strain and pressure sensor films, as it allows compensating the temperature coefficient of the elastic modulus of aluminum or steel transducers. An analysis of the resistance change through mechanical loading quantifies small Néel temperature changes of several Kelvin per permille of strain that are likely the mechanism of the observed piezoresistivity. Overall, the Cr-rich alloy thin films represent a class of metallic piezoresistive films with properties that can be well adjusted to the sensor application by concentration and sputtering parameters. In contrast to the Cr-rich coatings, only very low strain-resistance effects can be measured for the manganese-based thin films. Only the Mn- Ru alloy shows a higher effect, but its stability is unsatisfactory.
Publications
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Spannende physikalische Effekte für die Sensorik am Beispiel eines Dissertationsprojektes; Hochschulzeitschrift sichtbar (Ausgabe 2/2021, S. 54–58)
Schwebke, Silvan & Schultes, Günter
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Antiferromagnetic chromium thin films as piezoresistive sensor materials. Journal of Applied Physics, 132(18).
Schwebke, S. & Schultes, G.
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E-MRS 2022 Spring Meeting (Symposium O, code O.3.20): Another class of piezoresistive thin film materials: Antiferromagnetic chromium alloys
Silvan Schwebke & Günter Schultes
