Common GMR (giant magnetoresistance) /TMR (tunnel magnetoresistance) structures that are used e.g. in the field of data storage as read heads or MRAM (magnetic random access memory) devices consist of non-magnetostrictive materials in order to avoid any artefacts by external mechanical influences. GMR/TMR elements show a characteristic symmetrical behaviour in change of electrical resistance if an external magnetic field is applied. By replacing the non-magnetostrictive sensing layer by magnetostrictive material and using the inverse magnetostrictive effect such devices become sensitive towards mechanical strain and can be introduced as strain sensors [1, 2]. GMR and TMR structures have been developed consisting of one positive and one negative magnetostrictive sensing layer. This leads to a new characteristic resistance behaviour that depends on the alignment state of the magnetization of the two sensing layers, which is influenced by the applied external field and the level of mechanical stress. In correlation to the magneto electrical results to visualize magnetic domains of the sensing layer material under mechanical strain MOKE (magneto optical Kerr-effect) measurements will be presented. Additionally, the size dependency on these GMR/TMR structures will be discussed.

[1] Löhndorf, M.; Duenas-Lockwood, T.; Tewes, M.; Quandt; E., Rührig, R.; Wecker, J.: Highly sensitive strain sensors based on magnetic tunneling junctions (MTJs). Appl. Phys. Lett., 81 (2002), 313 – 315

[2] Löhndorf, M.; Dokupil, S.; Wecker, J.; Rührig, R.; Quandt; E.: Characterization of magnetic tunnel junctions (MTJ) with magnetostrictive free layer materials. J. Magn. Magn. Mater., 272–276 (2004), 2023–2024

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