Dresden 2017 – scientific programme

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MA: Fachverband Magnetismus

MA 27: Spintronics (incl. Quantum Dynamics)

MA 27.7: Talk

Tuesday, March 21, 2017, 15:30–15:45, HSZ 301

Shape Memory Alloys in Hybrid Spintronic Devices — •Andreas Becker and Andreas Hütten — Bielefeld University, Bielefeld, Germany

Observations of the phase transition in ferromagnetic shape memory alloys (FSMAs) by x-ray diffraction and magnetization measurements are reported frequently. Our goal is to investigate the phase transformation by using the tunnel magnetoresistance effect (TMR), thus FSMAs are utilized either as ferromagnetic electrodes (Ni50-xCoxMn30Al20/MgO/ Co40Fe40B20) or as an underlying layer beneath the magnetic tunnel junction (Ni50-xCoxMn30Al20/ Co40Fe40B20/MgO/ Co40Fe40B20).

The off-stoichiometric Ni50-xCoxMn30Al20 thin films are grown by sputter deposition and patterned by e-beam lithography. X-ray diffraction measurements indicate a B2 crystal structure. An untypical change in the TMR amplitude is observed in tunnel junctions on top of the Heusler alloy upon heating the sample. We suggest that this phenomenon arises from the induced strain of the reverse martensitic transformation. Furthermore the FSMA will act as a ferromagnetic electrode if the magnetic properties are enhanced by substituting Ni with Co atoms. At x=10 a TMR of about 2.5% at room temperature and 6% at 10 K is measured in Ni50-xCoxMn30Al20 /MgO/Co40Fe40B20 tunnel junctions while no TMR is found over the measured temperature range in samples with x=4.