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A tunnel magnetoresistance (TMR) sensor based on magnetic tunnel junctions (MTJs) is a highly sensitive magnetic sensor workable at room temperature. Due to the dramatic increase in sensitivity achieved in recent years, the developed TMR sensors have succeed in measuring a bio-magnetic fields. The sensitivity of TMR sensors is determined from the slope of the magnetoresistance curve around zero magnetic field, thus both high TMR ratio and small magneto-crystalline anisotropy are required. In order to improve the sensitivity of TMR sensors, we have focused on Co-based Heusler alloy Co₂FeAl_xSi_1–x as a free layer in TMR sensor. This is because MTJs with Co₂FeAl_xSi_1–x electrode is promising for gaining a high TMR ratio due to its half-metallicity. On the other hand, their magneto-crystalline anisotropy has not been investigated so far. In this study, we have fabricated monocrystalline Co-based Heusler alloy Co₂FeAl_xSi_1–x thin films by co-sputtering method. Systematic investigation of their atomic ordering and magneto-crystalline anisotropy K₁ as a function of the Al component x was performed. Thickness of studied layers was kept constant as 50 nm. Magneto-crystalline anisotropy constant K₁ changed from positive to negative with increase of x, and it was almost zero around x = 0.33. At the same time for this composition, B2 ordering parameter was 0.7 and L2₁ ordering parameter was 0.3. These results are indicating that Co₂FeAl_xSi_1–x thin film with around x = 0.33 possesses both half-metallicity and small magneto-crystalline anisotropy K₁ so it can be ideal candidate to be used as a free layer in highly sensitive TMR sensors.

Wykład będzie prowadzony w języku angielskim w sali 203, dostępna będzie również transmisja ZOOM.

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