Dresden 2017 – scientific programme
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MA: Fachverband Magnetismus
MA 66: Poster 3
MA 66.3: Poster
Friday, March 24, 2017, 09:30–13:00, P2-OG2
Exchange bias in chemically disordered Mn0.8N0.2/CoFe systems — Simon Tilleke, •Katharina Fritz, Björn Büker, and Markus Meinert — Center for Spinelectronic Materials and Devices, Physics Department, Bielefeld University, Germany
In a recent publication [1], we reported on large exchange bias obtained in Ta/Θ-MnN/CoFe stacks at room temperature. In search for Mn-N phases with higher anisotropy energy, we investigated Mn-N films with lower nitrogen content to obtain other antiferromagnetic Mn-N phases, such as η-Mn3N2 or ζ-Mn2N with the same deposition process.
We found an antiferromagnetic phase at the composition Mn0.8N0.2 that allows for large exchange bias with an interfacial exchange energy of Js = 0.39 mJ/m2 (similar to Θ-MnN/CoFe), but with a significantly reduced critical thickness of the antiferromagnet and thus a higher magnetocrystalline anisotropy energy. X-ray diffraction identifies the Mn0.8N0.2 as a simple, chemically disordered fcc structure with no traces of an ordered є-Mn4N structure in the as-deposited state. Annealing at temperatures above 150 ∘C will, however, induce chemical ordering of the Mn and N atoms and a transformation into well-ordered є-Mn4N is completed at annealing temperatures above 200 ∘C. After the transformation, no exchange bias is detected, in line with the ferrimagnetic ground state of the є-Mn4N phase. Exchange bias up to 1400 Oe is obtained at room temperature at a Mn0.8N0.2-thickness of 20 nm.
[1] M. Meinert et al., Phys. Rev. B 92, 144408 (2015)