Berlin 2018 – scientific programme

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MA: Fachverband Magnetismus

MA 26: Thin films – coupling effects

MA 26.4: Talk

Wednesday, March 14, 2018, 10:15–10:30, EB 301

Enhanced exchange bias in MnN/CoFe bilayers after high-temperature annealing — •Mareike Dunz, Jan Schmalhorst, and Markus Meinert — Center for Spinelectronic Materials and Devices, Physics Department, Bielefeld University, Germany

The exchange bias effect is crucial for pinning ferromagnetic electrodes in GMR or TMR devices. Recently, we found that optimized polycrystalline MnN/CoFe bilayer systems with t_MnN=30 nm show exchange bias of up to 1800 Oe at room temperature [1]. This makes antiferromagnetic Θ−MnN a promising alternative for expensive materials like MnIr.

Here, we report on even higher exchange bias that is observed in similar bilayers after annealing them at high temperatures around 500^∘C. For systems with t_MnN=48 nm, exchange bias of more than 2700 Oe is achieved. However, this is only observable for bilayers with thicknesses of MnN higher than 40 nm. To identify the origin of this behavior, X-ray diffraction and Auger depth profiling measurements were performed. They reveal a strong diffusion of nitrogen from the MnN into the Ta buffer layer of the samples. As thicker MnN layers have a better thermal stability due to their large nitrogen reservoir, they can tolerate the high annealing temperatures that induce the increase of exchange bias. Reversed field cooling experiments show that high-temperature annealing also yields an increased median blocking temperature of the MnN/CoFe system.
[1] M. Meinert et al., Phys. Rev. B 92(14), 144408 (2015)