Effects of field annealing on MnN/CoFeB exchange bias systems

ORAL

Abstract

Antiferromagnets are commonly used in magnetic tunnel junction based spintronics to fix the ferromagnetic reference layer using the exchange bias effect. The antiferromagnetic MnN Θ-phase exhibits large exchange bias fields on CoFe films on order of 1800 Oe which can be enhanced with increased annealing temperature [1,2]. The exchange bias field in MnN/CoFeB systems is observed to be dependent on annealing temperature and MnN thickness. The effect of annealing temperature (as-deposited, 325 and 525 C) and MnN thickness (30 and 48 nm) on the magnetic and structural properties of MnN/CoFeB samples have been examined with polarized neutron reflectivity (PNR), x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). PNR fits show that nitrogen increasingly diffuses from MnN to the underlying seed layer as the annealing temperature increases, which leads to a disappearance of the exchange bias effect when the MnN thickness is not sufficient. Intermixing of Mn, Fe, and Co at the MnN/CoFeB interface is also observed in PNR, XAS and XMCD measurements and is correlated to observed changes in magnetization.

[1] M. Meinert, B. Büker, D. Graulich,and M. Dunz, Phys. Rev. B. 92, 144408 (2015)
[2] M. Dunz, J. Schmalhorst, and M. Meinert, AIP Adv. 8 056304 (2018)

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Presenters

  • Patrick Quarterman

    National Institute of Standards and Technology, University of Minnesota

Authors

  • Patrick Quarterman

    National Institute of Standards and Technology, University of Minnesota

  • Ingrid Hallsteinsen

    Lawrence Berkeley National Laboratory

  • Mareike Dunz

    Center for Spinelectronic Materials and Devices, Faculty of Physics, Bielefeld University, D-33615 Bielefeld, Germany

  • Alexander Grutter

    National Institute of Standards and Technology, NIST, NIST Center for Neutron Research, NIST Gaithersburg, Neutron-Condensed Matter Science Group, NIST, NIST Center for Neutron Research

  • Markus Meinert

    Center for Spinelectronic Materials and Devices, Faculty of Physics, Bielefeld University, D-33615 Bielefeld, Germany

  • Elke Arenholz

    Advanced Light Source, Lawrence Berkeley National Laboratory, Lawrence Berkeley National Laboratory, Advanced Light Source

  • Julie Borchers

    National Institute of Standards and Technology, NIST Center for Neutron Research, National Institute of Standards and Technology