Microscopic Origin of Magnetization Reversal in Nanoscale Exchange-Coupled Ferri/Ferromagnetic Bilayers: Implications for High Energy Density Permanent Magnets and Spintronic Devices

Author(s)
Michael Heigl, Christoph Vogler, Andrada-Oana Mandru, Xue Zhao, Hans Josef Hug, Dieter Suess, Manfred Albrecht
Abstract

Giant exchange bias shifts of several Tesla have been reported in ferrimagnetic/ferromagnetic bilayer systems, which could be highly beneficial for contemporary high energy density permanent magnets and spintronic devices. However, the lack of microscopic studies of the reversal owing to the difficulty of measuring few nanometer-wide magnetic structures in high fields precludes the assessment of the lateral size of the inhomogeneity in relation to the intended application. In this study, the magnetic reversal process of nanoscale exchange-coupled bilayer systems, consisting of a ferrimagnetic TbFeCo alloy layer and a ferromagnetic [Co/Ni/Pt](N) multilayer, was investigated. In particular, minor loop measurements, probing solely on the reversal characteristics of the softer ferromagnetic layer, reveal two distinct reversal mechanisms, which depend critically on the thickness of the ferromagnetic layer. For thick layers, irreversible switching of the macroscopic minor loop is observed. The underlying microscopic origin of this reversal process was studied in detail by high-resolution magnetic force microscopy, showing that the reversal is triggered by in-plane domain walls propagating through the ferromagnetic layer. In contrast, thin ferromagnetic layers show a hysteresis-free reversal, which is nucleation-dominated due to grain-to-grain variations in magnetic anisotropy of the Co/Ni/Pt multilayer and an inhomogeneous exchange coupling with the magnetically hard TbFeCo layer, as confirmed by micromagnetic simulations.

Organisation(s)
Physics of Functional Materials
External organisation(s)
Universität Augsburg, Eidgenössische Materialprüfungs- und Forschungsanstalt, Universität Basel
Journal
ACS Applied Nano Materials
Volume
3
Pages
9218-9225
No. of pages
8
ISSN
2574-0970
DOI
https://doi.org/10.1021/acsanm.0c01835
Publication date
09-2020
Peer reviewed
Yes
Austrian Fields of Science 2012
210004 Nanomaterials, 102009 Computer simulation
Keywords
Portal url
https://ucris.univie.ac.at/portal/en/publications/microscopic-origin-of-magnetization-reversal-in-nanoscale-exchangecoupled-ferriferromagnetic-bilayers-implications-for-high-energy-density-permanent-magnets-and-spintronic-devices(e4310718-d859-4e48-a3ce-747cb0d26e24).html