Volume 78, Number 6, June 2007
Article Number 67002
Number of page(s) 4
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
Published online 25 May 2007
EPL, 78 (2007) 67002
DOI: 10.1209/0295-5075/78/67002

Strong temperature dependence of antiferromagnetic coupling in CoFeB/Ru/CoFeB

N. Wiese1, 2, T. Dimopoulos1, M. Rührig1, J. Wecker1, G. Reiss2, J. Sort3 and J. Nogués3

1  Siemens AG Corporate Technology - Paul-Gossen-Straße 100, 91052 Erlangen, Germany
2  University of Bielefeld, Nano Device Group - Universitätsstraße 25, 33615 Bielefeld, Germany
3  Institució Catalana de Recerca i Estudis Avançats (ICREA) and Departament de Física, Universitat Autònoma de Barcelona - 08193 Bellaterra, Spain

received 22 April 2007; accepted in final form 4 May 2007; published June 2007
published online 25 May 2007

The temperature dependence of saturation and spin-flop fields for artificial ferrimagnets (AFi) based on antiparallel coupled CoFeB/Ru/CoFeB trilayers has been investigated in a temperature range between 80 K and 600 K. The results presented in this paper are relevant for magnetic devices using this system, e.g. magnetic-random access memory based on spin-flop switching. In good accordance to the theory, the saturation field $H_{{\rm sat}}$ behaves like $H_{{\rm sat}} \propto H_{0} (T/T_{0})/{\rm sinh}(T/T_{0})$ with a characteristic temperature of $T_{0} \approx 150\,{\rm K}$. Within this model, the Fermi velocity for the Ru layer is of the order of $10^{5}\,{\rm m/s}$, therefore, explaining the strong variation of the coupling strength with the temperature in Ru-based AFi. Furthermore, a strong uniaxial anisotropy of $K_{{\rm u}}=2\times 10^{3}\,{\rm J/m}^{3}$ with a small angular distribution of the anisotropy axes is observed for the AFi trilayers based on amorphous CoFeB alloys.

75.70.-i - Magnetic properties of thin films, surfaces, and interfaces.
75.50.Kj - Amorphous and quasicrystalline magnetic materials.
75.30.Gw - Magnetic anisotropy.

© Europhysics Letters Association 2007