Berlin 2008 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 19: SYM Thin Film Magnetic Materials: Microstructure, Reaction and Magnetic Coupling II
MM 19.2: Invited Talk
Tuesday, February 26, 2008, 12:00–12:30, H 0107
Thermal stability and reaction of GMR sensor materials — •Vitaliy Vovk1, Constantin Ene2, and Guido Schmitz3 — 1Department of materials, University of Oxford, Parks Road 3PH, U.K. — 2Institut für Materialphysik, Univ. Goettingen, Friedrich-Hundt-Platz 1, 37077 Göttingen, Germany — 3Institut für Materialphysik, WWU Muenster, Wilhelm-Klemm-Str. 10, 48149 Muenster, Germany
State-of-the-art GMR sensors usually consist of thin film multilayers with a periodicity of a few nanometers only. The significant contribution of interfaces makes these nano-scaled materials inherently unstable. In the talk, the stability and thermal reaction of Py/Cu (Py stands for Ni81Fe19) and Co/Cu magneto resistive systems is addressed.
Thin film multilayers are analysed by wide angle atom probe tomography (WATAP). The different thermodynamics of the studied systems causes different mechanisms of GMR degradation. In the Py/Cu system, GMR deterioration occurs due to short range mixing at the layer interfaces, caused by gradient energies and quantitatively described by Cahn-Hilliard theory. In contrast, this mechanism is not observed in Co/Cu multilayers up to temperatures of 450°C. Instead, ferromagnetic bridges along grain boundaries through Cu appear at even higher temperatures.
Besides the mixing reaction, a recrystallization transforming the layer texture is observed in both metallic systems. Elasto-mechanic calculations demonstrate that this transformation is due to elastic anisotropy.