Ferromagnetic resonance in Ni—Mn-Ga thin films and thin-film tubes

Janusz Dubowik 1Iwona Goscianska 2Yuri Kudryavtsev 3

1. Polish Academy of Sciences, Institute of Molecular Physics, Mariana Smoluchowskiego 17, Poznań 60-179, Poland
2. Adam Mickiewicz University, Department of Physics, Umultowska 85, Poznań 61-614, Poland
3. G.V. Kurdyumov Institute for Metal Physics National Academy of Sciences (IMP), Vernadsky Blvd. 36, Kyiv UA03680, Ukraine

Abstract

Ferromagnetic resonance (FMR) has been proven to be useful tool to determine magnetic properties of thin films. The FMR data (the resonance fields and linewidth) for thin films enable evaluation of their effective magnetization, magnetic anisotropies, and their homogeneity and relaxation mechanisms. Usually the films are firmly fixed onto substrates and thus suffer a huge stress – tensile or compressive. We report on FMR experiments performed for the first time on thin (100 nm) Ni-Mn-Ga films clamped to the mica substrates and then fully released from them. The aim is to evaluate the role of magnetoelastic coupling in stressed Ni-Mn-Ga Heusler alloy films that undergo martensitic transformation. The as-deposited films are usually under stress and they form curled thin-film tubes after releasing from the substrates. We will discuss and compare the resonance conditions for metallic films and, in particular, for thin-film tubes and explain a peculiar FMR response in thin-film tubes as resulting both from a small microwave penetration depth and a specific angular dependence of the FMR linewidth in thin films. The temperature dependencies of the resonance field in the Ni-Mn-Ga films and thin-film tubes are measured in a wide temperature range of 78 – 400 K. The martensitic transformation is shown to occur in a range of 220 – 300 K. The experimental results show that the difference in the effective magnetization 4pi(Meff tubes-Meff films) is negligible in austenite phase and it increases to about 1 – 1.5 kG at temperatures well below the martensitic transformation. The data suggests that magnetoelastic coupling in the martensite phase of Ni-Mn-Ga thin films is typical of normal thin magnetic films with magnetostriction of about 50 ppm. The results will be compared with the FMR data obtained on Ni thin films and Ni thin-film tubes.

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Presentation: Poster at E-MRS Fall Meeting 2007, Symposium E, by Janusz Dubowik
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-07 08:12
Revised:   2009-06-07 00:44
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