Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 25: Phase Transitions

O 25.5: Vortrag

Dienstag, 27. März 2007, 12:15–12:30, H41

Reversible martensitic phase transition in 4 ML Fe films on Cu(100): A variable temperature STM study — •Albert Biedermann — Institute of Materials Physics, University of Vienna, 1090 Vienna, Austria

In recent years it has been established that 3–4 ML Fe films grown on Cu(100) show a bcc-like structure in terms of crystallography (“nano-martensite”)[1] and electronic structure [2]. This work addresses the question whether there also exists a reversible martensitic phase transition between this bcc-like and the fcc phase. Temperature dependent LEED and SMOKE data by Zharnikov et al. [3] suggest a transformation from the ferromagnetic phase to the fcc phase in 4 ML films between 250 and 330 K and a slow reverse transformation after cooling to below 180 K. Indeed, variable temperature STM images obtained in the present experiments show a transition from the bcc-like to the fcc phase between 280 and 330 K in 4 ML films. The reverse transition occurs around 200–250 K on the slow time scale of the VT-STM experiment. This reversible martensitic transition confirms the rather strict correlation between bcc-like structure and ferromagnetic ordering in 4 ML films. The temperature dependent growth of the 2D martensitic “grains” and their characteristic length scales will be discussed.

[1] A. Biedermann, R. Tscheliessnig, M. Schmid, P. Varga, Phys. Rev. Lett. 87 (2001) 086103

[2] D. Spisak, J. Hafner, Phys. Rev. Lett. 88 (2002) 056101

[3] M. Zharnikov, A. Dittschar, W. Kuch, C. M. Schneider, and J. Kirschner, Phys. Rev. Lett. 76 (1996) 4620