Dresden 2006 – wissenschaftliches Programm

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DS: Dünne Schichten

DS 8: Functional thin films I

DS 8.3: Vortrag

Dienstag, 28. März 2006, 10:30–10:45, GER 37

Phase stability and epitaxial growth of NiMn-based magnetic shape memory thin films using MBE technique — •R. Hassdorf¹, J. Feydt², and M. Moske¹ — ¹Thin adaptive films, Research center caesar, 53175 Bonn, Germany — ²Electron microscopy, Research center caesar

In a theoretical approach using ab initio calculations, we established that in the system Ni-Mn-Al the magnetic ground state close to the Heusler stoichiometry is ferromagnetic ordered [1]. Moreover, as for the lattice dynamics of the system, the cubic L2₁ Heusler structure is shown to be unstable against shear displacement along the [110] direction which confirms the tendency to form modulated martensitic structures in this regime. Indeed, such structures, namely 2M and 14M, are found experimentally in coexistence within thin film samples grown by MBE technique, with a composition around Ni₅₀Mn₃₀Al₂₀.

The structural transition from the disordered B2 to the fully ordered L2₁ phase is subject of current investigations. Hereto, NiMn(Ga,Al) alloy thin films were realized by co-deposition of Ni, Mn, and Al on top of single-crystal GaAs at elevated temperatures. As demonstrated from XPS and Auger depth profiling, Ga is incorporated into the film structure almost homogeneously due to its high diffusion mobility. An epitaxial relationship between film and substrate has been confirmed by RHEED. The compositional and microstructural aspects will be discussed.

[1] T. Büsgen, J. Feydt, R. Hassdorf, S. Thienhaus, M. Boese, A. Zayak, P. Entel, and M. Moske, Phys. Rev. B 70, 014111 (2004).