Berlin 2012 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 45: Joint Session "Magnetic Shape Memory Alloys II" (jointly with DS, MM)
MA 45.12: Vortrag
Donnerstag, 29. März 2012, 18:00–18:15, H 0112
Mapping local elasticity of twinned martensitic NiMnGa films using atomic force acoustic microscopy — •Yuansu Luo1, Walter Arnold1,2, and Konrad Samwer1 — 1I.Physikalisches Institut, Universität Göttingen — 2Fachbereich Werkstoffwissenschaften der Universität des Saarlandes, Saarbrücken
Local elasticity of magnetic shape memory films NiMnGa was mapped qualitatively and quantitatively on nanometer scale by means of atomic force acoustic microscopy (AFAM). The films (100nm) used were prepared on MgO substrates by magnetron sputtering. The first bending resonance vibrations of the AFM cantilever were measured by sweeping the frequency from 0.5 to 3MHz. Different contact stiffness was measured in this way for martenstic twin variants due to their anisotropic crystallography. Broad and multi-resonance behavior was observed, reflecting the damping and multi-variant properties of 7-layer modulated martensite. The stiffness image mapped by the measured resonance frequency exhibits however a contrast opposite to the height image mapped by conventional AFM. The result can be associated with the mobility of twin boundaries, namely they are mobile at the top and immobile at bottom of twin lamellas. The load dependent contact indentation was measured. A softening emerges at a critic force and can be contributed to moving of twin boundaries under the local mechanical load. The local elastic moduli were calibrated by a standard sample (SrTiO3). The values evaluated are in the range from 170 to 230 GPa, enlarged by a factor of about 10 compared to stress-free bulk samples. (Supported by BMBF-13N10061)