Nanoscale mechanical surface properties of single crystalline martensitic Ni-Mn-Ga ferromagnetic shape memory alloys

Located beyond the resolution limit of nanoindentation, contact resonance atomic force microscopy (CR-AFM) is employed for nano-mechanical surface characterization of single crystalline 14M modulated martensitic Ni-Mn-Ga (NMG) thin films grown by magnetron sputter deposition on (001) MgO substrates. Comparing experimental indentation moduli-obtained with CR-AFM-with theoretical predictions based on density functional theory (DFT) indicates the central role of pseudo plasticity and inter-martensitic phase transitions. Spatially highly resolved mechanical imaging enables the visualization of twin boundaries and allows for the assessment of their impact on mechanical behavior at the nanoscale. The CR-AFM technique is also briefly reviewed. Its advantages and drawbacks are carefully addressed.