In this work, we report on the observation of two coexisting patterns in Magnetic Force Microscopy (MFM) images of shape memory alloys. The MFM signal of both patterns presents similar behavior with tip-surface separation. An investigation on the origin of these patterns presents strong evidence that both are of magnetic nature only and, furthermore, can be assigned as bulk and surface-related, respectively.

Shape memory alloys are a class of materials that exhibit martensitic transformation [1]. The shape memory effect, which may be defined as the property of recovering its original shape during a thermal cycle after a material has been apparently deformed in a permanent way, is found in several materials, including the Fe-Mn-Cr-Ni-Si alloy, studied in this work [1]. A standard metalographic process was employed to reveal ferritic-phase islands surrounded by the austenitic-phase matrix, which constitute the structure of this alloy. The images were acquired with a MultiMode microscope from Digital Instruments.