In-situ study of surface relief due to cubic-tetragonal martensitic transformation in Mn69.4Fe26.0Cu4.6 antiferromagnetic shape memory alloy

Temperature-dependence surface relief during cubic↔tetragonal martensitic transformation (MT) in Mn69.4Fe26.0Cu4.6 antiferromegnetic shape memory alloy was studied by means of in-situ atomic force microscopy. The surface morphology memory effect was found and the crystallography reversibility of the transformation and its shearing characters were directly verified. Twin shearing is suggested as the main mechanism of formation of tent-type surface relief. The surface relief angle (θα|θβ)<0.5° was firstly measured and might be the smallest compared with that in other shape memory alloys. A Landau model was proposed to consider the shearing strain related with surface relief of MT varying with the coupling effect between second-order antiferromagnetic transition and first-order MT. According to this model, the Mn69.4Fe26.0Cu4.6 alloy belongs to the weak coupling system and this kind of weak coupling effect makes the main contribution to the small relief angle.