Tracking Twin Boundary Jerky Motion at Nanometer and Microsecond Scales

• Published in: Advanced functional materials Vol. 31; no. 50
• Main Authors: Bronstein, Emil, Tóth, László Zoltán, Daróczi, Lajos, Beke, Dezsö László, Talmon, Ronen, Shilo, Doron
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.12.2021
• Subjects: Avalanches; Barkhausen noise; Exponential functions; Ferromagnetism; Martensitic transformations; materials mechanics; Materials science; Mathematical analysis; Physical properties; Shape memory alloys; Statistical distributions; Twin boundaries; twin boundary
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202106573

The jerky motion of twin boundaries in the ferromagnetic shape memory alloy Ni‐Mn‐Ga is studied by simultaneous measurements of stress and magnetic emissions (ME). A careful design of the experimental conditions results in an approximately linear relationship between the measured ME voltage and the nm‐scale volumes exhibiting twinning transformation during microsecond‐scale abrupt “avalanche” events. This study shows that the same distributions of ME avalanches, related to features of jerky twin boundary motion, are found both during and between stress drop events. Maximum likelihood analysis of statistical distributions of several variables reveals a good fit to power laws truncated by exponential functions. Interestingly, the characteristic cutoffs described by the exponential functions are in the middle of the distribution range. Further, the cutoff values can be related to the physical characteristics of the studied problem. Particularly, the cutoff of amplitudes of ME avalanches matches the value predicted by high rate magnetic pulse tests performed under much larger driving force values. This observation implies that avalanches during slow rate twin boundary motion and velocity changes observed by high rate tests represent the same behavior and can be described by the same theory. A developed magnetic‐emission‐based experimental procedure enables measuring nanometer scale volumes that undergo a twinning transformation during a multitude of discrete and impulsive events, which occur at the microsecond scale. Based on the obtained experimental results, a unified description of the nature of twin boundary motion at both slow and high rates is proposed.