Thermal, acoustic and magnetic noises emitted during martensitic transformation in single crystalline Ni45Co5Mn36.6In13.4 meta-magnetic shape memory alloy
- Additional Document Info
- View All
© 2018 Elsevier B.V. Meta-magnetic shape memory alloys (MMSMAs) display an abrupt change in magnetization across the martensitic transformation. Simultaneous detection and statistical analysis of the emitted acoustic and magnetic noises, accompanied with martensitic transformations are important for better understanding of the magneto-structural coupling, and for utilization of well-characterized acoustic and magnetic signals for practical applications. In the present work, characteristics of thermal, acoustic and magnetic noises, detected during martensitic transformation in the Ni45Co5Mn36.6In13.4 MMSMA single crystals, were investigated for the first time. Statistical analysis of the thermal spikes, appeared during the calorimetric measurements at low cooling rates (typically below 1 K/min) showed that the energy distributions followed a power law with ε = 2.0 ± 0.3 exponent, which is in good agreement with the exponents of energy distribution of acoustic and magnetic emission events (ε = 1.7 ± 0.1 and ε = 1.7 ± 0.2, respectively). The above exponents were independent of the external magnetic field between B = 0 and 230 mT. Interestingly, the acoustic and magnetic exponents during cooling and heating were the same in contrast to the expected asymmetry based on the fact that the transformation demonstrates an isothermal character during cooling and an athermal one for heating. Upon interrupting cooling, and dwelling at a temperature above the martensite finish temperature, practically no acoustic and magnetic noises were detected, while upon continued cooling the noise appeared again, with the same critical exponents. This indicates that the main discontinuous events, leading to noise emissions, should be the same before and after dwelling as well as during cooling and heating. In magnetic noise measurements, under zero external field, the magnetic noise packets contained voltage peaks in the detector coils in both (positive and negative) directions. Under small external magnetic fields (between 20 and 230 mT), the activity of magnetic signals increased and the magnetic peaks, during both heating and cooling, appeared more and more unidirectional (i.e. peaks only in one direction were observed) which can be attributed to the increased magnetization of the austenite.
author list (cited authors)
Samy, N. M., Bolgár, M. K., Barta, N., Daróczi, L., Tóth, L. Z., Chumlyakov, Y. I., Karaman, I., & Beke, D. L.