Acoustical properties of Ni-Mn-Ga ferromagnetic shape memory alloys (FSMA) have been studied intensively in the recent years in connection with the martensitic and magnetic transitions phenomena which take place in these substances. Recently the effects of intense ultrasound upon the martensitic transitions in NiMnFeGa polycrystals [1] on the giant magnetic-field-induced strains due to martensitic domains boundaries movement in NiMnGa single crystals [2] have been observed. These effects may be of interest in view of possible applications of single and polycrystalline FSMA in sensor and actuator technology.

The aim of the present work is to study experimentally and theoretically the ultrasound velocity anomalies and acoustical emission accompanying the martensitic transition in polycrystalline Ni_2.14Mn_0.81Fe_0.05Ga FSMA. Another purpose of the work is to investigate the effects of intense pulsed ultrasound on the martensitic transition and pseudoplastic deformation of the FSMA samples. The low field magnetic susceptibility and sample strain versus temperature curves were plotted depending on the regime of ultrasound pulses. The effect of ultrasound is found to narrow the hysteretic loop of martensitic transition. The partial martensitic transition accompanied by pseudoplastic sample strain due to ultrasound at constant temperature is observed. The optical in situ observations of martensitic domains structure evolution due to ultrasound action were performed.

This work is supported by RFBR (Grants 03-02-17443, 04-02-81058, 03-02-39006).

[1] V.Buchelnikov, I.Dikshtein, R.M.Grechishkin, et.al, JMMM, 272-276 (2004) 2025.

[2] B.W.Peterson, J.Feuchtwanger, J.M.Chambers, et.al. J. Appl. Phys. 95 (2004) 6963.

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