The investigation of longitudinal acoustic waves in Heusler Ni53Mn25Ga22 alloy crystal with coupled magnetostructural transition
|Yuri A. Kuzavko|
The Polesie Agrarian Ecological Institute of the National Academy of Science of Belarus (PAEI), Brest 224000, Belarus
|Heusler Ni53Mn25Ga22 ferromagnetic alloy crystal (sizes 4.0 x 3.8 x 10 mm) with shape memory effects (SME) has the coupled magnetostructural phase transition (the austenite starting temperature As=116oC and finishing one At=134oC, the martensite starting temperature Ms=109oC and finishing one Mt=97oC) below the Curie temperature Tc=134o C. This characterising temperatures were defined by acoustical measurements using the longitude uldtrasound transducers with 2.8, 3.5, 5 MHz resonance frequences. Temperature was measured with accuracy of 0.025K, the minimal heating speed was 1 K / 3 min and holding one was 1 K / 10 min. The sample is placed at 2 Oe constant magnet at necessity. Sample was temperature-controlledm heated with a low-ohm warmer from a power supply. Temperature was measured by termo-couple and microvolmeter.
This alloy has reversible thermoelastic martensite transitions. The process of a return to parent shape is coupled with a reveversible transition of a deformed martensite (D4h) phase into a high-temperature austenitic (Oh) one. For our crystall the lattice parameters are a=b=0.7753 nm, c=0.6598 nm, as for Ni2MnGa a=b=0.5920 nm, c=0.5566 nm at D4h phase, a=0.5825 nm at Oh.
We have studied experimentally the temperature dependences of the ultrasound speed and amplitude of pulse signals my means of digital measuring equipments.
The presence of a soft transverse mode TA2 takes place for the alloy . It propagates along directions  and related with accession to zero of the elasticity constant c`=(c11-c12)/2. The theory was designed for investigated effects consisting the linear and nonlinear magnetoacoustical ones.
Presentation: Oral at E-MRS Fall Meeting 2008, Symposium C, by Yuri A. Kuzavko
See On-line Journal of E-MRS Fall Meeting 2008
Submitted: 2008-05-30 10:29 Revised: 2009-06-07 00:48