Some metal alloys have reversible thermoelastic martensite transitions with shape memory effects (SME). SME coupled with a reversible transitions from a deformed martensite phaseinto the high-temperature austenitic ones. Ferromagnetic crystal of Ni₅₃Mn₂₅Ga₂₂ Heysler alloy (austenite starting temperature A_s=116⁰C and finishing one A_f=134⁰C, martensite starting temperature M_s=109⁰C and finishing one M_f=97⁰C, Curie temperature T_c=134⁰C) with a coupled magnetostructural transithions [1]allowes to get the decrease of a magnetic field magnitude, to controll the reversible change of the sample dimensions (4x4x10 mm sample in our case). For our crystal of Ni₅₃Mn₂₅Ga₂₂ the lattice parameters a=b=0.7753 nm, c=0.6598 nm, as for Ni₂MnGa a=b=0.5920 nm, c=0.5566 nm at D_4hphase, a=0.5825 nm at O_h. The investigations of SME are aimed to combine rapid response with large reversible deformations. The decrease of a magnetic field magnitude for a controlled SME is a common problem for a wide engineering applications of such materials.

The presence of a soft acoustical transverse mode TA₂with k=(¹/₃, ¹/₃, 0) wave vector and [110] polarization takes place for Heysler alloys. It is related with accession to zero of the elastic constant c'=(c₁₁-c₁₂)/2 [2].

The sample was temperature-controlled in experiment. The accuracy of measuring was 0.025 К, the minimal speed of heating - 1 К / 3 min., the sample was placed in constant magnet of 2 kOe at necessity. All five characterizing temperatures of crystal were definable from acoustical measuring.

Authors are grateful for BRFFI and RFFI (F04R-080, 04-02-81058 grants) and ME RB (grant 05-505) for their financial support of carried out researches.

1. C. Jiang, G. Feng, H. Xu. Appl. Phys. Lett. 2002. V.80. pp. 1619-1621.

2. T.E. Stenger, J. Trivisonno. Phyics. Rev.B 1998. V. 57. pp. 2735-2739.

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