In Ni-Mn-Ga alloys coupled magnetostructural transition (MST) may occur. The giant magnetocaloric effect (MCE) observed during MST in Ni-Mn-Ga alloys is regarded promising for the development of economical and ecological refrigerants working near room temperature. In this work we study MCE during MST by two experimental methods. A direct MCE measurement is performed with the Ni_2.19Mn_0.81Ga sample immersed into the calorimetric system. The largest entropy change at change of magnetic field from 0 to 26 kOe are equal about 9 J/kgK if temperature is increased and about 11 J/kgK if temperature is decreased. In the second method we are used the indirect measurements using the magnetization temperature dependences. From these dependences MCE values are deduced with the help of Maxwell relation. Most attention is concentrated on MCE behavior in the region of MST hysteresis. This is important, because, firstly, MCE has sharp peaks at the edges of MST hysteresis, and, secondly, it is the region for which the traditional indirect method of MCE measurement is least effective, because the thermodynamical relations are justified only for reversible 2nd order transitions. The experimental data are compared with each other and with the theoretical results which were obtained by the help of phenomenological theory based on the statistical physics and the molecular field theory. This work was supported RFBR (grants 03-02-17443, 04-02-81058, 03-02-39006).

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