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A Comparative Studies of Magnetocaloric Effect in Ni-Mn-Cu-Ga and Ni-Mn-Pb-Ga Alloys

100%
Sielicki K., Wróblewski R., Leonowicz M.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
644-646
EN
Effect of Pb substitution for Cu on magnetocaloric properties of Ni₂Mn_{1-x}Cu_xGa (x = 0.25, 0.27, 0.29) alloy was investigated experimentally. The magnetic measurements of Ni-Mn-Pb-Ga alloys conducted at low field of 4kA/m (50 Oe) showed that their Curie points are above the room temperature (RT). The analysis of isothermal magnetic curves allowed the estimation of magnetic entropy change (ΔS_{M}). The highest calculated value of |ΔS_{M}|, ≈ 12 J/(kgK) and ≈ 1.8 J/(kgK), was registered for alloys containing 6.25 at.% of Cu and 6.75 at.% of Pb, respectively. The adiabatic temperature changes (ΔT) measured near RT are ≈ 0.4 K.
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Magnetocaloric Effect in Ni-Cu-Mn-Gd-Ga Alloy. XI Symposium of Magnetic Measurements

100%
Sielicki K., Wróblewski R., Leonowicz M.
Acta Physica Polonica A
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2015
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vol. 128
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issue 1
120-122
EN
The magnetocaloric effect of the Ni-Cu-Mn-Gd-Ga polycrystalline alloy was investigated. The nominal composition of the alloy was Ni_{50}Cu_{6.25}Mn_{16.75}Ga_{25}Gd_{2} at.%. The X-ray diffraction studies revealed presence of two phases at room temperature. This was confirmed by magnetic measurements conducted in low field of 4 kA/m (50 Oe), which showed two Curie transition temperatures, one in vicinity and the other one well above the room temperature. The analysis of isothermal magnetic curves allowed the calculation of magnetic entropy change (ΔS_{M}). Although the peak value of |ΔS_{M}| is relatively low, ≈1.1 J/(kg K), it is very broad. The adiabatic temperature change (ΔT) measured near room temperature is ≈0.49 K. Such result is irrespective of the magnetizing-demagnetizing cycle frequency which varied from 2/min to 10/min.
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The Magnetic Entropy Changes in Pb Doped Ni-Mn-Cu-Ga Alloys

89%
Sielicki K., Zygmuntowicz J., Wróblewski R., Leonowicz M., Sielicki K., Zygmuntowicz J., Wróblewski R., Leonowicz M.
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4
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Entropy Change Calculations for Pure Gd and a Ni-Mn-Cu-Ga Heusler Alloy: Constant Field vs. Constant Temperature Experiment

76%
Ferenc J., Kowalczyk M., Wróblewski R., Cieślak G., Sielicki K., Leonowicz M., Kulik T.
Acta Physica Polonica A
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2015
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vol. 128
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issue 1
111-115
EN
The magnetocaloric effect may be assessed indirectly by expressing it as the change in magnetic entropy in varying magnetic field, H, as the function of temperature, T. Magnetization, M=f(T,H), may be experimentally acquired from a series of isothermal measurements with variable field, or from a series of constant field measurements with variable temperature. The accuracy of magnetic entropy calculation depends on the number of series in these experiments. The aim of this work is to determine how little data is sufficient to obtain accurate results of magnetic entropy change calculations, on the basis of real, magnetocaloric materials. Pure gadolinium and a Ni-Mn-Cu-Ga Heusler alloy were studied. For both materials, the magnetic entropy change and relative cooling power were calculated from both experiments, with the decreasing number of experimental data. For both materials, the constant field experiment with only 6 field values provided only a 5% error of calculations, as compared to the experiment with 100 field values. The Arrott plots were also drawn for constant field mode with 6 field values, easily indicating the order of transition. Comparison of the calculation results suggests that the constant field mode magnetization measurement may be more accurate and faster than isothermal mode.
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