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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.
2
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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.
3
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Anisotropy of the Magnetocaloric Effect in the Ni_{49.6}Mn_{27.6}Ga_{22.8} Single Crystal

100%
Wroblewski R., Sielicki K., Leonowicz M.
Acta Physica Polonica A
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2015
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vol. 128
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issue 1
54-55
EN
The magnetocaloric effect anisotropy in the Ni_{49.6}Mn_{27.6}Ga_{22.8} single crystal was investigated. In the examined alloy the structural phase transition and magnetic transition occur at room temperature and around 370 K, respectively. The magnetic entropy change, at those two temperatures, was determined on the basis of isothermal and isofield curves, recorded at fields up to 1200 kA/m (1.5 T) with temperature steps of 2.5 and 5 K. Although the calculated values of magnetic entropy change are relatively small, ≈0.7 J/(kg K), an anisotropy of the magnetocaloric effect is observed with a magnetic field applied along the main crystallographic directions of the single crystal. The magnetic entropy change at the structural phase transition depends on the orientation. The weakest magnetocaloric effect occurs when the field is applied along [1 0 0] direction whereas the highest magnetocaloric effect value is reached along [0 0 1] direction, which is an easy magnetization axis. Such behaviour can be explained with the high magnetocrystalline anisotropy of the martensitic phase. The magnetic entropy change value, at the structural phase transition, obtained for the polycrystalline specimen, is close to that for the [0 0 1] single crystal direction.
4
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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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5
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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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