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  1. 74 Acta Physica Polonica A

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  1. 11 Gębara P.

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1
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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
|
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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Magnetocaloric Effect of the Tb_{1-x}Y_{x}NiAl and TbNiAl_{1-y}In_{y} Series

100%
Kaštil J., Javorský P., Klicpera M.
Acta Physica Polonica A
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2010
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vol. 118
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issue 5
888-890
EN
We have studied the development of the magnetocaloric effect in the (Tb,Y)NiAl and TbNi(Al,In) series as determined from magnetization measurements. The transition from antiferromagnetic order in TbNiAl to ferromagnetic order in Tb_{0.7}Y_{0.3}NiAl is accompanied by increase of the maximum entropy change from - 4.1 to - 4.4 J kg^{-1} K^{-1}. In the TbNi(Al,In) series, the change of uniaxial anisotropy in TbNiAl to the easy-plane anisotropy in TbNiIn leads to broadening of the magnetocaloric effect accompanied with large increase of the relative cooling power from 66 to 120 J kg^{-1}.
4
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Magnetocaloric Cooling Device with Reciprocating Motion of the Magnetic Field Source

63%
Kolano R., Kolano-Burian A., Hreczka M., Polak M., Szynowski J., Tomaka W.
Acta Physica Polonica A
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2016
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vol. 129
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issue 6
1205-1209
EN
This paper describes the magnetic cooling device model designed and built at the Institute of Non-Ferrous Metals in Gliwice, which utilizes reciprocating motion of a magnetic field source and a cyclic flow of a coolant through regenerator. The regenerator made from gadolinum made it possible to obtain an adiabatic temperature change of 2.5 K at the magnetic field of 0.8 T. The magnetic field source was built using neodymium magnets according to our own technology. For the heat transfer, a liquid having the specific heat of about 4000 J/(kg K) has been applied. We have also developed and applied a special driving system enabling reciprocating motion of the magnetic field source and of the pistons in the hot and cold heat exchangers. The tests were made with this cooling model showing that it was possible to obtain, at the frequency of 0.5 Hz, the liquid temperature gradient of 4 K. The potential energy savings resulting from application of this device have been evaluated and compared with the literature data presenting a pre-industrial prototype of the magnetic refrigerator utilizing similar solutions to those applied in our cooling model.
5
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Effect of Si Substitution and Annealing on Magnetocaloric Properties in TbCo_2

63%
Janatova M., Poltierova Vejpravova J., Javorsky P., Prokleska J., Svoboda P., Danis S.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
311-314
EN
We report on magnetocaloric properties of the as-cast and annealed TbCo_2 with partial substitution of cobalt by silicon. The samples were characterized by powder X-ray diffraction and investigated by heat capacity measurements (8-300 K, in fields 0 T and 1 T). TbCo_2 undergoes a second-order type phase transition at T_C = 240 K, from paramagnetic to ferrimagnetic state;similar behavior was revealed in the Si-doped compounds. The temperature dependence of magnetic entropy and the corresponding magnetocaloric effect were derived for all studied samples. The influence of the heat treatment and Si doping on magnetocaloric properties will be discussed in context of the analogue case Er(Co_{1-x}Si_x)_2.
6
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Magnetic Phase Transitions and Thermal Properties of Ho(Co_{1-x}Si_x)_2 Compounds

63%
Vasylyev D., Prokleška J., Sechovský V.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
347-350
EN
The specific heat of HoCo_2 and Ho(Co_{0.95}Si_{0.05})_2 was measured as a function of temperature in several constant magnetic fields up to 8 T. A data analysis allowed us to determine the isothermal entropy change and the magnetocaloric effect in a wide temperature range. The considerable values of the magnetocaloric effect in the vicinity of the magnetic ordering transition are qualifying both compounds as suitable for magnetic refrigeration purposes. The magnetic phase transition temperature (T_C) increases from 77 K for HoCo_2 to 103 K for Ho(Co_{0.95}Si_{0.05})_2 while the large magnetocaloric effect in the vicinity of TC is maintained, which demonstrates possible ways of tuning the operating temperatures of the magnetic refrigerant.
7
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Experimental Study of the Magnetocaloric Effect in the Two-Dimensional Quantum System Cu(tn)Cl_2

63%
Baranová L., Tarasenko R., Orendáčová A., Orendáč M., Pavlík V., Feher A.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
256-257
EN
Magnetocaloric studies of a two-dimensional antiferromagnet Cu(tn)Cl_{2} (tn=1,3-diaminopropane=C_3H_{10}N_2) have been performed by adiabatic magnetization and demagnetization measurements, in the temperature range from 0.2 to 4 K and magnetic fields up to 2 T. The compound represents an S=1/2 spatially anisotropic triangular-lattice antiferromagnet. The magnetocaloric measurements were focused at the identification of the phase transition to the magnetically ordered state which was not indicated in the previous specific heat studies. Furthermore, the interplay of the magnetic-field induced easy-plane anisotropy and the intrinsic spin anisotropy present in the studied system should manifest in low magnetic fields. The obtained results of the magnetocaloric experiments of Cu(tn)Cl_{2} indicate a double crossover from the normal to inverse magnetocaloric effect (MCE). The first crossover from the normal to inverse MCE occurring at about 0.3 K can be attributed to the competition of the aforementioned anisotropies. The second crossover from the inverse to normal MCE observed at about 2.2 K might be ascribed to the formation of spin vortices stabilized by the easy-plane anisotropy introduced by magnetic field.
8
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Influence of Partial Substitution of Fe by Mn on the Thermomagnetic Properties of Magnetocaloric LaFe_{11.2}Co_{0.7}Si_{1.1} Alloy

63%
Gębara P., Marcin J.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
648-650
EN
The aim of this paper was to study the influence of partial substitution of Fe by Mn in the LaFe_{11.2-x}Mn_{x}Co_{0.7}Si_{1.1} (where x=0.1, 0.2 and 0.3) alloys. Measurements revealed that a systematic increase of Mn in the alloy composition resulted in a decrease of the Curie temperature, which correlated with a decrease of the lattice parameter of the La(Fe,Si)₁₃- type phase. For samples corresponding to Mn content x=0.1 and 0.2 a decrease of magnetic entropy change was observed. However in the case of the sample with x=0.3 an increase of magnetic entropy change was detected.
9
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Measurements of Magnetocaloric Effect in LaFe_{11.14}Co_{0.66}Si_{1.2-x}Al_{x} (x=0.1, 0.2, 0.3) Alloys

63%
Gębara P., Pawlik P., Michalski B., Wysłocki J.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
576-578
EN
In the present work, phase constitution and thermomagnetic properties of LaFe_{11.14}Co_{0.66}Si_{1.2-x}Al_{x} (where x = 0.1, 0.2, 0.3) alloys were investigated. Ingot samples were obtained by arc-melting under the low pressure of Ar atmosphere. Subsequently samples were annealed at 1323 K for 15 days. X-ray diffraction of all samples revealed coexistence of two crystalline phases dominant La(Fe,Si)_{13}-type and minor bcc α -Fe. Furthermore, the magnetic measurements at various temperatures allowed to study the Curie temperature, magnetic entropy changes and relative cooling power.
10
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Investigation of Critical Behavior in Gd₇₅Ge₁₅Si₅Ce₅ Alloy

63%
Gębara P., Hasiak M.
Acta Physica Polonica A
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2017
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vol. 131
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issue 5
1232-1235
EN
The main goal of the present work was to study the critical behavior in the as-quenched Gd₇₅Ge₁₅Si₅Ce₅ (wt%) in the vicinity of the critical temperature T_{C}. The second order phase transition from a ferro- to a paramagnetic state was confirmed by the positive slope of the Arrott plots and analysis of temperature evolution of the Landau coefficients. The critical exponents have been revealed using the Kouvel-Fisher method and yield β=0.376±0.006, γ=1.032±0.006 and δ=3.835±0.008. The Curie temperature for the as-quenched Gd₇₅Ge₁₅Si₅Ce₅ equals 275.7±0.1 K.
11
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Magnetocaloric Effect in Geometrically Frustrated Magnetic Compound HoB_{12}

63%
Snyman J., Flachbart K., Gabani S., Reiffers M., Shitsevalova N., Siemensmeyer K., Strydom A.
Acta Physica Polonica A
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2010
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vol. 118
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issue 5
873-874
EN
The magnetocaloric effect of frustrated antiferromagnetic HoB_{12} is calculated. The isothermal entropy change Δ S characterising the magnetocaloric effect shows a small positive change upon magnetisation below the transition temperature T_{N}, indicating a small inverse magnetocaloric effect. At T_{N}, Δ S shows clear scaling behaviour with the applied magnetic field. The adiabatic temperature change Δ T shows paramagnetic behaviour above T_{N}, despite strong magnetic correlations that persist in this temperature region. The adiabatic temperature change calculated for HoB_{12} is appreciable.
12
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Investigations of the Magnetic Phase Transition in the LaFe_{11.14}Co_{0.66}Si_{1.1}M_{0.1} (Where M = Al or Ga) Alloys

63%
Gębara P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
798-800
EN
The aim of the present work was to study the phase transition in the LaFe_{11.14}Co_{0.66}Si_{1.1}M_{0.1} (where M = Al or Ga) alloys. Research was carried out using field dependences of magnetization measured at a wide temperature range. Positive slope of the Arrott plots showed that magnetic phase transition in both investigated samples was of second order nature. The temperature dependences of the Landau coefficients also revealed second order phase transition in both specimens. The analysis carried out using universal curve confirmed second nature of phase transition in both samples.
13
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Investigations of the Magnetization Reversal Processes in Nanocrystalline Nd-Fe-B Alloys Doped by Nb

63%
Kaźmierczak M., Pawlik P., Wysłocki J., Wnuk I., Gębara P., Pawlik K., Przybył A.
Acta Physica Polonica A
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2017
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vol. 131
|
issue 4
789-791
EN
In the following article the magnetic properties and phase composition of (Nd₁₀Fe₆₇B₂₃)_{100-x}Nb_{x} (where x=5, 6, 7, 8, 9) alloys in the form of ribbons are discussed. The X-ray diffraction studies revealed the coexistence of amorphous and nanocrystalline structures consisting of Nd₂Fe₁₄B, Nd_{1+ε}Fe₄B₄ and metastable Nd₂Fe₂₃B₃ phases. The shape of M_{rev} (M_{irr}) suggests that the magnetization reversal proceeds through the nucleation of the reversal domain for the ribbon doped with 5-7 at.% of Nb and the subsequent pinning of the domain walls for ribbons doped with 8 and 9 at.% of Nb.
14
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About the Role of Fe-Ions in the Formation of Magnetocaloric Effect in Ho(Co_{1-x}Feₓ)₂ Compounds

63%
Anikin M., Tarasov E., Kudrevatykh N., Osadchenko V., Zinin A.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
635-637
EN
A study of crystalline structure, magnetic and magnetocaloric properties of Ho(Co_{1-x}Feₓ)₂ (x = 0.09, 0.12) intermetallic compounds has been undertaken. Phase composition was controlled by X-ray diffraction analysis. Magnetic properties were measured within the temperature range 4.2-350 K in magnetic fields up to 7 T. Magnetic ordering temperatures corresponding to paramagnetic-ferrimagnetic phase transitions were found to be 199 K and 258 K respectively. Temperature dependences of heat capacity for these compounds have been inferred for the temperature interval 77-340 K. Comparison of magnetocaloric effect (MCE) values determined by direct measurement and by calculation was carried out as well. It was found that significant MCE peak broadening occurs for higher iron concentration in the compound.
15
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The Remark about an Analogy between Magnetocaloric Behaviour of Type II Superconductors and Ferromagnetic Materials

63%
Kalva Z., Mánek P.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
407-410
EN
The analogy between magnetocaloric behaviour of type II superconductors and anisotropic ferromagnetic materials is discussed. Special attention is devoted to the influence of anisotropy on the negative magnetocaloric effect near phase transitions.
16
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Effect of Ga Addition on Structure and Magnetic Properties of the LaFe_{11.14}Co_{0.66}Si_{1.2-x}Ga_{x} (x=0.1, 0.2, 0.3) Alloys

63%
Gębara P., Pawlik P., Michalski B., Wysłocki J., Kotynia K.
Acta Physica Polonica A
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2015
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vol. 128
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issue 1
87-90
EN
In the present work, the phase constitution and magnetic properties of the LaFe_{11.14}Co_{0.66}Si_{1.2-x}Ga_{x} (where x=0.1, 0.2, 0.3) alloys, were investigated. It was revealed that increase of Ga content in the alloy composition causes the rise of lattice parameter of the La(Fe,Si)_{13}-type phase, which causes increase of the Curie temperature. However, the increase of Ga addition leads to decrease of magnetocaloric effect.
17
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Thermomagnetic Properties of LaFe_{11.0}Co_{0.8}(Si_{1-x}Al_{x})_{1.2} (x=0, 0.6) Alloys

63%
Gębara P., Pawlik P., Skorvanek I., Marcin J., Pawlik K., Przybył A., Wysłocki J., Szwaja M., Filipecka K.
Acta Physica Polonica A
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2014
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vol. 126
|
issue 1
166-167
EN
In the present work, Curie temperature, refrigeration capacity and cooling power of the LaFe_{11.0}Co_{0.8}(Si_{1-x}Al_{x})_{1.2} (where x=0, 0.6) alloys, are investigated. The value of Curie temperature was found to be 280 and 290 K for x=0 and 0.6, respectively. The determined values of cooling power (RCP) and refrigeration capacity (RC) differ only slightly for both investigated alloys. The maximum values of RCP and RC obtained under the change of external magnetic field from 0 to 5 T are 433 J/kg (for x=0) and 290 J/kg (for x=0.6), respectively.
18
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Entropy Change Calculations for Pure Gd and a Ni-Mn-Cu-Ga Heusler Alloy: Constant Field vs. Constant Temperature Experiment

63%
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.
19
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Influence of Fe Addition on the Martensitic Transformation, Structure and Magnetic Properties of Metamagnetic Ni-Co-Mn-Sn Alloys

63%
Wójcik A., Maziarz W., Szczerba M., Sikora M., Hawełek Ł., Czaja P.
Acta Physica Polonica A
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2016
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vol. 130
|
issue 4
1026-1028
EN
In this study the effect of Fe for Ni substitution in Ni₄₄Co₆Mn₃₉Sn₁₁ metamagnetic shape memory alloys on their structure, magneto-structural transformation characteristics, magnetic and magnetocaloric properties was studied. The results show that the structure and martensite transformation behavior strongly depends on the Fe concentration. The martensitic transformation temperature decreases with 1 at.% of Fe and is suppressed with higher Fe content. It was further found that substitution of Fe for Ni leads to lowering of the value of magnetic entropy change.
20
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Magnetocaloric Study of S=1/2 Low-Dimensional Heisenberg Antiferromagnet [Cu(phen)(H_2O)_2]SO_4

63%
Sedláková L., Orendáč M., Kajňaková M., Orendáčová A., Feher A.
Acta Physica Polonica A
|
2008
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vol. 113
|
issue 1
473-476
EN
We present the experimental study of magnetocaloric effect on powder sample [Cu(phen)(H_2O)_2]SO_4 (phen = phenantroline = C_{12}H_8N_2) in the temperature range from nominally 0.2 K to 4 K and in magnetic fields up to 2 T. The values of total entropy were extracted from the experimental data obtained by adiabatic demagnetization. The comparison was performed with the temperature dependence of the entropy for S=1/2 paramagnet calculated at selected magnetic fields. The deviations observed below 0.6 T were attributed to internal field mediated by exchange coupling. In addition, the temperature response observed in [Cu(phen)(H_2O)_2]SO_4 revealed very short relaxation time below 1 K. The comparison of the behavior observed at the end of the demagnetization in [Cu(phen)(H_2O)_2]SO_4 and other systems suggests that the magnetocaloric effect can serve as an alternative tool for studying slow magnetic relaxation.
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