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1

Nanocrystalline Permanent Magnets with Enhanced Properties

100%

Leonowicz M.

Acta Physica Polonica A

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2002

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vol. 102

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issue 1

35-43

EN

Parameters of permanent magnets result from the combination of intrinsic properties such as saturation magnetization, magnetic exchange, and magnetocrystalline energy, as well as microstructural parameters such as phase structure, grain size, and orientation. Reduction of the grain size into nanocrystalline regime (≈50 nm) leads to the enhanced remanence which derives from ferromagnetic exchange coupling between highly refined grains. In this study the fundamental phenomena, quantities, and structure parameters, which define nanophase permanent magnets are presented and discussed. The theoretical considerations are confronted with experimental data for nanocrystalline Sm-Fe-N type permanent magnets.

2

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

51%

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.

3

Magnetocaloric Effect in Ni-Cu-Mn-Gd-Ga Alloy. XI Symposium of Magnetic Measurements

51%

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.

4

Structure and Properties of Nd-Fe-B Alloy Subjected to HDDR Process

51%

Szymański M., Michalski B., Leonowicz M., Miazga Z.

Archives of Metallurgy and Materials

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2016

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issue 1

5

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

51%

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.

6

Structural and Thermophysical Properties of Magnetic Beads Containing Metallic Nanocrystallites

51%

Izydorzak M., Leonowicz M., Skumiel A.

Acta Physica Polonica A

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2012

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vol. 121

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issue 1

68-70

EN

Cobalt, iron, nickel and iron carbide nanocrystallites, stabilized within carbon beads, were prepared by the three-step procedure including formation of metal acrylamide complex, followed by frontal polymerization and pyrolysis of the polymer at various temperatures. The beads containing the nanocrystallites exhibit domination of the ferromagnetic ordering. The analysis of calorimetric results allowed estimation of the efficiency of the hyperthermal effect, under the influence of an alternating magnetic field. The XTT tests show that the extracts prepared on the basis of the Fe_3C containing beads are nontoxic, whereas these made of the composites containing Co and Ni exhibit negligible cytotoxicity for the test article/vehicle ratios 6.25 and 3.125 mg/ml.

7

Consolidation of Nanocrystalline Nd-Fe-B Powder by Hydrostatic Extrusion at High Temperature

51%

Gizynski T., Kaszuwara W., Kulczyk M., Leonowicz M.

Acta Physica Polonica A

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2017

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vol. 131

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issue 5

1260-1263

EN

Hydrostatic extrusion is a modern method of shaping material microstructure and properties. Hydrostatic extrusion can also be successfully used for consolidation of hard magnetic powders. The effect of extrusion temperature, within the range of 700-800°C, on the magnetic properties of the bulk, final product was studied. A commercial MQU-F42 powder, dedicated to hot pressing, was placed in copper capsules and initially cold compacted up to 60% of the theoretical density. Subsequently, the billet was heated in an oven to temperatures 700 and 800°C, respectively and subjected to hydrostatic extrusion. The extruded product had a form of a copper rod, with the Nd-Fe-B core, having 96% of theoretical density (true strain 1.85 after extrusion at 800°C). The extrusion process led to deterioration of the coercivity, for which coarsening of the Nd₂Fe₁₄B grains was blamed. In order to prove this hypothesis, the starting powder was annealed in a temperature range of 550-900°C for various times. The crystallite size, measured after annealing by the X-ray diffraction method, showed that with extension of time and elevation of the temperature the crystallite size increases, however the dominating parameter is the temperature. Correlation of the crystallite size with temperature indicates that when the crystallites are larger than 80 nm the magnetic properties dramatically decrease. Additionally, after HE at 800°C micrometric size Nd-rich phase appear in the microstructure. The Nd is squeezed from the grain boundary of the Nd₂Fe₁₄B phase leading to non-isolated grains, which also contributes to the deterioration of the coercivity.

8

Complex Characteristics of Sintered Nd-Fe-B Magnets in Terms of Hydrogen Based Recycling

51%

Szymański M., Michalski B., Leonowicz M., Miazga Z.

Acta Physica Polonica A

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2017

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vol. 131

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issue 5

1270-1273

EN

Sintered Nd-Fe-B magnets, dismantled by the P.P.H.U. Polblume company from scrap hard disc drives and medical device, were thermally demagnetized and analyzed in terms of their chemical composition, structure and magnetic properties. Magnets from hard disc drives drives had a magnetic structure of two opposite poles in a plane of a magnet and were covered with a nickel coating (around 50 μ m in thick), which however was often discontinuous and deeply scratched. The majority of the magnets were partially destroyed (broken or corroded). The magnet from hard disc drives were basically made of iron (65±1 wt%) and neodymium (30±2 wt%) however, they also included alloying elements such as Co (1-2.5 wt%), Dy (0-1 wt%) or Pr (0-5 wt%). The magnets from medical device consisted only of iron (65±1 wt%) and neodymium (34±1 wt%). Magnets of both kinds were textured thus their XRD patterns were amended. Diffraction patterns, typical for the Nd₂Fe₁₄B (φ) phase, were achieved after mechanical crushing of the bulk magnets. A regular X-ray diffraction pattern was achieved after mechanical crushing of the magnets. The microstructure of both types of the magnets, observed by scanning electron microscopy, consisted of grey grains of a Nd₂Fe₁₄B (φ) phase and a Nd-rich grain boundary phase. The magnets from hard disc drives exhibited excellent magnetic properties and anisotropy: maximum energy product above 300 kJ/m³, remanence around 1.4 T and coercivity around 1000 kA/m, slightly varying between each magnet. Magnetic properties of medical magnet were only a little worse: maximum energy product above 200 kJ/m³, remanence around 1.1 T and coercivity around 900 kA/m. Hydrogen disproportionation phase diagrams (temperature vs. pressure) were constructed for both kinds of the magnets, revealing possible conditions for the hydrogenation, disproportionation, desorption and recombination reaction.

9

The Magnetic Entropy Changes in Pb Doped Ni-Mn-Cu-Ga Alloys

46%

Sielicki K., Zygmuntowicz J., Wróblewski R., Leonowicz M., Sielicki K., Zygmuntowicz J., Wróblewski R., Leonowicz M.

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10

Microstructure and Properties of Magnets Obtained by Hydrostatic Extrusion of Nd-Fe-B Powder

39%

Gizynski T., Kaszuwara W., Pawlik P., Kulczyk M., Leonowicz M., Michalski B.

Acta Physica Polonica A

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2015

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vol. 127

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issue 2

626-628

EN

Nd-Fe-B MQ powder was initially densified in a copper capsule to reach about 60% of the theoretical density. Subsequently, three various processes of hydrostatic extrusion were conducted at room temperature. The values of true strain, obtained during the all three stages, were 1.38, 0.89, 0.94, respectively. The investigation performed showed that the coercivity of the material decreases as the strain increases. Decrease of the remanence was observed only for the highest strains. Size of the particles was strongly reduced during the extrusion processes. X-ray diffraction did not show changes in the phase structure of the material. The Mössbauer study, of the sample extruded within all the three stages, showed existence of the Nd₂Fe₁₄B phase and 16% of other phase. Analysis of magnetization versus temperature confirmed that the additional phase was ferromagnetic.

11

Entropy Change Calculations for Pure Gd and a Ni-Mn-Cu-Ga Heusler Alloy: Constant Field vs. Constant Temperature Experiment

39%

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.

12

Structure and Magnetic Proporties of Polymer Matrix Nanocomposites

33%

Ławecka M., Leonowicz M., Kopcewicz M., Ślawska-Waniewska A., Kozubowski J., Dzhardimalieva G., Rosenberg A., Pomogailo A.

Acta Physica Polonica A

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2002

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vol. 102

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issue 2

317-321

EN

Structure and magnetic properties of the thermal decomposition products of Fe(III)Co(II) acrylate complex were analysed. The crystalline phases, which were found in the fully processed material, at 643 K, were Fe_3O_4, CoFe_2O_4, and CoO and had a mean particle size of about 30 nm. In the intermediate stages of the thermolysis iron was present in a form of Fe^{III} (trivalent low-spin iron), Fe^{2+} (divalent high-spin iron), and Fe_3O_4. The coercivity and remanence were measured versus temperature in the range of 5-300 K, in 1.1 T applied field. Both, _MH_c and M_r, decreased showing room temperature values of 0.038 T and 7.49 mT, for coercivity and remanence, respectively. At temperatures below 200 K the hysteresis loops were asymmetrical, opened and shifted towards negative field values.

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Nanocrystalline Permanent Magnets with Enhanced Properties

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

Magnetocaloric Effect in Ni-Cu-Mn-Gd-Ga Alloy. XI Symposium of Magnetic Measurements

Structure and Properties of Nd-Fe-B Alloy Subjected to HDDR Process

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

Structural and Thermophysical Properties of Magnetic Beads Containing Metallic Nanocrystallites

Consolidation of Nanocrystalline Nd-Fe-B Powder by Hydrostatic Extrusion at High Temperature

Complex Characteristics of Sintered Nd-Fe-B Magnets in Terms of Hydrogen Based Recycling

The Magnetic Entropy Changes in Pb Doped Ni-Mn-Cu-Ga Alloys

Microstructure and Properties of Magnets Obtained by Hydrostatic Extrusion of Nd-Fe-B Powder

Entropy Change Calculations for Pure Gd and a Ni-Mn-Cu-Ga Heusler Alloy: Constant Field vs. Constant Temperature Experiment

Structure and Magnetic Proporties of Polymer Matrix Nanocomposites