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1
Content available remote

Magnetization Processes of Nanoparticles Embedded into Ferromagnetic Matrix

100%
Ziółkowski G., Chrobak A.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
597-599
EN
The paper refers to computer simulations of interactions between magnetically hard particle embedded into ultra-hard matrix. We used simulated annealing and Monte Carlo simulations in a frame of the 3D Heisenberg model. The performed simulations reveal that the particles show additional exchange anisotropy dependent on "frozen" spin direction in the matrix and the angle between matrix and particle easy magnetization axes. The particle-matrix coupling are responsible for multi-phase magnetic hysteresis shape and exchange-bias like effect.
2
Content available remote

Impact of Antisymmetric Anisotropy on Magnetisation of Ultra-Hard Nanocrystalline Alloys

100%
Ziółkowski G., Chrobak A.
Acta Physica Polonica A
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2016
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vol. 130
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issue 4
1137-1140
EN
This paper describes an application of two-level Stoner-Wohlfarth model including antisymmetric anisotropy and two-level energetic model for simulations of magnetization processes in nanocrystalline, ultra-hard magnetic alloys. The simulation results have been compared with the experimental data obtained for the (Fe₈₀Nb₆B₁₄)_{0.88}Tb_{0.12} alloy. Moreover, the correctness of the proposed model was confirmed by the quantitative agreement with the direct Monte Carlo simulations of similar magnetic systems.
3
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Nanoscale Analysis of Superparamagnetic Systems

100%
Chrobak A., Ziółkowski G.
Acta Physica Polonica A
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2017
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vol. 131
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issue 5
1371-1374
EN
The paper refers to a kind of nanoscale characterization of superparamagnetic materials above and below the so-called blocking temperature. It is propose to apply the Stoner-Wohlfarth model of nanoparticles magnetization supplemented by the two-level kinetic model, determining behavior in T>0. This approach allows determination of distribution of magnetic moments and energetic barriers of magnetic objects based on magnetization curves. In many cases, the determined distribution of magnetic moments can be recalculated into average size of the magnetic objects giving finally a nano/microscaled picture of the material. The proposed method was successfully used in characterization of diluted magnetics, nanocomposites, powders and even for human hemoglobin. In the paper the basic theory and its application to the nanoscale characterization is discussed in detail.
4
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The Crystal and Magnetic Properties of Some Fe-Nb-B-Ni Alloys

100%
Kądziołka-Gaweł M., Chrobak A.
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EN
The crystal and magnetic properties of (Fe₈₀Nb₆B₁₄)_{1-x}Niₓ (x = 0.1, 0.2 and 0.4) bulk alloys prepared by making use of mould casting technique have been studied by X-ray diffraction, magnetostatic and Mössbauer effect methods. Structural and magnetic properties of investigated bulk alloys have been compared with polycrystalline Fe_{1-x}Niₓ (x = 0.1, 0.2 and 0.4) alloys. The measurements have shown that the crystal and magnetic nonhomogeneity for bulk alloys are higher than in polycrystalline compounds, which confirms many magnetic wide magnetic hyperfine field distribution. The mean diameters of crystallites for (Fe₈₀Nb₆B₁₄)_{1-x}Niₓ alloys was calculated from X-ray line broadening and were bigger than 10 nm. The mean magnetic moment and average magnetic hyperfine fields decrease with increase of nickel concentration in investigated compounds.
5
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The Crystal Structure and Magnetic Properties οf Selected fcc FeNi and Fe_{40}Ni_{40}B_{20} Alloys

81%
Kądziołka-Gaweł M., Zarek W., Popiel E., Chrobak A.
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issue 2
412-414
EN
The crystal structure and magnetic properties of polycrystalline alloys Fe_{62.5}Ni_{37.5}, Fe_{60}Ni_{40}, Fe_{50}Ni_{50} obtained by arc-melting and Fe_{40}Ni_{40}B_{20} alloy obtained by melt spinning technique were investigated by X-ray, magnetostatic and Mössbauer effect methods. The X-ray measurements show that Fe_{40}Ni_{40}B_{20} alloy has a face-centered structure (fcc) which means that boron did not cause an amorphous rendering. The lattice constants for this alloy (a = 3.53 Å) is smaller than for FeNi alloys (a > 3.57 Å) which suggests that boron atoms were built-in in the crystal lattice. The Curie temperature of this alloy is more than 150 K higher in comparison with the of FeNi alloys, but the magnetic moment connected with this alloy is more than 0.17 μ_{B}/atom smaller than the magnetic moments of FeNi alloys. The shape of hyperfine field distribution for Fe_{40}Ni_{40}B_{20} is similar to the shape of hyperfine field distribution for the investigated fcc Fe_{62.5}Ni_{37.5} alloy, but both are different from another investigated hyperfine field distribution of FeNi alloys.
6
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Structural and Magnetic Properties of Dy(Fe,V,Si)_{12} Compounds

81%
Drzazga Z., Winiarska A., Chrobak A., Kaczorowski D.
Acta Physica Polonica A
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1997
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vol. 92
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issue 2
335-339
EN
An influence of Si on the structural and magnetic properties of Dy(Fe,V,Si)_{12} compounds is studied. X-ray diffraction shows that these materials crystallise in the tetragonal ThMn_{12}-type structure. An increase in the saturation magnetization, the Curie temperatures and magnetocrystalline anisotropy in the Si substitutional systems is observed when compared with DyFe_{12-x}V_{x}. The magnetic properties depend on the preferential site occupation and concentration of Si and V atoms in these compounds.
7
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Magneto-History Effect in the Tb_{x}Gd_{1-x}Ni_3 Compounds

81%
Bajorek A., Chełkowska G., Chrobak A., Kwiecień-Grudziecka M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1136-1138
EN
The compounds Tb_{x}Gd_{1-x}Ni_3 with a PuNi_3-type structure have been obtained. The magnetic properties have been investigated by using SQUID magnetometer (Quantum Design MPMS, temperature from 1.9 K to 300 K and magnetic field up to 7 T). The partial replacement of Gd by Tb atoms is reflected in a decrease of the ordering temperature from 115 K (x = 0.0) to 81 K (x=1.0) as well as the increase of the saturation magnetic moment M_{S} from 6.93 μ_{B}/f.u. (x=0.0) to 7.14 μ_{B}/f.u. (x=1.0). A large difference of M(T) curves has been noticed between the so-called field cooling-zero field cooling magnetization. The thermomagnetic curves are sensitive to the applied magnetic field and their origin can be understood as the domain-wall pinning effect and as the temperature dependence of coercivity.
8
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Electrical Resistivity and Electronic Structure of the Tb_{x}Gd_{1-x}Ni_3 System

81%
Chełkowska G., Bajorek A., Chrobak A., Kwiecień-Grudziecka M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1139-1141
EN
In the paper the electric properties and electronic structure of the intermetallic Tb_{x}Gd_{1-x}Ni_3 compounds are presented. The partial replacement of Gd by Tb atoms causes the decrease of the Curie temperature (T_{C}) and the increase of the residual resistivity. According to the Matthiessen rule the scattering mechanisms in ρ(T) have been analyzed. Moreover, the reduced form of the electrical resistivity ρ_{Z} (T - T_{0}) indicates a deviation from the linearity for x > 0.2. This kind of behaviour can be attributed to density of d states near by the Fermi level (E_{F}) which are dominated by Ni 3d states. The valence band spectra as well as the core level lines have been analyzed as the influence of Tb/Gd substitution on the electronic structure.
9
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Effect of Tb/Gd Substitution on Crystal Structure and Exchange Interactions of Gd_{1 - x}Tb_{x}Ni_3 Intermetallic Compounds

81%
Chrobak A., Bajorek A., Chełkowska G.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1132-1135
EN
In the paper an influence of Tb/Gd substitution on crystal structure and exchange interactions of Gd_{1 - x}Tb_{x}Ni_3 (x = 0.0, 0.5, 0.8, 1.0) polycrystalline compounds have been studied. The crystal structure of all samples was checked at the room temperature by means of X-ray diffraction. Exchange integrals of R-R (J_{RR}), T-T (J_{TT}) and R-T (J_{RT}) atoms were evaluated from M(T) magnetization curves (2-300 K, 2 T) based on the mean field theory calculation. As it was shown the samples examined are single phase and crystallize in the PuNi_3 (space group R-3m) type of crystal structure. The Tb/Gd substitution causes the decrease of lattice parameters as well as the volume of the unit cell. With increase of the x parameter the magnetic moment of Tb atoms increases from 6.94 μ_{B} (x = 0.5) to 8.12 μ_{B} (x = 1). The M(T) dependence of the examined compounds depends almost 8 times stronger on exchange interactions within the R-R site than the interactions between the two antiferromagnetically coupled magnetic sublattices R-T.
10
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Magnetization Processes of Hard Magnetic Composites - Monte Carlo Studies aum

81%
Ziółkowski G., Granek K., Chrobak A.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
663-665
EN
In the present work we performed some simulated annealing plus Monte Carlo studies concerning a hard magnetic spherical particles embedded into soft ferromagnetic matrix as well as irregular branches of soft and hard magnetic phases. Magnetization process of such system depends on exchange interactions of soft and hard magnetic object and interface between them. Especially interesting is the comparison of interactions in systems with different, regular and irregular geometry.
11
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Phase Structure and Magnetic Properties of Fe-Nb-B-Pt Type of Bulk Nanocrystalline Alloys

81%
Ziółkowski G., Chrobak A., Randrianantoandro N., Klimontko J.
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vol. 126
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issue 1
174-175
EN
The paper refers to magnetic and structure properties of the (Fe_{80}Nb_{6}B_{14})_{1-x}Pt_{x} (x=0.15, 0.3, 0.4 and 0.6) bulk nanocrystalline alloys prepared using the vacuum suction casting technique. The samples were in the form of rods with diameters ranging from 0.5 mm to 1.5 mm. It was shown that the optimal Pt content is x=0.4 with the coercive field equal to 0.2 T and maximum energy product |BH|_{max}=11.2 kJ/m^{3}. The magnetic properties can be associated with Fe-Pt, Fe and Fe-B phases, depending on the alloy composition.
12
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Phase Stability of (Fe_{80}Nb_{6}B_{14})_{0.9}Tb_{0.1} Bulk Nanocrystalline Magnet

81%
Chrobak A., Ziółkowski G., Randrianantoandro N.
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vol. 126
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issue 1
176-177
EN
The paper refers to phase stability of the (Fe_{80}Nb_{6}B_{14})_{0.9}Tb_{0.1} bulk nanocrystalline alloys prepared using the vacuum suction casting technique. The samples were in the form of rods with diameters d=2, 1.5, 1 and 0.5 mm. Heating up to 900 K reveals structural changes that occur at temperatures above 680 K (DSC and M(T) measurements). The phase analysis, using Mössbauer spectra, indicates the decrease of Tb_{2}Fe_{14}B and increase of Fe content in the samples after the heat treatment. The most stable is the alloy with d=1 mm, where the formation of α-Fe phase was not observed. The decrease of d causes significant hardening i.e. coercive field increases from 0.57 T to 2.66 T for d=2 mm and d=0.5 mm, respectively.
13
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Influence of Cooling Rate on Magnetic Properties of (Fe_{80}Nb_{6}B_{14})_{1-x}Tb_{x} Type of Bulk Nanocrystalline Alloys

81%
Chrobak A., Ziółkowski G., Haneczok G.
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vol. 126
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issue 1
178-179
EN
The paper refers to magnetic properties of the (Fe_{80}Nb_{6}B_{14})_{1-x}Tb_{x} (x=0.06 and x=0.08) bulk nanocrystalline alloys prepared using the vacuum suction casting technique. The samples were in the form of rods with diameters of d=1.5 mm, 1 mm and 0.5 mm. It was shown that for the alloys with x=0.08 the significant magnetic hardening with the decrease of sample diameter was observed. For d=0.5 mm the coercive field equals 2.46 T and the maximum energy product |JH|_{max}=77.2 kJ/m^{3}.
14
Publication available in full text mode
Content available

Magnetic properties of polymer matrix composites filled with ferrite powders

81%
Stabik J., Chrobak A., Haneczok G., Dybowska A.
Archives of Materials Science and Engineering
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2011
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vol. 48
15
Content available remote

Effect of the Boron Addition on the Structure of the Ni-Mn-Co-In Alloys

71%
Prusik K., Matyja E., Zubko M., Kubisztal M., Chrobak A.
Acta Physica Polonica A
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2016
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vol. 130
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issue 4
1023-1025
EN
Series of Ni_{45.5-x}Co_{4.5}Mn_{36.6}In_{13.4}B_{x} (at.%, x=0, 0.05, 0.1, 0.5, 1.0) polycrystalline magnetic shape memory alloys produced by the induction melting were examined in terms of the structure and transition temperatures. The structure of the alloys was determined by the X-ray diffraction and transmission electron microscopy. Scanning electron microscopy and electron backscattering diffraction techniques were applied to obtain the microstructure and texture of alloys. Boron addition promotes nucleation of the second Co-rich and In-poor phase as well as causes decrease of the martensitic transformation temperatures.
16
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Magnetic Properties of Tb(Ni_{1-x}Fe_{x})_{3} (x=0.2, 0.6) Crystalline Compounds and Powders

71%
Ociepka K., Bajorek A., Chrobak A., Chełkowska G., Prusik K.
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vol. 126
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issue 1
180-181
EN
In the paper we present and discuss magnetic properties of the Tb(Ni_{1-x}Fe_{x})_{3} (x=0.2, 0.6) crystalline compounds and their ball-milled powders. The investigated samples are polycrystalline and crystallize in the rhombohedral PuNi_{3} type of crystal structure. The Curie temperature of the material seems to be independent of particle size and is constant. The coercivity depends on the amount of iron dopant. The saturation magnetization decreases after mechanical grinding which is connected with the reduction in particle size. After 6 h milling time the SEM results show the presence of nanoflakes with thickness up to 100 nm or even smaller. Moreover, the pulverization leads to the observed decrease of magnetocaloric effect.
17
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Content available

Ferroelectric–Ferromagnetic Composites Based on PZT Type Powder and Ferrite Powder

71%
Bochenek D., Niemiec P., Ziółkowski G., Zachariasz R., Chrobak A.
Archives of Metallurgy and Materials
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2013
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issue 4
18
Content available remote

The Electronic and Magnetic Properties οf Yb_xGd_{1-x}Ni_5 Systems

71%
Szajek A., Werwiński M., Chełkowska G., Bajorek A., Chrobak A.
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issue 5
905-906
EN
The intermetallic compounds Yb_{x}Gd_{1 - x}Ni_5 crystallize in the hexagonal CaCu_5-type structure. Based on wide ranging SQUID-type magnetometer, it was shown that the saturation magnetization decreases with growing concentration of ytterbium. The opposite tendency was observed for the Sommerfeld coefficient obtained in the heat capacity measurements. These results are confirmed using ab initio band structure calculations.
19
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Content available

Optimization of Soft Magnetic Properties in Fe-B and Fe-B-Si Amorphous Alloys Obtained by Melt Spinning Method

71%
Kwapuliński P., Stokłosa Z., Chrobak A., Rasek J., Haneczok G.
Acta Physica Polonica A
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2002
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vol. 102
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issue 2
309-316
EN
In the present paper the process of optimization of soft magnetic properties have been studied by applying different experimental techniques (magnetic measurements, electric measurements, X-ray analysis, and high-resolution electron microscopy observations). It has been shown that an increase in magnetic permeability after optimization annealing can be mainly attributed to annealing out of microvoids.
20
Content available remote

Size Effect of Hard Magnetic Properties of Fe-Nb-B-Tb Milled Alloys

71%
Granek K., Ziółkowski G., Chrobak A., Klimontko J., Talik E.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
645-647
EN
The paper refers to magnetic and structural properties of powders made of Fe-Nb-B-Tb ultra-high coercive alloy. The initial alloy was milled in a low energy mill for 1 h and 14 h. With increasing milling time we observed gradual deterioration of hard magnetic properties i.e. the coercive field decreases from 5.51 T to 0.14 T for the bulk alloy and 14 h milled powder, respectively. However, for the 1 h milling time the micrometric powder reveals quite high coercivity of 2.77 T which is promising for possible applications in magnetic composites.
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