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  1. 25 Acta Physica Polonica A

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  1. 9 Zeleňák V.

  2. 9 Zeleňáková A.

  3. 6 Kováč J.

  4. 4 Hrubovčák P.

  5. 4 Kopčanský P.

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1
Content available remote

Manganese Perovskite Nanoparticles and the Downturn of Inverse Susceptibility above the Curie Temperature

100%
Maryško M., Pollert E., Kaman O., Veverka P., Jirák Z.
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issue 5
792-793
EN
In the La_{0.75}Sr_{0.25}MnO_3 nanoparticle system for hyperthermia a downturn in the inverse susceptibility above the Curie temperature T_{c} was observed and interpreted in terms of a finite width of the T_{c} distribution.
2
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Studies on Approximation Methods in Calculating the Magnetic Dipolar Interaction Energy, and Its Impact on the Relaxation Time of Magnetic Nanoparticle Systems

100%
Cacciola M., Berdie A.
Acta Physica Polonica A
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2016
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vol. 129
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issue 1
88-96
EN
The studies on monodomain magnetic nanoparticle systems in colloidal suspensions have heightened lately due to their technological applications, in particular in medicine. Most applications depend on the behaviour of these systems in external magnetic field. In these systems, the nanoparticle dynamics are characterized by the Néel relaxation time and Brownian relaxation time. Due to the complexity of these systems, modelling and numerical simulation, requiring some methods of calculation, are used in the studies. Lately, it has been experimentally and theoretically shown that the magnetic dipolar interactions among nanoparticles influence the behaviour of the systems, even at low concentrations of nanoparticles. The complexity of the problem related to this type of interaction comes from its long-range anisotropic characteristic. This paper presents a series of studies on how the approximation methods, used for the dipolar magnetic interaction energy calculation, affect the magnetic nanoparticle relaxation time, as well as the impact of this aspect on the interpretation of results.
3
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AC Magnetic Susceptibility of Ferrofluids Exposed to an External Electric Field

51%
Rajňák M., Dolník B., Kováč J., Paulovičová K., Mitróová Z., Kurimský J., Cimbala R., Kopčanský P., Timko M.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
887-889
EN
It is known that ferrofluid superparamagnetic nanoparticles response to external magnetic fields, often resulting in the formation of elongated clusters along the field. This has a notable impact on dielectric properties of ferrofluids. Here we report on indications of a contrary effect when the magnetic susceptibility of ferrofluids based on transformer oil is influenced by an external electric field. This effect is associated with structural changes in the ferrofluids induced by the external electric fields. Particularly, we focus on a steady state electric field effect, which gives rise to forces acting on the magnetite nanoparticles, leading to the formation of aggregates. In this condition we have measured the ferrofluid AC magnetic susceptibility in parallel and perpendicular configuration of magnetic and electric fields at room temperature. The measurements in both configurations yielded a noticeable decrease in the real susceptibility values with increasing electric field intensity. The result is believed to be caused by the reduction in the total magnetic moment of the ferrofluid. This can be a consequence of the superspin interactions in the aggregates, minimizing the aggregate's energy. Finally, we highlight the necessity of NMR and small angle scattering of polarized neutrons investigations in order to obtain exact information on the magnetic structure induced by the electric forces.
4
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Role of Oxygen Coordination on the Ultrafast Demagnetization in Ferrite Nanoparticles

51%
Terrier E., Liu Y., Begin S., Pichon B., Bigot J., Halte V.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
345-346
EN
In this work, we have studied the ultrafast dynamics of charges and spins in assemblies of magnetite (Fe₃O₄) and maghemite (γ - Fe₂O₃) nanoparticles. We demonstrate that using time-resolved magneto-optics one is able to disentangle those very similar iron oxide structures. The Fe₃O₄ nanoparticles are elaborated by hydrothermal decomposition and deposited by drop on a glass substrate. γ - Fe₂O₃ nanoparticles assemblies have been obtained by annealing the Fe₃O₄ nanoparticles. Comparing time resolved transmission and Faraday rotation, our measurements show that in case of Fe₃O₄ the demagnetization occurs after the thermalization of the charges, as expected from previous works on ultrafast quenching of magnetization in ferromagnetic nanostructures. On the contrary, in the case of maghemite nanoparticles, an acceleration of the demagnetizing occurs, leading to a simultaneous charges and spins dynamics. We attribute this behavior to the rearrangement of vacancies and annealing of crystal defects in maghemite.
5
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Synthesis and Characterization of Fe_{80}B_{20} Nanoalloys Produced by Surfactant Assisted Ball Milling

51%
Fadaie A., Akdeniz M., Mekhrabov A.
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vol. 125
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issue 2
597-599
EN
In this present study attempts have been made to synthesize Fe_{80}B_{20} crystalline/amorphous nanocomposite powder by using surfactant-assisted high-energy ball milling. Comparison has been made for the differences in evolved microstructure via solidification and solid state phase transformation under equilibrium and non-equilibrium processing conditions. Structural analysis reveal that initially observed Fe_2B and Fe_3B intermetallic phases tend to disappear even at 1 h milling time and eventually lead to the stabilization of α-Fe nanoparticles and possible formation of amorphous phase by increasing milling time. This resultant structure governs the magnetic behaviour of the Fe_{80}B_{20} nanoalloy.
6
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Superparamagnetism in Cobalt Nanoparticles Coated by Protective Gold Layer

51%
Hrubovčák P., Zeleňáková A., Zeleňák V., Kováč J.
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vol. 126
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issue 1
216-217
EN
In this work we present the study on structural and magnetic properties of fine cobalt nanoparticles coated by protective gold layer synthetized by microemulsion method. Structural measurements (powder XRD, HRTEM) confirmed spherical shape of the particles, their nanocrystalline character and presence of individual Co and Au phases. Investigation of magnetic properties of the particles revealed superparamagnetic behavior at higher temperatures and magnetic hysteresis at low temperatures. Average magnetic moment of individual particle m_{p}~86.3μ_{B} was established. The critical temperature, below which the magnetic moments of the particles are blocked, was T_{B}=6 K. Investigation of magnetic relaxation processes via magnetic susceptibility, detected one maximum attributed to single relaxation process, present in the particles. Obtained data, interpreted in terms of Neél-Arrhenius and Vogel-Fulcher theoretical models, confirmed the presence of strong magnetic interparticle interactions.
7
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Ordered Nanoporous Silica Modified with Nanoparticles of Lanthanide Oxides

51%
Zeleňáková A., Kapusta O., Zeleňák V.
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vol. 126
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issue 1
218-219
EN
Lanthanide oxide nanoparticles were encapsulated inside of pores of highly ordered periodic silica of SBA15 type with hexagonal symmetry. The magnetic properties of such nanoperticles were investigated. The structural characterization using the SAXS, XANES, XRD, and N_{2} adsorption measurements showed the presence of lanthanide oxides of Ln_{2}O_{3} type (Ln=La, Pr, Nd, Gd, Eu), with the size of about 5 nm, incorporated in nanoporous channel system. Their magnetic properties, studied by SQUID apparatus, showed the weak antiferromagnetic ordering at 2 K in the nanocomposites Gd_{2}O_{3}@SBA15, Pr_{2}O_{3}@SBA15 and Nd_{2}O_{3}@SBA15. This behaviour of the nanoparticles is caused by blocking process of magnetic moments, which at 300 K exhibit the superparamagnetism, evidenced from ZFC/FC magnetization.
8
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Structure and Magnetic Properties of Three-Dimensional Gadolinium-Based Hybrid Framework

51%
Almáši M., Zeleňáková A., Císařová I., Bednarčík J., Zeleňák V.
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vol. 126
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issue 1
308-309
EN
In the present work we have focused on the preparation and magnetic study of coordination polymer formed by Gd(III) cations as nodes and formate (HCOO¯; FOR) anions as charge compensating linkers. The prepared complex with formula {[Gd(μ_{3}-FOR)_{3}]}_{n} was characterized by single-crystal X-ray diffraction, and high-energy powder X-ray diffraction. The structural study showed that complex is formed by 3D polymeric network with the shortest Gd-Gd, distances of 3.998 Å. The magnetic properties of the complex were studied by magnetic susceptibility χ_{M}(T) and magnetization M(H) measurements. The results show on the weak antiferromagnetic coupling at low temperatures represented by the Weiss constant θ=-0.468 K. The value of effective magnetic moment μ_{eff}=7.57μ_{B}, which was estimated from the experimental data is close to the theoretical value for systems with S=7/2. Correlation between crystal structure of complexes and magnetic properties is presented.
9
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Magnetic Properties of Poly (Divinylbenzene, Ethylene Glycol Dimethacrylate and Vinyl Alcohol) Containing Barium Ferrite Nanoparticles

51%
Gunes S., Akay S., Kara A.
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vol. 125
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issue 2
538-540
EN
Three different kinds of polymer films, poly (divinylbenzene), poly (ethylene glycol dimethacrylate) and poly (vinyl alcohol), containing M-type hexagonal barium ferrites (BaFe12O19) were synthesized on glass substrates by using surface polymerization method. The structural properties were characterized by X-ray diffraction and atomic force microscopy. X-ray diffraction patterns show that polymer films have a polycrystalline structure. The magnetic measurement of polymer films were examined at room temperature using vibrating sample magnetometer and magnetic force microscopy, respectively. The magnetic measurements indicate that P(VA)-BF films exhibit higher saturation magnetization and coercive field than P(EGDMA)-BF and P(DVB)-BF films.
10
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Magnetic and Structural Studies into the Effect of Solvent Exchange Process in Metal-Organic Framework MOF-76(Gd)

51%
Almáši M., Zeleňák V., Zeleňáková A.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
991-993
EN
Effect of solvent exchange/absence on magnetic and structural properties of microporous metal-organic framework MOF-76(Gd) has been performed. Three compounds have been prepared and characterized: as synthesized MOF-76(Gd)-DMF, which containing DMF (N,N'-dimethylformamide) and H₂O molecules in the cavity system, activated complex without solvents, MOF-76(Gd) and water exchanged sample MOF-76(Gd)-H₂O. The structural study showed that compounds undergo structural changes after activation/exchange processes. Changes were mainly observed in the magnetic properties and distances between Gd...Gd ions: 4.718 Å for MOF-76(Gd)-DMF, 4.326 Å for MOF-76(Gd)-H₂O and 4.296 Å for MOF-76(Gd). The magnetic properties of the samples were studied by magnetic susceptibility χ_{M}(T) and magnetization M(H). The low positive value of the Weiss constant, Θ = 1.54 K in compound MOF-76(Gd)-DMF shows on a very weak ferromagnetic interaction. On the contrary, the negative values of Θ in complexes MOF-76(Gd) (-5.58 K) and MOF-76(Gd)-H₂O (-6.23 K) confirm the existence of antiferromagnetic exchange interaction between Gd(III) ions.
11
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Growth of Pt-Ni Nanoparticles of Different Composition using Electrodeposition and Characterization of Their Magnetic Properties

51%
Kožejová M., Hložná D., Hua Liu Y., Ráczová K., Čižmár E., Orendáč M., Komanický V.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
839-841
EN
We prepared Pt₃Ni and PtNi₃ nanoparticles of various sizes on conductive and atomically smooth highly oriented pyrolytic graphite surfaces using potentiostatic electrodeposition. We can control the size of electrodeposited nanoparticles and their density on the surface by changing the deposition time. The morphology of nanoparticles was determined by scanning electron microscopy. PtNi₃ particles have spherical shape, while Pt₃Ni particles have more irregular shape. Composition of particles was confirmed by energy dispersive spectroscopy. We have measured magnetic properties of both systems with 100 s preparation time, superparamagnetic behavior was observed in PtNi₃ nanoparticles with blocking temperature T_{B}=225 K.
12
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Interaction of Magnetic Nanoparticles with Lyotropic Liquid Crystal Studied by AFM

51%
Tomašovičová N., Yang C., Balejčíková L., Gdovinová V., Kubovčíková M., Hayryan S., Hwang I., Hu C.-K., Kopčanský P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
958-960
EN
In this work the interaction of lysozyme fibrils with magnetic particles has been studied by atomic force microscopy. The experiments were carried out for a better understanding of the binding process of such complex soft matter systems. The obtained results show that interaction between lysozyme fibrils and magnetic particles starts immediately after mixing them together. Moreover, the samples remain stable in duration of several days after preparation.
13
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Magnetic-Field Induced Isotropic-Nematic Phase Transition in PDLC Doped with Magnetic Nanoparticles

51%
Mitróová Z., Tomašovičová N., Timko M., Koneracká M., Tomčo L., Jadżyn J., Palewski, T., Kopčanský P., Kovalchuk O.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1299-1301
EN
The paper presents a study of the polymer dispersed liquid crystals that consist of liquid crystal 4-trans-4'-n-hexyl-cyclohexyl-isothiocyanatobenzene (6CHBT) microdroplets dispersed in polyvinyl alcohol and doped with various kinds of magnetic particles. As magnetic nanoparticles there were used single walled carbon nanotubes and magnetite labeled single walled carbon nanotubes. The volume concentration of the particles was 2 × 10^{-3}. Magnetic properties were investigated by a SQUID magnetometer. The higher saturation magnetization has been achieved in sample polymer dispersed liquid crystal doped with magnetite labeled single walled carbon nanotubes. The phase transition temperature from isotropic to nematic phase at the external magnetic field 0 T and 12 T was monitored by precise capacitance measurements in the capacitance cell filled with prepared sample. The significant shift of the phase transition temperature (0.2°C) at the external magnetic field 12 T has been observed in sample polymer dispersed liquid crystal doped with magnetite labeled single walled carbon nanotubes.
14
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AC Magnetic Susceptibility Study of Fe and Co Based Nanoparticles

51%
Zeleňáková A., Kováč J., Zeleňák V.
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vol. 126
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issue 1
222-223
EN
We have investigated magnetic properties of three different samples composed of magnetic Fe or Co core and protective Au or Pt metallic shell, namely Fe@Au, Co@Au and Fe@Pt samples, with sizes of about 10 nm, 8 nm and 5 nm respectively. We have measured and analysed the experimental data of real and imaginary component of ac susceptibility through theoretical laws for non-interacting and interacting particles and we have estimated the strength of their magnetic interactions. Our analyses showed the increase of inter-particle interactions with decreasing particles size.
15
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Effect of 1D Ordering on Magnetic Properties of Iron Nanoparticles coated by Silica Shell

51%
Zeleňáková A., Hrubovčák P., Zeleňák V., Kováč J.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
561-563
EN
Peculiar magnetic properties of 1D arranged composite consisting of Fe nanoparticles coated by insulating SiO2 layer were studied. Silica layer promotes the self-organization of 4 nm iron nanoparticles to the chain-like structures. Magnetization study shows that prepared nanoparticles exhibit very strong inter-particle magnetic interactions, which lead to long-range ordering of nanoparticles magnetic moments. Magnetic properties show superferromagnetic behaviour. The low value of room temperature coercivity, the existence of electrical insulating silica layer and small size of iron nanoparticles favour studied material for potential usage in microelectronic devices designed for high voltage signals modulated by high frequencies.
16
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Magnetic Properties of Fe@Pt Nanoparticles with Core/Shell Morphology

51%
Zeleňáková A., Zeleňák V., Bednarčík J., Lauda M., Kováč J.
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issue 5
1002-1004
EN
We have investigated the magnetic properties of iron nanoparticles coated by platinum shell prepared by chemical procedure. Magnetic measurements using SQUID magnetometer confirm the behaviour typical for a superparamagnetic system. From the M(H) loop at 300 K the magnetic moment of each particle m_{P} ≈ 250 μ_{B} was calculated. The magnetic relaxation study by the in-phase χ' and out-of-phase χ" ac susceptibilities in frequency range 0.1-1000 Hz suggests the existence of two magnetic layers with different magnetic spin's dynamics and strong dipolar interactions between nanoparticles. The observed magnetic behaviour is caused by the blocking process of interacting superparamagnetic particles with magnetic iron core, diamagnetic platinum shell and spin-glass like behaviour magnetic interlayer between them.
17
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Magnetometric Measurements of Low Concentration of Coated Fe_{3}O_{4} Nanoparticles

51%
Škrátek M., Šimáček I., Dvurečenskij A., Majerová M., Maňka J.
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vol. 126
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issue 1
396-397
EN
A modified RF SQUID system with the 2^{nd} order gradiometer has been tested for the purposes of detecting the magnetic nanoparticles as potential carriers of biological medicament. The paper presents basic information about the sensitivity of the system and its use for quantification of low concentration of coated Fe_{3}O_{4} magnetic nanoparticles. Model measurements provided information that enabled us to define the parameter influencing the experimental results. The volume of the biological object and its distance from the antenna appear to have the significant influence on the measurement accuracy.
18
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Effect of BSA Protein on the Contrast Properties of Magnetite Nanoparticles during MRI

51%
Strbak O., Kubovcikova M., Baciak L., Khmara I., Gogola D., Koneracka M., Zavisova V., Antal I., Masarova M., Krafcik A., Kopcansky P., Dobrota D., Frollo I.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1102-1104
EN
The aim of the study was to establish whether there is a significant change in the MRI contrast of magnetite nanoparticles, after BSA protein binding on the surface of particles. The rationale is the applicability of this feature in clinical practice for the tracking of specific proteins which are often associated with various pathologies. Contrast agents could bind to this specific marker, with the change in MRI contrast indicating the presence of pathology. We found that changes in relative contrast acquired at low-field MRI offer potential for the differentiation of magnetite nanoparticles with and without BSA protein. However, the variations in the transverse relaxation time (T₂) and transverse relaxivity (r₂), acquired at high-field MRI, were too small to be applicable for biomedical applications.
19
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Vortex State Suppression in a Hexagonal Array of Interacting Py Triangular Rings

51%
Spizzo F., Patrignani L., Bisero D., Vavassori P., Metlushko V.
Acta Physica Polonica A
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2013
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vol. 123
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issue 2
218-220
EN
We investigate the effect of magnetostatic interactions on the magnetization reversal process of equilateral triangular rings arranged on a hexagonal lattice. Inter-ring interactions originate as rings corners host domain-walls that produce an intense dipolar field; the effect of such interactions is studied by recording hysteresis loops for different magnetic field orientations. Rings magnetic configuration is probed via magnetic force microscopy and diffraction magneto-optic Kerr effect measurements. We observe that the effect of stray fields due to domain-walls competes with that of shape anisotropy, and that the former prevails when the magnetic field orientation is parallel to rings symmetry axes.
20
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Evidence of Formation of Co_{x}Cu_{1-x} Nanoparticles with Core-Shell Structure

51%
Dhara S., Chowdhury R., Bandyopadhyay B.
Acta Physica Polonica A
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2015
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vol. 128
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issue 4
533-535
EN
We have prepared Co_{x}Cu_{1-x} granular alloys with Co contents (x ≈ 0.01-0.30) by chemical reduction. Samples are characterized by X-ray diffraction and transmission electron microscopy yielding particles of mean diameter 8-20 nm formed in fcc phase. The branching in ZFC/FC magnetization behavior confirm superparamagnetism in the samples, characterized by blocking temperature distributions which represent variations in particle size and inhomogeneities of their chemical compositions. Magnetic field dependence of magnetization show hysteresis loops, and the magnetization at any temperature 4-300 K is a combination of ferromagnetism and superparamagnetism. The saturation moment of Co for the ferromagnetism part increases with the Co content. But the coercive fields (H_{C}) and magnetic anisotropy of the particles do not vary with Co concentration. Annealed samples exhibit exchange bias in the range 20-150 Oe at 4 K. The results indicate formation of nanoparticles of CoCu alloy in a core-shell type structure with Co being concentrated near the core.
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