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1

Magnetocaloric Effect in NiCl₂(bipy) at Low Temperatures

100%

Ráczová K., Čižmár E., Feher A.

Acta Physica Polonica A

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2017

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vol. 131

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issue 4

922-924

EN

Magnetothermal properties of the compound NiCl₂(bipy), where bipy = 4,4'-bipyridine, were studied. The single-ion anisotropy of Ni(II) ions was estimated and its influence on magnetocaloric effect in NiCl₂(bipy) was investigated. Above the metamagnetic transition a maximum in the isothermal change of the magnetic entropy is reached near 11 K at field change from 0T to 7T with peak value -ΔS = 6J K¯¹ kg¯¹. The temperature dependence of ΔS above 7K agrees with the assumed easy-axis type of single-ion anisotropy. The inverse magnetocaloric effect, typical for ordered antiferromagnets, was observed in the ordered state of NiCl₂(bipy) only for isothermal magnetization in small fields up to 2T.

2

The Magnetocaloric Effect in {[Cu(bapa)]₃[Cr(CN)₆]₂}ₙ · 6n H₂O at Low Temperatures

100%

Ráczová K., Vavra M., Hegedüs M., Čižmár E.

Acta Physica Polonica A

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2018

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vol. 133

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issue 3

429-431

EN

The crystals of {[Cu(bapa)]₃[Cr(CN)₆]₂}ₙ·6nH₂O (bapa = bis(3-aminopropyl)amine) are formed by infinite Cu(II)-Cr(III) antiparallel chains, which are connected into the third direction by additive [Cu(bapa)] moieties. The onset of long-range magnetic order at 3.2 K was observed by AC susceptibility. The study of the magnetocaloric effect from magnetization measurements yields a large entropy change -ΔS_{M} = 13.65 J K¯¹mol¯¹ (-ΔS_{M} = 12.25 J kg¯¹K¯¹) at the field change from 0 T to 3 T at temperature 4 K. The analysis of the critical behavior of -ΔS_{M} suggests the value of critical exponent n = 0.577 at the ordering temperature characteristic for three-dimensional magnets with Ising anisotropy.

3

EPR Spectra of the Genuine-Organic and Metal-Organic TCNQ-Based Anion Radical Salts

100%

Botko M., Čižmár E., Kajňaková M., Feher A.

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vol. 126

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issue 1

252-253

EN

We have measured the electron paramagnetic resonance spectra of genuine-organic anion-radical salts [Me-2,6-di-Me-Py](TCNQ)_{2}, [Me-3,5-di-Me-Py](TCNQ)_{2}, [N-Me-OH-Me-Py](TCNQ)_{2}, [N-Et-OH-Me-Py](TCNQ)_{2}, and metal-organic anion-radical salt [Mn-phen_{3}](TCNQ)_{2}·H_{2}O in the temperature range from 2 K to 300 K in the X-band frequency range. A comparison study of the shape of spectra, g-factors and linewidths with respect to the composition and crystal structure of studied compounds is presented. While the genuine-organic anion-radical salts display a typical EPR response originating from TCNQ pairs, the spectra of metal-organic anion-radical salt are dominated by the contribution of transition metal.

4

Magnetic Specific Heat of Anion-Radical Salt [Ni(bipy)₃](TCNQ)₄·(CH₃)₂CO at Very Low Temperatures

88%

Šoltésová D., Čižmár E., Vasylets G., Starodub V., Feher A.

Acta Physica Polonica A

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2017

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vol. 131

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issue 4

925-927

EN

Thermodynamic studies of the anion-radical salt system [Ni(bipy)₃](TCNQ)₄·(CH₃)₂CO, where TCNQ is 7,7',8,8'-tetracyano-quinodimethane, are reported. The anion-radical salt systems based on TCNQ belong to a material class in which the arrangement of the anion-radical salt has considerable impact on the charge transfer and magnetic properties. The crystal structure of the studied compound consists of [Ni(bipy)₃]⁺² cations containing Ni⁺² ions and four types of crystallographically independent anion-radicals TCNQ^{·-} (A, B, C and D). These TCNQ^{·-} radicals form two different types of TCNQ^{·-} stacks (AABB and CCDD), where a strong exchange interaction is expected. The temperature dependence of the specific heat of a single crystal was studied in magnetic fields up to 5 T and in the temperature range from 0.4 K to 30 K. The temperature dependence of specific heat displays a broad Schottky-like maximum above 0.4 K. Using a single-ion approximation, the analysis of the temperature dependence of the specific heat below 10 K yields values for the anisotropy parameters, D/k_{B}=-1.95 K and E/k_{B}=0.3 K. These results suggest that the observed maximum in the specific heat originates from Ni⁺² ions while the exchange interaction between the transition metal ions and the TCNQ is negligible.

5

Observation of Anisotropic Exchange in a Spin Ladder by ESR

88%

Čižmár E., Ozerov M., Krämer K., Rüegg C., Zvyagin S.

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vol. 126

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issue 1

238-239

EN

We report on high resolution X-band electron spin resonance (ESR) spectroscopy studies of the spin-ladder material (C_{5}H_{12}N)_{2}CuBr_{4}. Our experiments provide a direct evidence for the presence of anisotropy in (C_{5}H_{12}N)_{2}CuBr_{4} in contrast to a fully isotropic spin-ladder model employed for this system previously. Low-temperature angular dependence of ESR transitions is analyzed employing a simple spin-1/2 dimer model with the symmetric anisotropic exchange interaction.

6

Spin Glass State in S=3/2 Kagomé Antiferromagnet Co(N_{3})_{2}(bpg)[(CH_{3})_{2}(NCOH)]_{4/3}

88%

Vrábel P., Čižmár E., Orendáčová A., Gao S., Orendáč M.

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vol. 126

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issue 1

266-267

EN

Specific heat, magnetic susceptibility and magnetization of Co(N_{3})_{2}(bpg)[(CH_{3})_{2}(NCOH)]_{4/3}, representing S=3/2 kagomé system are reported. Long-range ordering at 16 K was revealed, however, at lower temperatures slow spin dynamics is still found. The analysis of alternating susceptibility suggests the onset of glassy state. The study of the time dependence of magnetization revealed the existence of more relaxation channels with pronounced different relaxation times. The observed behaviour is consistent with the formation of topological spin glass in which relaxation is governed by both spin and chiral degrees of freedom.

7

Spin-Peierls Transition in (N-Me-Tetra-Me-Pz)(TCNQ)_{2}

88%

Kajňaková M., Botko M., Starodub V., Čižmár E., Feher A.

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vol. 126

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issue 1

254-255

EN

The new organic anion-radical salt (N-Me-Tetra-Me-Pz)(TCNQ)_{2}, (Pz = pyrazine) was studied as a low dimensional magnetic system. Heat capacity and EPR studies were performed in the temperature range from 2 to 300 K. The magnetic susceptibility was measured in the temperature range from 2 to 300 K and in magnetic fields of 100 mT and 1 T. The magnetic properties of this new system can be described as a dimerized Heisenberg spin S=1/2 chain possessing a spin-Peierls transition at 42 K.

8

Frustrated Zig-Zag Spin Chains Formed by Hydrogen Bonds in [Cu(H₂O)(OH)(tmen)]₂[Pd(CN)₄]·2H₂O

76%

Čižmár E., Orendáčová A., Orendáč M., Kuchár J., Feher A., Park J., Meisel M.

Acta Physica Polonica A

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2017

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vol. 131

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issue 4

940-942

EN

The magnetic properties of the novel dimeric compound [Cu(H₂O)(OH)(tmen)]₂[Pd(CN)₄]·2H₂O (tmen=N,N,N',N'-tetramethylethylenediamine) with modulated crystal structure were studied in the temperature range from 95 mK to 300 K. Magnetic measurements revealed a presence of weak antiferromagnetic exchange coupling in the compound. The temperature dependence of specific heat is characterized by the presence of a Schottky-like maximum at 0.47 K and a λ-anomaly at 0.28 K, indicating the formation of long-range order in the system. The comparison of the experimental data with theoretical predictions revealed the presence of antiferromagnetic intradimer exchange coupling J/k_{B}= -1.2 K and interdimer coupling of a similar strength mediated via hydrogen bonds between dimeric units forming a frustrated magnetic zig-zag chain structure.

9

Growth of Pt-Ni Nanoparticles of Different Composition using Electrodeposition and Characterization of Their Magnetic Properties

76%

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.

10

Application of Superconductor/Photosemiconductor Contact Structures in Electronics

76%

Bunda V., Bunda S., Komanicky V., Botko M., Čižmár E., Feher A.

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vol. 126

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issue 1

362-363

EN

In recent years, two-dimensional (2D) nanostructured materials, such as nanoplates and nanosheets, have attracted much attention because of their unique electronic, magnetic, optical, and catalytic properties, which mainly arise from their large surface areas, nearly perfect crystallinity, structural anisotropy, and quantum confinement effects in the thickness. The 2D nanostructured materials can be used as building blocks for advanced materials and devices with designed functions in areas as diverse, as lasers, transistors, catalysis, solar cells, light emission diodes, chemical and biological sensors. We report physical properties of YBCO/BiOI contact structures and electrophysical properties of BiOI single crystal.

11

Experimental Study of the Magnetocaloric Effect in Ni(en)(H₂O)₄SO₄·2H₂O - An S = 1 Molecular Magnet with Easy-Plane Anisotropy

76%

Tarasenko R., Orendáčová A., Čižmár E., Orendáč M., Potočňák I., Feher A.

Acta Physica Polonica A

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2017

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vol. 131

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issue 4

904-906

EN

Magnetocaloric properties of Ni(en)(H₂O)₄SO₄·2H₂O powder were investigated in temperature range from 2 K to 30 K in magnetic fields up to 7 T using isothermal magnetization measurements. The maximum value of the isothermal entropy change in the field 7 T is about 8 J/(kg K), with a refrigerant capacity of 55 J/kg. Temperature dependence of the isothermal entropy change under different magnetic fields is in good agreement with theoretical predictions from crystal electric field parameters.

12

EPR Study of the Two-Dimensional Quantum System Cu(en)(H_2O)_2SO_4

76%

Tarasenko R., Orendáčová A., Čižmár E., Orendáč M., Zvyagin S., Wosnitza J.

Acta Physica Polonica A

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2012

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vol. 121

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issue 5-6

1095-1097

EN

The angular dependence of electron paramagnetic resonance spectra of Cu(en)(H_2O)_2SO_4 single crystals was studied in the X-band frequency range at temperatures 4 and 300 K. Analysis of the linewidth at 300 K revealed nice agreement with the angular variation of the g-factor. This coincidence is the manifestation of the symmetric and antisymmetric exchange coupling, as main broadening mechanisms in Cu(en)(H_2O)_2SO_4 at high temperatures. The radical change of the angular dependence of the linewidth observed at 4 K can be ascribed to dipolar coupling.

13

Magnetic Field Induced Slow Magnetic Relaxation in KEr(MoO₄)₂

64%

Tkáč V., Orendáčová A., Tarasenko R., Pajerowski D., Čižmár E., Orendáč M., Anders A., Meisel M., Feher A.

Acta Physica Polonica A

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2015

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vol. 127

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issue 2

353-355

EN

The spin dynamics of a layered magnetic insulator, KEr(MoO₄)₂, have been investigated in a magnetic field applied along the easy axis at temperatures where the magnetism is dominated by the occupation of a ground doublet. More specifically, the DC magnetization and AC susceptibility were studied in magnetic fields up to 5 T and at temperatures ranging from 1.8 to 20 K. The temperature dependence of the AC susceptibility suggests a slowing down of magnetic relaxation with increasing magnetic field. The magnetic field dependence of the AC susceptibility, studied at nominally 2 K, indicates the presence of low-field, intermediate-field, and high-field regimes characterized by the interplay of internal and external magnetic fields that give rise to different relaxation processes.

14

CuBr_2(C_{10}H_8N_2) - S = 1/2 Two-Dimensional Rectangular Heisenberg Antiferromagnet

64%

Čižmár E., Kajňaková M., Orendáčová A., Orendáč M., Feher A., Anders A., Park J., Meisel M.

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issue 5

973-974

EN

Magnetic susceptibility and X-band electron spin resonance study of a two-dimensional Heisenberg antiferromagnetic system CuBr_2(bipy), where bipy = C_{10}H_8N_2 is 4,4'-bipyridyl, has been performed in the temperature range from 300 K down to 2 K. A rhombic anisotropy of the g-factor was obtained from X-band EPR measurements with g_{x} = 2.037, g_{y} = 2.100 and g_{z} = 2.219. The temperature dependence of the magnetic susceptibility with a round maximum observed at 28 K suggests antiferromagnetic type of short-range order. No signature of the magnetic long-range order in studied compound was observed. The comparison of the magnetic susceptibility data with a two-dimensional rectangular Heisenberg model yields the values of intralayer exchange couplings J/k_{B} = - 47 K and J'/k_{B} = - 9.4 K.

15

Magnetic Response of Mn(III)F(salen) at Low Temperatures

52%

Park J., Risset O., Shiddiq M., Peprah M., Knowles E., Andrus M., Beedle C., Ehlers G., Podlesnyak A., Čižmár E., Nagler S., Hill S., Talham D., Meisel M.

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vol. 126

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issue 1

228-229

EN

The low temperature magnetic response of Mn(III)F(salen), salen = H_{14}C_{16}N_{2}O_{2}, an S=2 linear-chain system, has been studied. Using a single crystal with the field applied perpendicular to the chain direction, torque magnetometry, down to 20 mK and up to 18 T, revealed a feature at 3.8 T when T ≤ 400 mK. ESR ( ≈200 GHz) studies, using single crystals at 4 K and in 5 T, have not detected any signal. In 10 mT, the temperature dependence of the susceptibility of powder-like samples can be reasonably fit when J/k_{B}=50 K and g=2. In addition, these data are unchanged for P ≤1.0 GPa. Using a randomly-oriented, powder-like, deuterated (12 of 14 H replaced by D) sample of 2.2 g at 270 mK, neutron scattering data, acquired with the Cold Neutron Chopper Spectrometer at the Spallation Neutron Source, show several well defined excitations that may be from the zero-field energy levels of antiferromagnetic S=2 spins with g=2, J/k_{B}=50 K, D/k_{B}=2.8 K, and E/k_{B}=0.5 K.

16

Neutron and EPR Study of Cu(tn)Cl_{2} - a~Two-Dimensional Spatially Anisotropic Triangular-Lattice Antiferromagnet

52%

Tarasenko R., Orendáčová A., Čižmár E., Maťaš S., Orendáč M., Zeleňák V., Pavlík V., Siemensmeyer K., Zvyagin S., Wosnitza J., Feher A.

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vol. 126

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issue 1

232-233

EN

We have studied the temperature dependence of the lattice parameters and the influence of spin anisotropy on the electron paramagnetic spectra of Cu(tn)Cl_2, an S=1/2 quasi-two-dimensional spatially-anisotropic triangular-lattice Heisenberg antiferromagnet. The variation of the resonance fields with temperature reflects the presence of an easy-plane exchange anisotropy with J_{z}/J_{x,y}<1 and g-factor anisotropy, g_{z}/g_{x,y}>1.

17

Magnetic Properties of the Bi_{0.65}La_{0.35}Fe_{0.5}Sc_{0.5}O₃ Perovskite

52%

Fedorchenko A., Fertman E., Desnenko V., Kotlyar O., Čižmár E., Shvartsman V., Lupascu D., Salamon S., Wende H., Salak A., Khalyavin D., Olekhnovich N., Pushkarev A., Radyush Y., Feher A.

Acta Physica Polonica A

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2017

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vol. 131

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issue 4

1069-1071

EN

Magnetic properties of polycrystalline multiferroic Bi_{0.65}La_{0.35}Fe_{0.5}Sc_{0.5}O₃ synthesized under high-pressure (6 GPa) and high-temperature (1500 K) conditions were studied using a SQUID magnetometer technique. The temperature dependent static magnetic moment M was measured in both zero-field-cooled and field-cooled modes over the temperature range of 5-300 K in low magnetic field H=0.02 kOe. The field dependent magnetization M(H) was measured in magnetic fields up to 50 kOe at different temperatures up to 230 K after zero-field cooling procedure. A long-range magnetic ordering of the antiferromagnetic type with a weak ferromagnetic contribution takes place below T_{N} ≈ 220 K. Magnetic hysteresis loops taken below T_{N} show a huge coercive field up to H_{c} ≈10 kOe, while the magnetic moment does not saturate up to 50 kOe. A strong effect of magnetic field on the magnetic properties of the compound has been found. Below T_{N} ≈220 K the derivatives of the initial magnetization curves demonstrate the existence of a temperature-dependent anomaly in fields of H=15÷25 kOe. The nature of the anomaly is unknown and requires additional study.

Refine search results

Magnetocaloric Effect in NiCl₂(bipy) at Low Temperatures

The Magnetocaloric Effect in {[Cu(bapa)]₃[Cr(CN)₆]₂}ₙ · 6n H₂O at Low Temperatures

EPR Spectra of the Genuine-Organic and Metal-Organic TCNQ-Based Anion Radical Salts

Magnetic Specific Heat of Anion-Radical Salt [Ni(bipy)₃](TCNQ)₄·(CH₃)₂CO at Very Low Temperatures

Observation of Anisotropic Exchange in a Spin Ladder by ESR

Spin Glass State in S=3/2 Kagomé Antiferromagnet Co(N_{3})_{2}(bpg)[(CH_{3})_{2}(NCOH)]_{4/3}

Spin-Peierls Transition in (N-Me-Tetra-Me-Pz)(TCNQ)_{2}

Frustrated Zig-Zag Spin Chains Formed by Hydrogen Bonds in [Cu(H₂O)(OH)(tmen)]₂[Pd(CN)₄]·2H₂O

Growth of Pt-Ni Nanoparticles of Different Composition using Electrodeposition and Characterization of Their Magnetic Properties

Application of Superconductor/Photosemiconductor Contact Structures in Electronics

Experimental Study of the Magnetocaloric Effect in Ni(en)(H₂O)₄SO₄·2H₂O - An S = 1 Molecular Magnet with Easy-Plane Anisotropy

EPR Study of the Two-Dimensional Quantum System Cu(en)(H_2O)_2SO_4

Magnetic Field Induced Slow Magnetic Relaxation in KEr(MoO₄)₂

CuBr_2(C_{10}H_8N_2) - S = 1/2 Two-Dimensional Rectangular Heisenberg Antiferromagnet

Magnetic Response of Mn(III)F(salen) at Low Temperatures

Neutron and EPR Study of Cu(tn)Cl_{2} - a~Two-Dimensional Spatially Anisotropic Triangular-Lattice Antiferromagnet

Magnetic Properties of the Bi_{0.65}La_{0.35}Fe_{0.5}Sc_{0.5}O₃ Perovskite