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1
Content available remote

Paramagnetism of Cu_3RE_2W_4O_{18} Semiconductors (RE = Gd, Dy-Er)

100%
Groń T., Tomaszewicz E., Duda H., Mazur S.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
885-887
EN
Cu_3RE_2W_4O_{18} tungstates (RE = Gd, Dy-Er) are paramagnets in the temperature range 4.2-300 K visible also in the absence of the energy losses in the curve of the imaginary part of magnetic susceptibility, χ". The negative values of the paramagnetic Curie-Weiss temperature, θ, may suggest the weak antiferromagnetic coupling below 4.2 K. The temperature independent component of magnetic susceptibility has a positive value indicating a domination of the Van Vleck contribution. Calculations of the effective number of the Bohr magnetons revealed that the orbital contribution to the magnetic moment comes mainly from the RE^{3+} ions.
2
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Structural Characterization and Magnetic Properties of CuCr₂Te₄ Spinel Obtained by Mechanical Alloying and Heat Treatment

88%
Karolus M., Maciążek E., Panek J., Kubisztal M., Groń T.
Acta Physica Polonica A
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2016
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vol. 130
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issue 4
859-861
EN
CuCr₂Te₄ can be obtain by mechanical alloying followed by heat treatment. The obtained phase crystallizes in the spinel-type structure of the space group Fd3m. The calculated crystallite size equals to 100 nm. Magnetic susceptibility measurements showed ferrimagnetic order below 21 K.
3
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Influence of Cr-Substitution on the Electrical Properties of Fe_{1-x}Cr_{x}SnSbO₆

88%
Groń T., Dąbrowska G., Filipek E., Duda H., Sawicki B.
Acta Physica Polonica A
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2016
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vol. 129
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issue 1a
A-153-A-156
EN
Fe_{1-x}Cr_xSnSbO₆ solid solution shows semiconducting behaviour with the activation energy decreasing from E_{A}=0.64 eV for x=0.0 to E_{A}=0.32 eV for x=1.0 in the intrinsic conductivity temperature region as well as the n-type conduction at room temperature. The I-V characteristics and the conductance G at 300 and 400 K showed symmetrical and nonlinear behavior in the voltage range (-100, 100 V) suggesting the electron emission over the potential barrier especially for the boundary compounds FeSnSbO₆ and CrSnSbO₆. These effects are discussed in the context of the energy gap E_{g}>1.6 eV many times greater than the thermal energy kT.
4
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Influence of Cr-Substitution on the Electrical Properties of Fe_{1-x}Cr_xVSbO_6

88%
Duda H., Filipek E., Dąbrowska G., Groń T., Mydlarz T.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
833-835
EN
Fe_{1-x}Cr_xVSbO_6 solid solution is semiconductor with the activation energy decreasing both in the intrinsic and extrinsic conductivity temperature regions as the Cr-content increases. The n-type conduction is observed for Fe-richer samples while a change of the Seebeck coefficient (from n to p) - for Cr-richer ones. Magnetic isotherms for all samples of solid solution under study are characteristic of the universal Brillouin function, indicating paramagnetic response. These effects are discussed within the framework of the appearance of the mixed valence of both Fe and Cr ions.
5
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Electrical Transport Properties of Yb_{8-x}Y_xV_2O₁₇ (x=0,2,8)

88%
Sawicki B., Piz M., Filipek E., Groń T., Duda H.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
363-366
EN
The UV-vis-NIR and electrical properties of Yb_{8-x}Y_xV_2O₁₇ for x=0, 2, and 8 were investigated. The band energy gap of 2.6 eV determined for Yb_6Y_2V_2O₁₇ (x=2) and comparable for the remaining compounds with x=0 and 8 is characteristic for insulators. Low electrical conductivity with a characteristic minimum shifting to higher temperatures from 322, via 360 to 370 K in the sequence x=0, 2 and 8, which decreases with increasing content of ytterbium was observed. Temperature dependence of thermoelectric power showed n-p transition at 410 and 467 K for x=0 and 2, respectively, and n-type conductivity for x=8, indicating mainly n-type electrical conductivity. A breakdown voltage of 26 V/mm is mainly observed for the I-V characteristics at 400 K and showing a varistor-like behavior.
6
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Ferromagnetic Order in Single-Crystalline (Cd_{x}Al_{y})[Cr_2]Se_{z} Semiconductors

88%
Duda H., Rduch P., Malicka E., Groń T., Kusz J.
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EN
Measurements of the magnetic properties, the electrical conductivity and the Seebeck effect were performed on single crystals (Cd_{x}Al_{y})[Cr_2]Se_{z} between 77 and 300 K. All samples have a ferromagnetic order with the Curie temperature of 130 K and the paramagnetic Curie-Weiss temperature of 155 K. Both these temperatures do not depend significantly on the Al substitution. The electrical conductivity of single crystals CdCr_2Se_4 doped with Al was p-type and showed the change of log σ versus 1/T slope above 150 K. This fact is interpreted as being due to the onset of impurity conduction and structural defects.
7
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High Spin-Low Spin Transitions in Cu_{0.2}Co_{0.76}Cr_{1.83}Se_4 Semiconductor

88%
Maciążek E., Groń T., Pacyna A., Mydlarz T., Krok-Kowalski J.
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EN
Magnetization, ac and dc magnetic susceptibility measured in the zero-field-cooled mode were used to study the high spin-low spin transitions in polycrystalline Cu_{0.2}Co_{0.76}Cr_{1.83}Se_4 semiconductor. The real part component of fundamental susceptibility χ_1' (T) and its second (χ_2) and third (χ_3) harmonics revealed two spectacular peaks at 128 K and at 147 K, confirming the appearance of the spin-crossover phenomenon.
8
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Hopkinson-Like Effect in Single-Crystalline CdCr_2Se_4 and Cd[Cr_{1.89}Ti_{0.08}]Se_4

88%
Malicka E., Groń T., Pacyna A., Duda H., Krok-Kowalski J.
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EN
The static (dc) and dynamic (ac) magnetic measurements of CdCr_2Se_4 and Cd[Cr_{1.89}Ti_{0.08}]Se_4 showed their ferromagnetic properties with a Curie temperature T_{C} ≈ 130 K and revealed on the real component of ac susceptibility curve, the peaks near T_{C} at 200 Oe, 450 Oe and 1 kOe, characteristic for the Hopkinson ones. The meaningful reduction of saturation moment to 4.73 μ_{B}/f.u. for Cd[Cr_{1.89}Ti_{0.08}]Se_4 suggests the diamagnetic configuration of Ti ions, which dilutes the ferromagnetic sublattice of Cr ones and causes reducing of the energy losses visible on the imaginary components of ac susceptibility curve. Close for zero values of higher susceptibility harmonics above T_{C} are pointing out to the lack of the spin fluctuations in the paramagnetic state.
9
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Superparamagnetic-Like Behaviour in RE_2WO_6 Tungstates (Where RE = Nd, Sm, Eu, Gd, Dy, Ho and Er)

88%
Groń T., Tomaszewicz E., Urbanowicz P., Duda H., Mydlarz T.
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EN
The magnetization isotherms were used to study the superparamagnetic-like behaviour in polycrystalline (powder) RE_2WO_6 tungstates (where RE = Nd, Sm, Eu, Gd, Dy, Ho and Er). The magnetization isotherms of the majority tungstates under study revealed both the spontaneous magnetic moments and hysteresis characteristic for the superparamagnetic-like behaviour with blocking temperature T_{B} ≈ 30 K except the Sm_2WO_6 and Eu_2WO_6 compounds.
10
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Electrical and Magnetic Characterization οf ZnCr_{2-x}V_{x}Se_{4} Spinel Semiconductors

88%
Duda H., Malicka E., Groń T., Pacyna A., Kusz J.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
962-963
EN
Single crystals of ZnCr_{2}Se_{4} spinel doped with vanadium were prepared by chemical vapour transport. The chemical compositions of three crystals have been determined by X-ray diffraction. The structure refinement using the SHELXL-93 program system determine the cation distribution in the system as ZnCr_{2-x}V_{x}Se_{4}. For x values equal to 0.03, 0.1 and 0.13 the observed symmetry was cubic, space group Fd3m. Based on the structural data, influence of the V ions on the magnetic and electrical properties has been analyzed.
11
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Influence of Temperature on Critical Fields in Zn_{x}Sb_{y}Cr_{z}Se_{4}

88%
Malicka E., Groń T., Duda H., Pacyna A., Krok-Kowalski J.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
964-966
EN
The electrical and complex ac dynamic magnetic susceptibility measurements were used to study an influence of temperature on critical fields in single-crystalline Zn_{x}Sb_{y}Cr_{z}Se_{4} spinel system with y = 0.11, 0.16 and 0.20. The p-type conduction and a shift both of the Néel temperature T_{N} to lower temperatures and a susceptibility peak at T_{m} in the paramagnetic region - to higher temperatures were established. Below T_{N} the magnetic field dependence of susceptibility, χ_{ac}(H), shows two peaks. First peak at the critical field H_{c1} slightly decreases with temperature and remains almost constant as Sb content increases. Second peak at the critical field H_{c2} drops rapidly with temperature and remains almost unchanged as Sb content increases. At T_{N} both critical fields disappear.
12
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Coherent Ferromagnetic Precipitate and Anomalies in the Heat Conduction and Thermopower of Mn_{2-x}Cr_{x}Sb Single Crystals

88%
Kattwinkel A., Kraus E., Kleeberg C., Groń T., Bärner K.
Acta Physica Polonica A
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1998
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vol. 93
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issue 5-6
745-762
EN
The heat diffusivity D, the electrical resistivity ρ and the thermoelectric power S of tetragonal Mn_{2-x}Cr_{x}Sb single crystals with 0.02 < x < 0.12 have been measured in the temperature range of 90 K < T < 350 K and along different crystal axes. The heat conductivity κ and σ = 1/ρ are anisotropic along the crystal axes a, c with a ratio of 2:1. κ(T) , ρ(T) and S(T) show anomalies at the spin reorientation temperature T_{Rm} of the matrix (M) Mn_{2-x}Cr_{x}Sb, but also at that of the coherent ferromagnetic precipitate (P) Mn_{1.037}Cr_{0.11}Sb, T_{R}_{p} which is assigned to variations in the spin dependent scattering at the M /P interfaces via changes in the relative orientation of the magnetization vectors of matrix and precipitate (spin valve effect).
13
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Electric Relaxation in Nb₆VSb₃O₂₅-Ceramics

88%
Groń T., Filipek E., Piz M., Kukuła Z., Pawlus S.
Acta Physica Polonica A
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2016
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vol. 129
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issue 3
355-358
EN
Broadband dielectric spectroscopy measurements of Nb₆VSb₃O₂₅ showed that in both the real (ε') and imaginary (ε'') components of permittivity there is visible relaxation process strongly obscured by dc conductivity. Application of the electric modulus representation of the data enables to study temperature evolution of this relaxation together with conductivity relaxation. It was showed that the activation energies for both processes are close. Low-frequency loss tangent increases strongly with temperature, suggesting that in the compound under study additional energy losses are associated with the conduction of electric current, as determined by the Joule-Lenz law.
14
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Electrical and Magnetic Studies of Zn_{x}Mn_{y}Cr_{z}Se_{4} p-Type Semiconductors

76%
Jendrzejewska I., Groń T., Duda H., Zajdel P., Pacyna A., Maciążek E.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
913-915
EN
The structural, electrical and magnetic investigations carried out on the Zn_{x}Mn_{y}Cr_{z}Se_{4} polycrystals with y = 0.19, 0.29 and 0.38 revealed the spinel structure with the Mn ions occupying tetrahedral sites, p-type conduction with polaronic transport at high temperatures and antiferromagnetic order with a Néel temperature of 20 K and a Curie-Weiss temperature of 103 K. With increasing Mn content in a sample both the effective magnetic moment and the re-entrant temperature increase while the first and second critical fields connected with a metamagnetic transition and the breakdown of the conical spin arrangement decrease, respectively. These results are interpreted in terms of giant cubic anisotropy as well as an effect of Mn impurities on the screw structure of ZnCr_{2}Se_{4}.
15
Content available remote

Electrical Properties of Sr₂InV₃O₁₁

76%
Groń T., Filipek E., Pacześna A., Urbanowicz P., Sawicki B., Duda H.
Acta Physica Polonica A
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2016
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vol. 130
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issue 5
1239-1241
EN
The electrical conductivity σ (T) and thermoelectric power S(T) measurements of Sr₂InV₃O₁₁ showed the insulating state and the change of sign of thermopower from p to n at T_{n-p}=400 K. The I-V characteristics provided the evidence of symmetrical and non-linear behaviour typical of strong emission of charge carriers induced by temperature and voltage. Relative dielectric permittivity ε_{r} as well as loss tangent (tan δ) strongly depend both on the temperature in the range of 295-400 K and the frequency in the range of 5×10² to 1×10⁶ Hz, showing the broad maximum at 320 K. These effects are considered as a relaxation process like in the Maxwell-Wagner or Jonscher model as well as the conduction of electric current, as determined by the Joule-Lenz law.
16
Content available remote

Correlation between the Band-Gap Energy and the Electrical Conductivity in MPr₂W₂O₁₀ Tungstates (Where M = Cd, Co, Mn)

76%
Sawicki B., Tomaszewicz E., Piątkowska M., Groń T., Duda H., Górny K.
Acta Physica Polonica A
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2016
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vol. 129
|
issue 1a
A-94-A-96
EN
The values of the direct allowed energy gap determined from the UV-vis-NIR measurements and Kubelka-Munk transformation decrease from 3.38 via 2.70 to 2.42 eV for MPr₂W₂O₁₀ in the sequence M = Cd, Co, Mn, while the values of the activation energy increase from 0.11 via 0.44 to 0.47 eV in the same sequence. In other words, the higher the activation energy, the smaller the energy gap. Because the energy gap is typical for insulators, so electron transport phenomena are considered under the Poole-Frenkel effect and small-polaron mechanism.
17
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Spin Crossover in Cu_{x}Co_{y}Cr_{z}Se_4 Semiconductors

76%
Maciążek E., Groń T., Pacyna A., Mydlarz T., Zawisza B., Krok-Kowalski J.
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EN
Magnetization and magnetic susceptibility measured in the zero-field-cooled mode were used to study the spin crossover transition in polycrystalline Cu_{x}Co_{y}Cr_{z}Se_4 compounds. With increasing Co content a transition from ferromagnetic order via ferrimagnetic one to antiferromagnetic-like behaviour was observed. This transition is accompanied with a lowering symmetry from cubic to monoclinic and for the latter the spin crossover phenomenon occurs. These results are considered in a framework of the ligand-field split and the spin-orbit coupling.
18
Content available remote

Mictomagnetic Order in Cd_{0.87}Cr_{1.93}V_{0.06}Se_4 Semiconductor

76%
Groń T., Malicka E., Zawisza B., Duda H., Krok-Kowalski J., Pacyna A.
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EN
The complex ac dynamic magnetic susceptibility was used to study the mictomagnetic-like behavior in polycrystalline Cd_{0.87}Cr_{1.93}V_{0.06}Se_4 spinel. The temperature dependences of the zero field in-phase (real part) and out-of-phase (imaginary part) components of fundamental susceptibility measured at the oscillating field H_{ac} = 0.5 Oe and at the constant frequency of 125 Hz are characteristic for the mictomagnetic order. These results well correlate with the anomalies in the second and third harmonics of the ac susceptibility indicating the cluster glass.
19
Content available remote

Magnetic Coupling in CuCr_2X_4 (X = S, Se) Spinel Compounds Obtained via Substitution of the Chromium Ions by Nonmagnetic Sb or Al Ions

76%
Krok-Kowalski J., Malicka E., Władarz G., Groń T., Pawełczyk M., Heimann J., Pacyna A.
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EN
Taking into account both the dc magnetic susceptibility and the magnetization measurements as well as the high-temperature expansion of the magnetic susceptibility procedure the hopping integrals and superexchange integrals for the first and second coordination sphere were evaluated. The two hopping integrals are positive and many times greater than the superexchange ones. The obtained results testify to that in the stoichiometric compounds under study the double-exchange magnetic interaction is the main mechanism responsible for very strong, ferromagnetic coupling. Using the total hopping integral B the bandwidth of mixed valence band of chromium ions was determined.
20
Content available remote

Specific Heat and Magnetic Properties of Single-Crystalline (Zn_{0.925}In_{0.054})[Cr_{1.84}In_{0.152}]Se_4 Semiconductor

76%
Malicka E., Groń T., Pacyna A., Ślebarski A., Goraus J., Gągor A., Mydlarz T.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1108-1110
EN
An antiferromagnetic order with a Néel temperature T_{N} = 17.5 K, a strong ferromagnetic exchange evidenced by a positive Curie-Weiss temperature θ_{CW} = 77.3 K, the fuzzy peaks in the real component of susceptibility χ'(T) and the disappearance of the second critical field were established. The curvature of specific heat C(T) and C(T)/T in surrounding of T_{N} indicated a broad peak, characteristic for the system with inhomogeneous magnetic state (spin-glass-like phase). The calculated magnetic entropy showed the value of S(T) ≈ 1 J/(mol K) which is extremely small; i.e., much lower than the magnetic contribution Rln(2S + 1) = 11.52 J/(mol K) calculated for the spin 3/2.
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