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1
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High Spin-Low Spin Transitions in Cu_{0.2}Co_{0.76}Cr_{1.83}Se_4 Semiconductor

100%
Maciążek E., Groń T., Pacyna A., Mydlarz T., Krok-Kowalski J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 3
687-689
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.
2
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Hopkinson-Like Effect in Single-Crystalline CdCr_2Se_4 and Cd[Cr_{1.89}Ti_{0.08}]Se_4

100%
Malicka E., Groń T., Pacyna A., Duda H., Krok-Kowalski J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 3
690-693
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.
3
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Influence of Temperature on Critical Fields in Zn_{x}Sb_{y}Cr_{z}Se_{4}

100%
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.
4
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Electrical and Magnetic Studies of the Cd_{x}Cr_{y}V_{z}Se_{4} Spinels

86%
Groń T., Duda H., Malicka E., Zawisza B., Krok-Kowalski J., Pacyna A.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
969-970
EN
The electrical and magnetic investigations carried out on the polycrystalline spinels with the general chemical formula Cd_{x}Cr_{y}V_{z}Se_{4} (where z = 0.06, 0.12, 0.24, and 0.31) revealed semiconducting and ferromagnetic properties with a Curie temperature of 127.5 K. A step-like structure of the electrical conductivity, σ(T), was observed for the polycrystal containing 6% V ions in the octahedral sites while the remaining samples showed a typical Arrhenius behaviour of σ(T). These effects are interpreted in terms of ferromagnetic spin clusters which finally dissolve on going towards the paramagnetic limit including non-stoichiometry.
5
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Effect of Cation Substitution on Critical Fields in the n-type Zn_{x}Sn_{y}Cr_{z}Se_{4} Spinel Semiconductors

86%
Groń T., Jendrzejewska I., Maciążek E., Pacyna A., Duda H., Zajdel P., Krok-Kowalski J.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
971-974
EN
The ac dynamic magnetic susceptibility was used to study a cation substitution on critical fields in polycrystalline (Zn_{0.87}Sn_{0.048})Cr_{2.02}Se_{4} and Zn_{0.93}[Cr_{1.95}Sn_{0.05}]Se_{4} spinels with tetra- and octahedral coordination of Sn ions, respectively. An increasing static magnetic field shifts the Néel temperature T_{N} to lower temperatures while a susceptibility peak at T_{m} in the paramagnetic region - to higher temperatures. Below T_{N} the magnetic field dependence of susceptibility, χ_{ac}(H), shows two peaks at critical fields H_{c1} and H_{c2}. The values of H_{c1} decrease slightly with temperature while the values of H_{c2} decrease strongly with temperature, especially for spinel with octahedral coordination of Sn ions, suggesting a weakness of the ferromagnetic component.
6
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Spin Crossover in Cu_{x}Co_{y}Cr_{z}Se_4 Semiconductors

86%
Maciążek E., Groń T., Pacyna A., Mydlarz T., Zawisza B., Krok-Kowalski J.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
711-713
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.
7
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Mictomagnetic Order in Cd_{0.87}Cr_{1.93}V_{0.06}Se_4 Semiconductor

86%
Groń T., Malicka E., Zawisza B., Duda H., Krok-Kowalski J., Pacyna A.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
714-716
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.
8
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Magnetic Coupling in CuCr_2X_4 (X = S, Se) Spinel Compounds Obtained via Substitution of the Chromium Ions by Nonmagnetic Sb or Al Ions

86%
Krok-Kowalski J., Malicka E., Władarz G., Groń T., Pawełczyk M., Heimann J., Pacyna A.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
705-707
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.
9
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Influence of Cu, Ga and Au Dopants and Technology Conditions on the Magnetic Interactions in HgCr_2Se_4 Single Crystals

86%
Krok-Kowalski J., Władarz G., Groń T., Duda H., Pacyna A., Nikiforov K., Rduch P.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
970-972
EN
For single crystals HgCr_2Se_4 doped by nonmagnetic Cu^{+}, Au^{2+} and Ga^{3+} ions and single crystals of HgCr_2Se_4 matrix growing in different synthesis conditions both the dc and ac magnetic susceptibility as well as the magnetization have been measured. As it follows from the analysis of the obtained results, paradoxically, the dopants strengthen the long range magnetic interactions of the ferromagnetically ordered single crystals under study, evidenced by the higher values of the ordering temperature in comparison with those ones for pure matrix. An influence of the technological processes connected with deficiency and/or excess of Hg on the long range magnetic interactions was not observed.
10
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Critical Behaviour of the Mean-Field Ferromagnet Cu_{1.02}[Cr_{1.77}Ti_{0.24}]Se_4

86%
Krok-Kowalski J., Władarz G., Rduch P., Malicka E., Groń T., Guzik A.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1102-1104
EN
Magnetization, M, and susceptibility, χ, measurements showed both strong lowering of magnetic moment in comparison with CuCr_2Se_4 matrix and zero-field-cooling-field-cooling susceptibility splitting characteristic for the spin-glass behaviour. Isothermal magnetization curves, M(H), easy saturate and large values both of the Curie T_{C}=253 K and Curie-Weiss θ=283.5 K temperatures indicate the ferromagnetic order which coexists with the spin-glass state. The critical behaviour investigated around the paramagnetic-ferromagnetic phase transition revealed that the values of critical exponents are close to those predicted by the mean field model for long-range magnetic interactions.
11
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Influence of Substitution of the Chromium Ions by the Nonmagnetic Sb and Al Ions on the Magnetization Processes in CuCr_{2}X_{4} ( rm X = S, Se) Spinels

73%
Malicka E., Krok-Kowalski J., Warczewski J., Groń T., Duda H., Mydlarz T., Pawełczyk M., Pacyna A., Rduch P., Władarz G.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
967-968
EN
Both the dc and ac magnetic susceptibilities as well as magnetization measurements were used to study the influence of the dilution of the magnetic chromium subarray by nonmagnetic antimony and aluminium ions on the magnetization processes for four spinel families under investigation. Substitution of the chromium ions by the nonmagnetic Sb and Al ions in the compounds under study leads to the very hard magnetization in the case of the compounds with Sb and very easy magnetization in the compounds with Al. This effect is connected with the electronic configurations of the Sb and Al ions as well as with ionic radii of these cations.
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