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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

100%
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.
2
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Influence of Cu, Ga and Au Dopants and Technology Conditions on the Magnetic Interactions in HgCr_2Se_4 Single Crystals

100%
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.
3
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Critical Behaviour of the Mean-Field Ferromagnet Cu_{1.02}[Cr_{1.77}Ti_{0.24}]Se_4

100%
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.
4
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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

84%
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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