Papers by Author: Tadeusz Mydlarz

Abstract: Magnetic susceptibility measurements showed both a weak response to magnetic field and a lack of the Curie-Weiss region for CuEu₂W₂O₁₀ and Cu₃Eu₂W₄O₁₈ tungstates characteristic for the multiplet widths comparable to thermal energy. Magnetization measurements displayed the linear temperature dependence with the lower magnetic moment for Cu₃Eu₂W₄O₁₈ in comparison with CuEu₂W₂O₁₀, indicating that the effect of the electric charges associated with the surrounding ligands can change the multiplet width of individual states. It is affecting the electrical properties of examined tungstates which reveal the insulating state and low relative permittivity εr ~ 29 in case of CuEu₂W₂O₁₀ and the thermally activated p-type electrical conduction for Cu₃Eu₂W₄O₁₈ with the activation energy of 1.11 eV and the large value of εr ~ 217 above the room temperature.

Abstract: Magnetic susceptibility measurements revealed a disordered state of magnetic moments above 4.2 K for all compounds under study, and a weak response to the magnetic field and the temperature for Sm₂W₂O₉ and Eu₂W₂O₉ tungstates. The temperature independent component of magnetic susceptibility has a positive value for RE₂W₂O₉ (RE = Pr, Nd and Gd) indicating a domination of van Vleck contribution. Only for Gd₂W₂O₉ the magnetization is a universal function of µ0H/T, characteristic for the superparamagnetism.

Abstract: A high spin (HS) – low spin (LS) transition has been discovered in the Co[Cr0.5Ga1.5]S4 spinel, where the Co ions occupy tetrahedral sites and the Cr and Ga ions octahedral ones. The latter are diluted by the non-magnetic Ga-ions. Application of magnetic fields revealed ferrimagnetic order with a Curie temperature TC = 126 K, a strong suppression of the magnetic susceptibility () and a slight shift of TC to lower temperatures. A cusp at 15.6 K on the ac (T) curve suggests a spin frustration of the re-entrant type. Characteristic for the HS-LS transition is an inflection point at 150 K on the 1/(T) curve, a lack of the Curie-Weiss region above TC and a small value of the magnetization, 4.76 emu/g at 4.4 K and at a magnetic field of 57.5 kOe.

Abstract: The Co2Sm2W3O14 compound crystallizes in the orthorhombic system, and melts congruently at 1443 K. The magnetic measurements showed that Co2Sm2W3O14 is a paramagnet in the temperature range 4.2-225 K showing both the residual magnetic interactions since the paramagnetic Curie-Weiss temperature   0 and the uncompensated temperature independent contributions of magnetic susceptibility since 0  0. The Brillouin fit of the Landé factor revealed an increase of the orbital contribution to the total magnetic moment of the compound what seems to be responsible for its hard and spontaneous magnetization at low temperatures.

Abstract: Barium hexaferrite (BaFe12O19) powders of particle size of 130 and 180 nm were synthesized by a single microemulsion technique. The influence of the concentration of Ba2+ and Fe3+ metallic ions in the aqueous phase in the microemulsion system on the particle size distribution, crystallinity and magnetic properties of BaFe12O19 was studied. The coercive force and saturation magnetization of the sample obtained at a lower concentration of metallic cations in the aqueous phase were higher than those of the sample obtained at higher concentration.