Time filter

Source Type

Zayachuk D.M.,Lviv Polytechnic | Mikityuk V.I.,Yuriy Fedkovych Chernivtsy National University | Shlemkevych V.V.,Yuriy Fedkovych Chernivtsy National University | Kaczorowski D.,Institute of Low Temperature And Structure Research | Ilyina O.S.,Lviv Polytechnic
Physica C: Superconductivity and its Applications | Year: 2012

We present evidence of superconductivity of the surface layers of PbTe crystals grown from melt and doped with Eu during growth. We have studied two different type of the powder samples made out of the surface layer and from bulk of the PbTe:Eu ingots. The magnetization in the range of magnetic field 0-5 T and the magnetic susceptibility (MS) in the temperature range 1.7-400 K were investigated. At low temperatures, a strong diamagnetism of the surface layers of the PbTe:Eu ingot is observed whereas at high temperatures a transition to strong paramagnetism takes place. This effect is attributed to the transition of the PbTe:Eu surface layers to state of superconductivity at low temperature. The superconductivity of the doped surface layers is explained by formation of the Pb-based inclusions within the ingot surface. © 2012 Elsevier B.V. All rights reserved.


Zayachuk D.M.,Lviv Polytechnic | Mikityuk V.I.,Yuriy Fedkovych Chernivtsy National University | Shlemkevych V.V.,Yuriy Fedkovych Chernivtsy National University | Kaczorowski D.,Institute of Low Temperature And Structure Research
Journal of Crystal Growth | Year: 2012

The magnetic field dependence of magnetization M(B) at the temperature 1.72 K in magnetic fields up to 5 T and the temperature dependence of magnetic susceptibility (M S) χ(T) in the temperature range 1.7400 K of six PbTe:Eu samples with the concentration of Eu impurity of the order of 1×10 191×10 20 cm -3, prepared from the doped crystals grown from the melt by the Bridgman method, have been investigated. It is shown that the dependence of M(B) and χ(T) can be quantitatively explained by the contribution of the single centers of Eu ions, their pairs, and the matrix of the doped crystals using the same set of parameters for each sample. This is true provided we use in our analysis the values of the exchange integrals between Eu ions in EuO normalized with the lattice constant of PbTe, i.e., J 1/k B=0.056 K for the ferromagnetic interaction of the NN (nearest neighbor) pairs and J 2/k B=-0.13 K for the antiferromagnetic interaction of the NNN (next nearest neighbor) pairs, as well as different values of the M S of crystal χ matrix. It is revealed that the probability of the formation of complexes based on the magnetic impurity pairs is higher in the incipient section of a doped ingot, and it decreases towards the ingot end where the single centers of Eu ions become the only centers of the impurity. We conclude that the pairs of Eu 2 ions, which are formed during the growth of the PbTe:Eu ingots from melt by the Bridgman method, are the constituents of the complexes of the magnetic impurities with the background Oxygen impurities in the crystal matrix of the doped lead telluride. It is shown that the formation of the complexes leads to an increase of the M S of crystal matrix χ matrix and can even cause the change of its sign from minus to plus, i.e., it can convert the crystal matrix from the diamagnetic to paramagnetic state. The possible causes of this effect are analyzed. © 2011 Elsevier B.V. All rights reserved.

Loading Yuriy Fedkovych Chernivtsy National University collaborators
Loading Yuriy Fedkovych Chernivtsy National University collaborators