Piotr W. Klamut

Superconductivity and magnetism in the ruthenocuprates

The ruthenocuprates are high temperature superconductors, which have raised a substantial interest due to the simultaneous presence of the transition metal magnetism and superconductivity. The compounds represent a complex and experimentally challenging research arena, with interesting recent experimental developments. The author reviews some key properties of RuSr2RECu2O8, RuSr2RE2−xCexCu2O10−y, and of a few derivative compounds of the ruthenocuprate family.

The magnetic state of 1212-type ruthenocuprate in magnetocaloric and magnetoresistivity measurements of polycrystalline samples of RuSr2Gd1−xCexCu2O8 and Ru1−xSr2GdCu2O8

The magnetic properties of superconducting Ru1−xSr2GdCu2O8 (x = 0, 0.02) and non-superconducting RuSr2Gd1−xCexCu2O8 (x = 0.07, 0.1) were investigated by means of magnetocaloric experiments with complementary magnetoresistivity and ac susceptibility measurements. The isothermal magnetocaloric coefficient MT(B) assumes positive values in a broad range of temperatures (20 K≤T≤231 K) and magnetic fields (0 T≤B≤13 T), i.e. also in the magnetically ordered state (Tm = 132 K for RuSr2GdCu2O8 and Tm = 150 K for RuSr2Gd0.93Ce0.07Cu2O8) which indicates no gain in the systems magnetic entropy with increasing magnetic field. The maximum in the MT(B) dependence was observed for RuSr2GdCu2O8 in the temperature vicinity of Tm, which indicates a ferromagnetic character of the accessed magnetic correlations. No spontaneous ferromagnetic order was revealed as the MT assumes limiting zero values at zero magnetic field for the whole range of investigated temperatures. Temperature dependences of the specific heat reveal the magnetic-field-induced positive temperature shift of the anomaly associated with the magnetic transition in the Ru spin system. The MT(B) dependences and the magnetoresistivity data suggest that the magnetic system may be inhomogeneous.

Domains of existence and physical properties of the 2201- and 2202-type structure phases in the Bi2O3-SrO-CaO-CuO quaternary system

The domains of existence of the 2201- and 2202-type structures in solid solutions of the Bi2O3-SrO-CaO-CuO quaternary system are investigated from the powder X-ray diffraction, density and resistive transition measurements. It is shown that the general formula of Torardi (1988) should not be identified as describing fixed stoichiometry of Bi-based compounds but as a code according to which the unit cells are to be constructed. The authors have also shown that the composition of the investigated phases can vary within some region of homogeneity. The 2201-type structure acts as a matrix for the formulation of new phases by addition of some quantities of calcium and copper, which are known as 80 K and 110 K superconductors. The influence of oxygen on the properties of Bi-based compounds is also evaluated.

Unusual magnetic properties of UGa 3 single crystals

Abstract The magnetic behaviour of single-crystalline UGa 3 has been studied by means of DC- and AC-magnetic susceptibility and thermal conductivity measurements. As many as three pronounced singularities have been found in both, the χ(T) and κ(T) variations. The features at T N = 65K are associated with an antiferromagnetic phase transition while those at T 1 = 40K and T 2 = 8K have an unknown origin. At low temperatures a significant diamagnetic response is observed in χ′(T) accompanied by a rapid rise in χ″(T) . This behaviour of the AC-susceptibility is strongly dependent on the frequency of the alternating magnetic field and on the strength of the external steady magnetic field.

Constitution of Bi2(Sr1-xCax)2Cu2Oy and of Bi8(Sr1-xCax)8Ca4Cu10Oy type solid solutions

Analytical explanation of an unexpected behaviour of sample densities is given. Three different types of construction of the investigated solid solutions have been recognised: normal for Z=constant versus increasing contribution of Sr substituent (X); atom-deficient for Z decreasing with X; atom-overcrowded for Z increasing with X. The mechanism of mutual transformation of the 2201-type matrix to that of the 2212-type is proposed.

EPR study on higher oxygen pressure synthesized compound Pr2−xGdxCuO4

Abstract The electron paramagnetic resonance (EPR) and magnetic susceptibility measurements were performed in Pr 2− x Gd x CuO 4 (x=0.02; 0.05) annealed at the higher oxygen pressures of 15 and 21 bar. This annealing treatment causes a reduction of about 8% in the second order crystalline electric field (CEF) parameter | b 2 0 | at the Gd 3+ site and leads to a drastic broadening of the Gd 3+ resonance lines, which is consistent with spin relaxation processes of Gd 3+ due to the first excited state of Pr 3+ , an increase in the CEF inhomogeneity upon doping and annealing, and an existence of Pr ions in both 3 + and 4 + oxidation states. The exchange coupling constants j Pr−Pr and j Gd−Pr are also estimated.

Commentary on the superconducting and magnetic properties of the ruthenocuprates

Presented in this commentary is a short discussion of the superconducting and magnetic properties of selected compounds of ruthenocuprates, with an emphasis given to the RuSr2GdCu2O8 compound. The ruthenocuprates, which form derivative class in the cuprate family, continue raising interest for there evidenced presence of magnetic ordering in the sublattice of Ru ions, which in polycrystalline samples of RuSr2GdCu2O8 sets at Tm ≈ 132 K, and at low temperatures may become simultaneous with the superconducting phase (Tc,max ≈ 50 K)-all that in the crystal structure derived from well known REBa2Cu3O7 cuprate superconductor. While several here invoked recent results advocate for an intrinsically inhomogeneous nucleation of superconductivity within this structure, the formed superconducting phase carries potential of maintaining substantial anisotropy with then interesting consequence for probing the cuprate characteristic superconductivity in these compounds.PACS Codes: 74.72.-h, 74.25.Ha, 74.81.-g

Low temperature irreversibilities in the magnetothermal behavior of Gd2CuO4

The detailed investigation of the low temperature magnetic properties of Gd2CuO4 reveals the irreversible temperature behavior of the dc magnetization and ac susceptibility that is associated with the presence of magnetic anomalies inbetween TNGd=6.6 K and T1≈20 K. Observed hysteresis is centered around 8 K—the temperature of the sudden drop in the magnetization that corresponds to the temperature of reorientation-type magnetic phase transition in the Cu sublattice. The significant irreversibility has also been found in the temperature range of the magnetic anomaly at T1≈20 K. Following the theoretical model of the low temperature magnetic interactions proposed in Vitebsky et al. [Fiz. Niz. Temp. 20, 25 (1994)], the irreversible behavior around T1 can be qualitatively understood assuming the existence of the magnetic clusters in the form of groups of Gd–Cu–Gd sandwiches. Comparing the results obtained for quenched and slowly cooled samples it can be concluded that the long distance coherence, presumably o...

Influence of hydrogenation on inter‐ and intragranular critical currents in YBa2Cu3O7−δ

The influence of hydrogenation on the inter‐ and intragranular critical current density has been studied using an ac technique. With increasing hydrogen content, intergranular critical current density decreases drastically, whereas pinning inside the grains is increased.

Effect of Sr and H doping on the Magnetic Properties of Sm2CuO4

In order to investigate the possible effects of the changes of charge carrier concentration on the magnetic properties of Sm2CuO4, we measured the ac susceptibility temperature dependences for hole-doped Sm2−xSrxCuO4 (0 ≤ x ≤ 0.1) and HySm1.93Sr0.07CuO4 (0 ≤ y ≤ 0.2) series of compounds. It is shown that Sr substitution builds up the maximum in ϰ′(T) at about 12 K, whereas H dopig suppresses this anomaly. The possible origins of the maximum occurrence are discussed in the context of available data on other T′ type structure compounds. Simultaneously, it is shown that the temperature of AF transition of Sm ions sublattice decreases with samples hydrogenation. It suggests that hydrogen plays a role of electron donor in these compounds.