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Substitution of both Co and Mo at Ru-site in RuSr2Eu1.5Ce0.5Cu2O10-δ system takes place iso-structurally in tetragonal structure (space group I4/mmm) with full solubility. The resistance versus temperature (R versus T) behavior of the pristine sample confirmed superconductivity $(T^{R=0}_c)$ around 25 K. The DC magnetization data (M versus T) for the same sample revealed magnetic transition (Tmag) at 140 K followed by superconducting transition $(T^{\rm dia}_c)$ at 32 K. With progressive Co substitution at Ru-site both $T^{R=0}_c$ and $(T^{\rm dia}_c)$ decrease monotonically and superconductivity is not observed for x ≥ 0.10 (10 at%). The magnetic behavior of materials with Co up to x = 0.2 preserves the magnetic structure of the parent RuSr2Eu1.5Ce0.5Cu2O10-δ compound. For 0.8 ≥ x ≥ 0.2 a clear antiferromagnetic transition at TN=31 K is observed regardless of Co content. In the case of Mo-doped ruthenocuprates Ru1-xMoxSr2Eu1.5Ce0.5Cu2O10-δ, it has been found that the magnetic transition temperature decreases with x. The samples of x = 0.8 and 1.0 are found to have no magnetic or superconducting effects. The values of the superconducting transition temperature obtained from the resistivity versus temperature data increase by 4.5 and 7.0 K for x = 0.2 and 0.4 respectively, and then decrease by 17 K for x = 0.6. The observed variation of Tc with x in case of Mo has been explained in terms of a theory which combines the effects of weakening magnetic behavior and reducing carrier concentration in a phenomenological manner. [ABSTRACT FROM AUTHOR]

A dense phase of a postlayered perovskite Sr3Co2O6 was created by a high-pressure and high-temperature synthetic route and quenched to ambient conditions. The structure of Sr3Co2O6 was determined by synchrotron x-ray powder diffraction. Sr3Co2O6 crystallizes in a K4CdCl6-type structure (an infinite chain-type structure), which is 6% denser than the known isocompositional layered perovskite Sr3Co2O7-δ (δ ∼ 1). The K4CdCl6-type Sr3Co2O6 shows complex magnetic behavior, reflecting its spin-chain nature, as do the analog oxides Ca3Co2O6 and Ca3CoRhO6, whose microscopic magnetic origin is still highly debated. [ABSTRACT FROM AUTHOR]

Abstract: We report synthesis and magnetization of MSr2Y1.5Ce0.5Cu2O10 (M/Y-1222) compounds with M = Ru, Mn and Cr by HPHT. They are synthesized at high-pressure of 6 GPa in optimized temperatures of up to 1450 °C, for Ru, Mn and 1550 °C in the case of Cr based Y/1222, for a time duration of three hours for all the samples. All the samples crystallized with tetragonal structure in I4/mmm space group. Few minor impurities are also seen in the case of Mn,Cr/Y-1222 samples. DC magnetic susceptibility measurements exhibited ferromagnetic like transition for all the three compounds at low temperatures. At 5 K, the magnetization M(H) experiments showed clear ferromagnetic like hysteresis loops for Ru and Mn samples with sizeable returning moment (M r) and coercive field (H c). In the case of Cr/Y-1222 system though, ferromagnetism is visible below around 45 K in susceptibility measurements, the characteristic M r and H c are not seen. To the best of our knowledge the Mn,Cr/Y-1222 phases are synthesized for the first time and the quality of our earlier reported Ru/Y-1222 is improved. [Copyright &y& Elsevier]

Abstract: The highly iron-doping to the rutile TiO2 nano-crystals up to Fe/Ti=0.2 (Ti0.833Fe0.167O2−δ ) was investigated by magnetic and high-pressure annealing study. The magnetic data clearly confirmed the substitution and absence of ferromagnetic order. Instead, presence of anti-ferromagnetic interactions was detected. The high-pressure annealed pellets were revealed highly electrically insulating, reflecting electrical nature of the doped crystals. The result provides a great contrast to what was observed for the thin film form of the doped ferromagnetic TiO2. [Copyright &y& Elsevier]

RuY1.5Ce0.5Sr2Cu2O10, is not superconducting (SC) and orders magnetically at TM=152 K. The Ru moment at 5 K is 0.75μB. Ferromagnetic hysteresis loops are observed below Tirr=100 K. At 100 K, the remanent magnetization (Mrem) and the coercive field (HC) become zero. Surprisingly, at Tirr a reappearance of antiferromagnetic (AFM) hysteresis loops are observed with a peak at 120 K for both Mrem and HC. The paramagnetic constants are: Peff=2.06μB (greater than the 1.73μB expected for low spin Ru5+) and θ=136 K which agrees well with TM. Substitution of Zn (2.5% atm.) for Cu in RuEu1.5Ce0.5 Sr2Cu2O10 (TC=38 K), suppresses TC but does not affect the magnetic features such as: TM and Tirr, Mrem and HC. This indicates that both SC and magnetic states are practically decoupled.We argue that the magnetic structure of this system becomes (i) AFM ordered at TM. (ii) Due to the tilting of the RuO6 octahedra away from the crystallographic c-axis, at Tirr, weak-ferromagnetic (W-FM) order is induced by the canting of the Ru moments. (iii) At TC (TM/TC∼4), the specific materials (M=Eu, Gd) become SC. Below TC, both SC and W-FM states coexist. [Copyright &y& Elsevier]

The magnetic behavior of polycrystalline samples of the magneto-superconductors RuSr2Ln1.5Ce0.5Cu2O10-δ (LnRu-1222, Ln=Y, Ho and Dy) and RuSr2YCu2O8-δ (YRu-1212) is analyzed and compared. Clear evidences for the occurrence of a spin glass phase on all LnRu-1222 samples are provided by ac susceptibility (χac) and dc magnetization measurements. A frequency-dependent peak in χac vs. T measurements, at low magnetic field, is observed. The strong suppression of this peak in the presence of magnetic fields as low as 500 Oe, as well as the results of thermoremanent magnetization (TRM) and isothermal remanent magnetization (IRM) measurements, suggest a spin glass behavior. Interestingly, the same measurements on the YRu-1212 sample show no indication of glassy behavior, contrasting with the results for LnRu-1222. We suggest that frustration of the Ru magnetic moments due to the presence of oxygen vacancies would be favored only in the LnRu-1222 compounds, thus causing the glassy behavior. This idea is supported by the observation of large oxygen deficiency that affects the RuO2 planes in Ru-1222, but does not occur in Ru-1212. [Copyright &y& Elsevier]

A Tb-123 phase with the composition, TbSr2Cu2.7Mo0.3O7+δ, has been synthesized in single-phase form by the solid-state reaction route. Its phase purity has been confirmed from neutron powder diffraction studies. The as-synthesized Tb-123 sample does not show superconductivity down to 5 K. On the other hand, an unusually high antiferromagnetic ordering temperature (TN) of around 7 K is seen for the Tb moments. After 120-atm-O2 post-annealing, bulk superconductivity is achieved in this compound with a superconducting transition temperature (Tc) of about 30 K, without any significant effect on TN. To achieve higher oxygen content and higher Tc, the as-synthesized sample was subjected to high-pressure oxygenation, carried out in a closed cell, at 5 GPa and 400 °C in the presence of AgO as an excess-oxygen source. This sample exhibited superconductivity onset at around 80 K with a Meissner fraction larger than 10% at 5 K. Our observation of superconductivity at 80 K is the highest Tc to-date for the Tb-123 type compounds. [Copyright &y& Elsevier]

Abstract: We performed Co nuclear quadrupole resonance (NQR) measurements on bilayered hydrate cobaltate . The sample we used demonstrates a magnetic transition at , which is observed from susceptibility, nuclear spin-lattice relaxation rate, and NQR spectrum measurements. We observed inhomogeneous broadening of the NQR spectrum below . In order to interpret the internal field distribution, we numerically solved a nuclear-spin Hamiltonian including the nuclear quadrupole interaction and the Zeeman interaction, and estimated the internal fields from the observed Co-NQR spectrum. It is considered that the internal fields possess weak modulation. The obtained internal-field distribution suggests the occurrence of the spin-density-wave ordering. [Copyright &y& Elsevier]

Abstract: Magnetic properties of the calcium ferrite-type are reported. The static susceptibility data reveal a cusp at , suggesting a magnetic glassy transition. Although the crystal structure is essentially different from that of the spinel , the compound shows a similarity of the frustrated magnetism of the spinel. The probable magnetic frustration of the calcium ferrite-type compound might be due to a freezing of geometrically frustrated Mn magnetic moments in a triangular-like alignment. [Copyright &y& Elsevier]

Abstract: The three first members of the Cr-12s2 (s =1,2,3) homologous series, i.e. CrSr2YCu2O8 (Cr-1212), CrSr2(Y1.5Ce0.5)Cu2O10 (Cr-1222) and CrSr2(Y1Ce2)Cu2O12(Cr-1232) are synthesized by high pressure high temperature (HPHT) 6GPa and 1550°C process. Though the Cr-1212 and Cr-1232 could not be formed in single phase with full Cr, the Cr-1222 is achieved in pure phase with space group I4/mmm. These compounds belong to the multi-layered copper oxides series that differ from each other only in terms of the (Ce,Y)-[O2-(Ce,Y)] s−1 layer blocks between two identical CuO2 planes with s =1, 2 and 3. At 5K, the magnetization M(H) experiments showed some ferromagnetic like hysteresis loops though the characteristic M r and H c were not seen clearly. None of the studied compounds exhibited superconductivity down to 5K. [Copyright &y& Elsevier]