Materials Science Forum Vol. 700

Abstract: NMR spin shift data of La1:85Sr0:15CuO4, HgBa2CuO4+ at ambient pressure, andof YBa2Cu4O8 at pressure up to 63 kbar are discussed that fail the traditional single-electronicuid picture used for the discussion of NMR data. Instead the results point to a commonexplanation for all three systems in terms of two electronic components. One of them hasa temperature-dependent magnetic susceptibility while the second component, as well as itscoupling to the rst component, are constant above the superconducting transition temperatureTc. All susceptibilities vanish below Tc.

Abstract: We investigate the pinning force anisotropy for BSCCO and YBCO commercial wires at 77 K. The pinning force is measured to 3 T and for all field angles. We show that the magnitude of the pinning force maximum as a function of applied field angle follows known statistical functions. The position of the maximum with field also follows these functions. This is a step towards a Dew-Hughes type scaling covering field, field angle and temperature for HTS wire.

Abstract: Raman measurements were made on polycrystalline Bi2􀀀xPbxSr1:6Ln0:4CuO6􀀀 for Ln=fLa,Nd, Sm, Eug with various x and doping states. Our measurements suggest a signi cant Bicontribution to the 118cm􀀀1 mode but not to the 70cm􀀀1 mode which instead shifts to lowerfrequencies with increasing number of CuO2 layers in the Bi-based family. Shifts in the O(2)Srapical oxygen mode can be attributed to unit cell contraction within experimental error.

Abstract: We study the formation mechanism of nanoparticles in thin films of the superconductor YBa₂Cu₃O_7-δ (YBCO). We form the films by metal-organic deposition (MOD) on buffered, textured metal substrates. Through the addition of Dy or Zr salts to the precursor solution we precipitate (Y,Dy)₂O₃ and BaZrO₃ nanoparticles, uniformly distributed through the film thickness. By quenching samples during the film growth, we show the nanoparticles form in the precursor layer before YBCO growth. The size of the nanoparticles was quantitatively analysed by TEM. We found that Zr doping produces smaller nanoparticles than Dy doping.

Abstract: We report the results from magnetotransport measurements on polycrystalline Sr_2-xLa_xFeMoO₆ samples at magnetic fields of up to 8 T. We observe a normal as well as an anomalous Hall effect. We find that there is a small decrease in the normal Hall coefficient for La doped samples.

Abstract: Ti-rich Mg1ЎxTi1+xO3 samples were synthesized by solid-state reaction. Sampleswere characterized by room temperature x-ray powder di®raction, scanning electron microscopyand energy dispersive spectroscopy of x-rays. Hexagonal lattice parameters a and c increasedwith increasing Ti content. Time-of-Flight-Secondary-Ion-Mass-Spectroscopy (ToF-SIMS, de-tection limit 10Ў6) measurements revealed that no magnetic impurities were present. Sampleswith x = 0:10; 0:12 and 0:32 showed ferromagnetic hysteresis loops. The result demonstratesthat excess Ti at the Mg-O cation layer controls the magnetic properties. This is a technologicaladvantage especially for thin Їlm applications.

Abstract: The effect of manganese doping on the magnetic and structural properties of strontiumtitanate (SrTiO3) was studied. Neutron powder diffraction, x-ray diffraction, magneticmeasurements, scanning electron microscopy and energy dispersive spectroscopy of x-rays wereutilized. Air-sintered Sr(MnxTi1-x)O3 (SMT) with x = 0:02 and x = 0:05 were homogeneoussingle phase orthorhombic (space group Pbnm) perovskite samples. The symmetry was orthorhombicalready at room temperature, and no symmetry change was observed down to 11K. An anomaly in the magnetic susceptibility was observed in x = 0:02 sample at 75 K. Incontrast to earlier reports, no ferromagnetism was observed.

Abstract: We observe a large magneto-resistance in very thin Ba₂FeMoO₆ films of ~-12% at 10K, which is not significantly changed when thin NiFe/Ba₂FeMoO₆ bi-layers are made. This suggests that the magneto-resistance in both cases is dominated by inter-grain tunnelling in the Ba₂FeMoO₆ thin film. There is an anomalous peak in the resistance at ~300K in the bi-layer film that can not be easily explained. However, we know that the temperature where this peak occurs is close to the Ba₂FeMoO₆ Curie temperature.

Abstract: We have fabricated surface magnetic iron nanoclusters using low energy Fe⁺ implantation and electron beam annealing. We find that changing the fluence has a significant effect on the nanocluster growth, structural and magnetic properties. Low fluences lead to small nanoclusters and superparamagnetism, while high fluences result in larger chain-like nanoclusters that have high remnant magnetizations and a significantly reduced saturation field. Our results show that the nanostructure and the magnetic properties can be tuned by varying the Fe⁺ fluence, which means that a reliable method can be used to make surface nanoclusters for a variety of applications (e.g. large magnetoresistance sensors with no hysteresis).