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Nanosized particles of iron oxide (NPIO) has been applied extensively as contrast medium for magnetic resonance imaging (MRI). Recently, micrometer sized particles of iron oxide (MPIO) has also been demonstrated the feasibility for cell labeling to monitor immune response. In this study, we compared the cellular labeling efficiencies of these two kinds of magnetic particles. The NPIO exhibit stronger saturation magnetization and produce more MRI signal change. On the contrary, MPIO revealed better particle uptake ability than NPIO in incubated cells. Microscopically, both MPIO and NPIO were located in the cytoplasm but not in the cell nucleus. On MRI examination, MPIO labeled cells showed more pronounced signal change compared to NPIO labeled cells. We conclude that MPIO is more efficacious in cell labeling than NPIO. Further development and improvement of MPIO for its magnetization will facilitate its MRI applications on stem cell trafficking, evaluation of transplantation rejection and monitoring immune responses.

AC susceptibility of the Rb3C60 superconductor shows a weak dependence on ac magnetic-field frequency f. The temperature, Tp where χ″ is maximum, rises with increasing frequency and the effect is enhanced as the dc magnetic-field amplitude Hdc is increased. The temperature is found to obey a scaling law (1 − T p /T c ) 3 2 = 1.9 × 10 −4 H dc [ ln (f 0 /f) + 23] + 8 × 10 −5 [ ln (f 0 /f) + 23] , where f0 (≈ 1010 s−1) is a characteristic frequency and Hdc is in tesla. The scaling relationship is in good agreement with the predicted equation based on the model of thermally activated flux motion.

The (Hg0.7Bi0.3)Sr2(Ca1−xPrx)Cu2O6+δ system for 1.0 ≧ x ≧ 0.25 has been prepared. The transition temperature Tc always decreases as the rare-earth substitution parameter x increases. We observed the maximal Tc around x = 0.25 with 91 K. From the viewpoint of doping the ionic size and analytic results of the Pr valence in the x = 1.0 sample, we think that Pr exhibits the trivalent state in this system. No anomalous rare-earth Pr antiferromagnetic (AFM) ordering was observed in the temperature dependence of the susceptibility down to 5 K for the Ca free sample.

Temperature-dependent magnetization and magnetic-hysteresis curves for the zero-field cooled and the field-cooled processes of Rb 3 C 60 superconducting fullerene with T c of 30.5±0.1 K were measured between 5 and 30 K in magnetic fields up to 1 T. Small field-cooled diamagnetism and flux jumps were observed at low temperatures and in low fields. Both results strongly suggest the existence of a rather large pinning strength in our sample. This suggestion is further confirmed by the field-cooled hysteresis curve and high critical current densities, J c ( H , T ), at low temperatures. Based on the major hysteresis loops and the Bean critical-state model, the J c at T = 5 K are 2.1 × 10 6 A/cm 2 for H = 0 T and 5.2 × 10 5 A/cm 2 for H = 0.9 T. These J c values are larger than other powdered superconductors with comparable sample sizes, except for YBa 2 Cu 3 O y . For T >10 K, J c versus H agrees well with the expression: J c ( H , T )= k 1 /(1+ H / H 01 ) n . On the other hand, for T J c ( H , T ) may be expressed as J c ( H , T )= k 2 exp(− H / H 02 ). Here k 1 , k 2 , H 01 , H 02 and n are temperature-dependent parameters. The dependence of J c on temperature thus obeys the empirical scaling relation, J c ( H , T )= J c0 ( H )(1− T / T c ) m , where J c0 and m are field-dependent parameters. For 0.4 T H m equals about 2.

We report the magnetic J c ( T ) in K 3 C 60 and Rb 3 C 60 powder samples for temperatures from 5 K to T c . J c near T c was obtained from AC measurements whereas J c at low temperatures was obtained from DC measurements. In the AC measurements, two χ″ peaks were observed on some of the samples. This is attributed to weak links in granular superconductors. The intragranular J c is much larger than the intergranular J c . The J c ( T ) data are fitted by J c ( T ) = J c (0)(1 − T / T c ) γ , with J c (0) and γ as fitting parameters. In the DC measurements on Rb 3 C 60 , J c depends approximately linearly on temperature. Extrapolating the zero-field DC data to 0 K yields J c (0) = 3.1 × 10 6 A/cm 2 . This is a rather large J c for a powdered superconductor, suggesting strong pinning in these materials. Finally, the values of γ for the intergranular and intragranular components are compared with the predictions of theories.

We investigated the crystallographic, transport and magnetic properties of a strongly electron correlated La0.7(Ba1−xPbx)0.3MnO3+δ series with x=0–1.0. All our samples are in a rhombohedral R 3 c structure of lattice parameters a∼0.550 nm and c∼1.338 nm . We found that the addition of the larger Pb ion in La0.7(Ba1−xPbx)0.3MnO3+δ system does not apparently affect on the metal-insulating and magnetic ordering temperatures as well as the magnetoresistance (MR) ratio. However, it reduces the sintered temperature and improves the electric conductivity. The MR ratios are monotonically linear decreasing with temperature from ∼25% at 5 K down to ∼6% at 300 K for all samples. The chemical disorder effect of the Pb2+ substitution does not change the magnetic properties at low temperatures. It can be contributed to exhibiting the constant hole concentration due to the same ratios of [Ba2+]+[Pb2+]/[La3+] and [Mn4+]/[Mn3+] in these Pb doping manganese oxides. The cluster glass behavior was apparently observed, even for the parent sample of x=0.

Hydrogen (H) absorption by YBa 2 Cu 3 O 7− δ (YBCO) was carried out by exposing the superconducting powders to rf-generated H plasma. We find that both the field-cooled (FC) and zero-field-cooled (ZFC) susceptibilities increase after hydrogenation. The largest enhancement is about 24% for the FC susceptibility at 5K.

The high quality Pr(Ba 2−x Sr x )Cu 3 O y (0 ≤ x ≤ 0.6) crystals with isostructural to R Ba 2 Cu 3 O y (R =Y or rare earth) compounds have been successfully prepared using a stoichiometrically melting growth method without flux. The x-ray diffraction patterns and rocking curves showed the well c-axis-oriented single-crystal nature of these specimens. The lattice parameter, degree of orientation, and crystallinity decrease with the substitution of Sr for Ba. No magnetic ordering was apparently observed in the series (x ≤ 0.6) by the all magnetization data between 5 K to 200 K and within ± 1 T. The χ ab −1 ( T ) with the applied field normal to c -axis have been fitted by simple Curie-Weiss law without considering the crystal field effect and shown the effective moments μ eff of 3.537 μ B for x = 0 and 3.572 μ B for x = 0.2, which is closely the Curie-Weiss moment value of free ion Pr 3+ .

Superconducting Bi-Pb-Ca-Sr-Cu-O oxides have been produced by the rapid thermal melt quenching method. The T c (ϱ mid· ) and T co (ϱ=0) of the as-melted glass sample sintered at 855°C for 24 hours in air were 110 K and 105 K, respectively. The specimen has a large diamagnetic shielding effect and high intragrain critical current density [J c (5K) ≈ 10 7 A/cm 2 at low field] compared with the conventional ceramic-sintered materials. The de Almeida-Thouless phase line (irreversibility line) H∗(T) is obtained by hysteresis curves.

(Tl0.5Pb0.5)Ca2Sr2Cu3Oy compound with Tco = 113 K has been achieved. The intragranular critical current density Jc at Ha = 1 T is estimated to be about 6 × 106 A/cm2 at 5 K and has a logarithmic temperature dependence below 40 K. An anomalous dimpling behavior occurs near the origin of the loop for powder sample. This Jc decreases slightly with magnetic field at low temperature and reaches a stable value at high field. The flux pinning centers may be considered as coming from the grain boundaries by the observation of the strong shielding effect and large hysteresis curves in bulk specimen compared with those in powder specimen.