Gd5Si2Ge2 exhibits the so-called giant magnetocaloric effect, making it a potential material for next-generation near-room-temperature permanent-magnet-based refrigeration devices. In the as-cast form this material is relatively complicated in terms of its structure and its metallurgy.

Recent reports have suggested that small additions of iron can substantially improve the problems associated with hysteresis losses, so enhancing the material's potential for real-world applications. We have looked at iron substitutions in the range X=0 to X=1 for Gd5Si2-XGe2 to investigate the macrostructures and microstructures of cast and homogenized materials, with particular emphasis on the amount of iron substituting for silicon in the Gd5(SiGe)4 phase and the effect of the substituting iron on the Ge/Si ratio. The larger iron substitutions were found to eliminate the unusual macrostructures, and conventional ingots with smooth surfaces were the result. The iron was also found to dissolve at levels of 1-3% in the Gd5(SiGe)4 phase and encourage the formation of the Gd5(SiGe)3 phase at the expense of the magnetocaloric Gd5(SiGe)4 phase. A substitution of X=1 was found to be sufficient to produce as-cast microstructures consisting almost entirely of the Gd5(SiGe)3 phase.

With a scanning electron microscope (Jeol 840A) and an analytical transmission electron microscope (Jeol 2010 F with a field-emission gun) and an EDXS system from Oxford Instruments (Link Isis 300) we performed a detailed microstructural investigation of the processed materials. Special emphasis was placed on the intergrain regions and an assessment of the amount of Fe substituting in the main magnetocaloric phase.

We experimentally test three existing models of organic magnetoresistance (OMAR) which are all based on carrier spin dynamics. We first prove that hyperfine field originating from the hydrogen nuclei in organic materials is necessary for observing OMAR by studying C60 sandwich devices using several different electrode materials. We show that C60, unlike many other organic semiconductors, does not exhibit any intrinsic OMAR effect. However, we find that as soon as the carriers in C60 are brought in proximity with hydrogen-containing compounds, either in the form of a polymeric electrode, or side-chain substituents, a weak OMAR effect is observed. Next, we perform charge-induced absorption and electroluminescence spectroscopy in a polyfluorene organic magnetoresistive device. Our experiments allow us to measure the singlet exciton, triplet exciton and polaron densities in a live device under an applied magnetic field, and to distinguish between three models of OMAR. These models are based on different spin-dependent interactions, namely exciton formation, triplet exciton-polaron quenching and bipolaron formation. We show that the singlet exciton, triplet exciton and polaron densities and conductivity all increase with increasing magnetic field. Our data are inconsistent with the exciton formation and triplet-exciton polaron quenching models.

We have prepared Nd2Fe14B/Fe3B bulk nanocomposite magnets at the compositions of Nd4Fe77.5B18.5-xMx (M=Si, C) by substitution of other elements M for B. For the sample substituted with 1 at.%Si and sintered at 600 oC, the coercivity exhibits the highest value of 227 kA/m. It has also been found that the grain sizes of the Nd2Fe14B and the Fe3B phases depend on the ramp-up time and the reduction of the grain size leads to an increase of the coercivity. On the other hand, the samples substituted with C exhibit soft magnetic behaviors, which is attributed to the suppression of the precipitation of the Nd2Fe14B hard magnetic phase.

We synthesized Ge and Ge1-xMx (M = Mn, Co, and Fe, x ≤ 0.2) nanowires using thermal vapour transport method. All nanowires consisted of single-crystalline Ge nanocrystals grown uniformly with the [111] direction. High-resolution X-ray diffraction pattern shows no cluster formation for all Ge1-xMx nanowires. The Mn and Fe doping decreases the lattice constant, but not Co doping. X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurement revealed that the Mn2+ and Fe2+ ions preferentially occupy the tetrahedral sites, substituting for Ge. We suggest that the Mn or Fe ions produce dopant-acceptor hybridization with host defects in p-type Ge, but not Co ions. The magnetic moment of Mn2+ ions reaches a maximum for x = ∼ 0.1, which is much larger than that of the Fe2+ ions. The magnetization measurement also confirms the room-temperature ferromagnetism of Mn-doped Ge nanowires, which is maximized at x = ∼ 0.1. We conclude that the Mn ions are most efficiently doped into the Ge nanowires to form a ferromagnetic semiconductor.

Bit patterned media, including media fabricated with a gradient in composition, is being developed as a potential path to higher information storage density. The noise level in such media is significantly impacted by the precision of the ordering of the individual bits and by the narrowness of their size distribution. Block copolymers that phase separate on the appropriate length scale are one method of pattern generation that is receiving considerable attention. For cylinder forming block copolymer phases the ordering and degree of perpendicular alignment is largely determined by the matching of the substrate surface to the block copolymer. If the chemical properties of the substrate surface match the average for the block copolymer, then thin films of the block copolymer align perpendicularly on annealing. Although there are a number of examples where the substrate surface fortuitously matches the block copolymer, in general an orienting layer is necessary to provide the appropriate match. The most popular approach has been to synthesize a random copolymer with the same average composition as the block copolymer. In order to produce suitably thin orienting layers it has been necessary to chemically tether the random copolymer to the substrate. Previously used chemistry has not been suitable for noble metal substrates such as platinum. We have been developing an alternate approach using thiol functional groups which we anticipate will be more suitable for Pt capped substrates.

The immobilization of polyinosinic-polycytidylic acid [poly(IC)] on ã-Fe2O3 maghemite nanoparticles via the phosphor-amidate route using a multifunctional polymer is reported. The dsRNA coupled nanoparticles were used to visualize the Toll-like (TLR3) receptors at the cell surface. The presence of TLR3 was demonstrated independently in the Caki-1 cell line by RT-PCR and immunostaining techniques