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This letter describes the magnetoresistance (MR) behavior of the heat-treated polyurethane composites reinforced with iron nanoparticles. The flexible nanocomposites were fabricated by the surface-initiated-polymerization method. The uniformly distributed nanoparticles within the polymer matrix, well characterized by field emission scanning electron microscopy, favor a continuous carbon matrix formation, rendering the transition from insulating to conductive composites. The coercive forces reflect strong particle loading and matrix dependent magnetic properties. By simply annealing in a reducing environment, the obtained nanocomposites possess a MR of 7.3 % at room temperature and 14 % at 130 K occurring at a field of 90 kOe.

The magnetic and electromagnetic wave absorption behavior of a flexible iron-nanoparticle reinforced polyurethane nanocomposite is reported. Surface-initiated-polymerization ͑SIP͒ method was utilized to fabricate high-quality nanocomposites with uniform particle distribution and tunable particle loading ͑up to 65 wt %͒. The enhancement of coercive force is observed when the nanoparticles are embedded into the polymer matrix. Electromagnetic wave absorption performance at a discrete frequency as studied by metal-backed reflection loss indicates that the SIP nanocomposites can save the weight up to 50% compared to the composite counterpart with micron-size particles.

On the incorporation of Mg and the role of oxygen, silicon, and hydrogen in GaN prepared by reactive molecular beam epitaxy

Single crystals of Ln 2 MGa 12 (Ln ) La, Ce; M ) Ni, Cu) have been synthesized using Ga flux and their structures determined by single-crystal X-ray diffraction. The Ln 2 MGa 12 (Ln ) La, Ce; M ) Ni, Cu), which is isostructural to Ce 2 PdGa 12 , crystallizes in the tetragonal P4/nbm (No. 125, origin choice 2) space group, with Z ) 2 and lattice parameters a ≈ 6.1 Å and c ≈ 15.3 Å. Ce 2 NiGa 12 orders antiferromagnetically at 10 K and specific heat measurements suggest it is a moderate heavy-fermion system with γ ≈ 191 mJ mol -1 K -2 . Magnetic susceptibility data show paramagnetic behavior down to 2 K for Ce 2 CuGa 12 , whereas specific heat data suggest a magnetic transition below 1.8 K, with a moderately enhanced γ-value of 69 mJ mol -1 K -2 . Metallic behavior is observed below 300 K for each compound. A large positive and nonsaturating magnetoresistance up to 216% at a field (µ 0 H) of 9 T is also observed for La 2 NiGa 12 . We present the crystal structures and physical properties of the Ln 2 MGa 12 (Ln ) La, Ce; M ) Ni, Cu) series.