Nano-Al2O3 doped Mg1−xAlxB2 with 0≤x≤6% were synthesized by solid state reaction at 750 °C in Fe tube encapsulation under a vacuum of 10−5 Torr. Resistance measurement shows that the Tc decreases with x and zero resistivity for x = 0 and 6% are obtained at 38 and 35 K, respectively. XRD measurement shows that the lattice parameter and cell volume also decrease monotonically with increasing doping levels. From this we infer that the Al has been substituted in the lattice of MgB2 at Mg sites. Resistivity measurement shows a systematic decrease in Tc with doping which also confirms the substitution of Al. Magnetization studies in the temperature range from 4 to 35 K and in the magnetic field up to 9 T shows a significant increase in the irreversibility field (Hirr), critical current density (Jc) and remanent magnetization (MR) with increasing concentration of the Al2O3 nanoparticle. At low fields we have observed large vortex instabilities (known as a vortex avalanche) associated with all doped samples. The vortex-avalanche effect is reduced with increasing temperature and vanishes near 20 K. The results are discussed in terms of local-vortex instabilities caused by doping of Al2O3 nanoparticles.

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α-Fe2O3 nanoparticles were obtained by a mechanical alloying of micrometer-sized powder at different milling times. Samples were characterized by X-ray powder diffraction, scanning electron microscope (SEM), Mössbauer spectrometry, and vibrating sample magnetometer (VSM). A qualitative and quantitative phase analyses using the Rietveld method have been performed based on the XRD data. The results did not reveal any phase change during the milling. The average particle size decreases with a prolongation of milling times, while the lattice parameters, unit cell volume, and microstrain increase. Mössbauer measurement shows that there are two components, one nanometric and other micrometric. The magnetic hysteresis loops shows that the samples are typical of ferromagnet with superparamagnetic fraction in the material.