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This article reports exchange bias (EB) and memory effect in nanocrystalline CoCr2O4 with a detailed understanding of the origin of the observed effect. In order to investigate the EB effect in nanocrystalline CoCr2O4, two samples are synthesized with particle sizes 12 and 7 nm via sol-gel route (the second one is embedded in amorphous silica host). For both the samples, despite usual core-shell interaction or ‘surface’ domination, conventional EB effect is observed where the EB field sharply decreases with temperature and vanishes over the spiral ordering temperature (TS) of the samples. A bulk sample of the same composition, with particle size greater than 150 nm, reproducing similar characteristics, rules out the origin of EB due to surface effect. Results indicate that the exchange bias is due to inherent magnetic inhomogeneity: interaction between spiral spin order and collinear ferrimagnetic order below TS. The ac-susceptibility measurement points towards absence of surface glassiness in the sample with 12 nm particle size. However, the sample with particle size 7 nm reveals the characteristics of superspin-glass (SSG), confirmed by magnetic memory effects both in time (t) and temperature (T) dependent magnetization protocols.

The present study has examined the thermodynamics of MgAl2O4 and MgO formations in Al–Mg alloy/quartz (>99% crystalline silica) through differential thermal analysis (DTA). The formation of MgAl2O4 and MgO is detected as exothermic peaks in the heat flow curve and the reaction is confirmed by the Si dissolution peaks observed during the reheating of samples and SEM analysis of the reacted sample. The presence of MgAl2O4 and MgO is confirmed in the XRD analysis of the reacted sample. The study has enabled the production of nano sized MgAl2O4 and MgO crystals at the interface of Al–Mg alloy and quartz. The reaction between them is found to be influenced by the oxidation of Mg, which is reduced by increasing heating rates.

Equal channel angular pressing (ECAP) of in situ Al-5 wt% TiB2 composite was successfully carried out at room temperature up to four passes. Large particle free zones of about 50-100 ?m size present in as cast condition have been reduced to 20-30 ?m by ECA pressing. The initially clustered distribution of TiB2 has become homogeneous after four ECAP passes. A significant grain refinement down to ?500 nm has been achieved by ECA pressing but the average particulates size remains unchanged at 0.5-0.6 ?m. � 2007 Elsevier B.V. All rights reserved.

Aluminium matrix composites reinforced with molybdenum aluminide nanoparticles were synthesized by ball milling and reactive sintering of the mixture of aluminium and 10 wt% hydrated molybdenum oxide powders. Sintering the as milled powder in air below 750 °C produced MoAl12 intermetallic compound nanoparticles, at 750 °C produced a mixture of MoAl5 and MoAl4 nanoparticles and at 800 °C under Argon atmosphere produced predominantly MoAl4 intermetallic nano-particles in the Al matrix. The powder compacts sintered in air below 750 °C produced MoAl12 whereas at 750 °C or above formed the Al matrix composite reinforced with the MoAl5 nanoparticles. These nanoparticles become agglomerated to take up some irregular shaped flakes in the metal matrix. The reaction between Al and hydrated Mo oxide powders was found to be a favorable way to produce predominantly a particular Mo–Al intermetallic compound at a particular temperature. The Al2O3 particles formed as another reaction product, in all the above reactions, remain distributed in these composites. The composites thus formed were characterized by SEM-EDS, DTA, XRD and TEM analysis.

27Al nuclear magnetic resonance (NMR) studies were performed in CeNiAl4, a fluctuating valence system with Kondo temperature T*≈99 K and showing heavy fermion behavior at low temperature. The temperature dependence of the lineshape and the spin lattice relaxation rate (1/T1) were measured in the range 75–300 K. The effect of Ce-4f electron moment on the lineshape was found to be less pronounced. Moreover, the contribution of the 4f electron spin fluctuation to the Al nuclear spin-lattice relaxation process was also found to be less effective in this temperature range compared to that of the contact interaction of the conduction electrons. This suggests a faster spin fluctuation rate of the Ce-4f electron compared to the NMR time scale.