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Sol gel auto-combustion was used to create gadolinium doped nickel ferrite nano-particles, which have chemical composition NiFe2-xGdxO4 (x = 0.00, 0.010, 0.15, 0.20 & 0.25). The investigation focused on how the composition of Gd+3 affected the magnetic properties and structural parameters. Magnetic properties were investigated using VSM technique, structural properties were determined using XRD and SEM techniques. XRD graphs verified the establishment of the spinel ferrite phase. With an increase in Gd composition, the crystallite size and lattice parameter increased from 21.0288 to 27.04125 nm and 8.3325 to 8.3367Å, respectively. It was also evident how the composition of Gd+3 affected the estimation of bond-angles and lengths in tetrahedral and octahedral structures. SEM micrographs showed that all of the grains had a small amount of agglomeration and that all of the synthesized compositions were homogenous. The range of 140.5--176.2 nm was found to be the average grain size. Using VSM at 300K, magnetic parameters like coercivity, residual magnetization, and saturation magnetization were computed. Until the composition was 0.20, the saturation magnetization and residual magnetization dropped from 30.28 emu/g to 15.35 emu/g and 5.07 emu/g to 3.65 emu/g, respectively. After that, they increased to 34.40 emu/g and 6.52 emu/g, respectively. Until composition 0.20, coercivity was raised from 154 to 261 Oe; after that, it was lowered to 233 Oe. [ABSTRACT FROM AUTHOR]

Studies on design optimisation of eddy current probe have been carried out for detection of deep sub-surface defects in thick stainless steel plates. The performance of send-receive type air core, ferrite core, ferrite core with outer shielding, and cup-core probes has been analysed and compared using finite element modelling. The model predicted results have indicated that the cup-core probe ensures better sensitivity for detection of deep sub-surface defects. For experimental studies, a high sensitive eddy current instrument with digital lock-in amplifier functionality implemented in LabVIEW software has been developed. Experimental results have confirmed that cup-core probe is capable of detecting defects located at 8.0 mm below the surface in 12.0 mm thick stainless steel plates as well as simulated sub-surface localised corrosions. A linear relationship between phase angle and defect depth below the surface has been observed, apart from discrimination of subsurface and surface defects. [ABSTRACT FROM AUTHOR]