Phase evolution and magnetic properties of Al substituted yttrium iron garnet nanopowders and plasma-sprayed coatings

Aluminum-substituted yttrium iron garnet (Al-YIG) nanostructured powders were synthesized using a citrate–nitrate gel combustion process. Atmospheric plasma-spray (APS) technique was employed to spray deposit the combustion derived feedstock powders. Nevertheless incongruently melting YIG resulted into a two-phase microstructure, Al-YIG powder resulted into a nanostructured garnet single phase when sprayed through thermal plasma. Room temperature saturation magnetization (MS) and Curie temperature (TC) of the Al-YIG powders decreased as a function of increasing Al content. As-sprayed YFe3.8Al1.2O12 coating has a room temperature MS of 6.2 emu/cc and is increased to 7.3 emu/cc after post-deposition heat treatment at 1000 °C/1 h. Microstructural characteristics of single splats were analyzed in order to understand the feedstock effect on deposit.