High Energy Density Pulsed Plasmas in Plasma Focus: Novel Plasma Processing Tool for Nanophase Hard Magnetic Material Synthesis

This paper presents the review of the applications of pulsed high energy density pinch plasmas (with energy densities in the range of 1-10 x 10(10) J/m(3)), accompanied by self generated energetic high flux instability accelerated ion beams, from a dense plasma focus device in nanophase material synthesis, in particular the magnetically hard nanoparticle thin films with possible applications in high density magnetic data storage. The plasma focus device, a non-cylindrical z-pinch device, being a multiple radiation source of ions, electron, soft and hard X-rays, and neutrons, has routinely been used for several applications such as lithography, radiography, imaging, activation analysis, radioisotopes production and more recently for material processing and thin films depositions. This review paper highlights and critically discusses the key features and traits (such as the plasma dynamics, plasma characteristics and energetic ions and electron emission characteristics) of plasma focus device to understand the novelties, opportunities and mechanisms of processing and synthesis of nanophase hard magnetic materials using this device. The results of recent key experimental investigations performed on the modification of various physical properties of PLD grown thin films of FePt by energetic ion exposure in plasma focus device and the deposition of nanostructured CoPt thin films in plasma focus device are reviewed. The FePt and CoPt thin films are believed to be the most prominent candidates for ultra-high density magnetic data storage. The prime requirements for ultra-high density magnetic data storage are: (i) small size of nanoparticles in the range of similar to 3-4 nm with narrow size distribution (ii) nanoparticles should be in fct phase, which is achieved by post synthesis annealing at about 600 degrees C, with high magnetocrystalline anisotropy (K-u) to overcome the superparamagnetism, and (iii) reduced exchange coupling effects with well-separated distribution of nanoparticles. The reduction of phase transition temperature for transformation from low K-u fcc-structured magnetically soft A1 phase to high K-u fct-structured magnetically hard L1(0) phase, control of the fct-(001) orientation of thin films and minimizing grain growth are three key challenges for practical application of FePt and CoPt nanoparticle thin films in data storage These technologically challenging issues were successfully resolved, to some extent, using novel high energy density plasmas of plasma focus device.