Synthesis of improved magnetic and ferroelectromagnetic materials by structure manipulation at nanometer level

I-7: Synthesis of improved magnetic and Ferroelectromagnetic materials by structure manipulation at nanometer level

T. Sritharan, A. Srinivas and F.Y.C. Boey School of Materials Engineering, NTU

Abstract

The magnetic property arises principally from electron spin of elemental atoms while the ferroelectric property arises from crystal structure distortion that provides two possible lattice points for certain ions. Further, the magnetic permeability could be increased by having a nanocrystalline structure where the crystallite size is smaller than the ferromagnetic exchange length. Work had been in progress at SME in two fronts: (i) Producing nanocrystalline ferromagnetic materials for use as soft magnets of high permeability. (ii) Synthesizing new materials with concurrent ferroelectric and magnetic properties. In the former, considerable progress has been made in alloy and process development to produce an improved nanocrystalline material based on Fe-Si alloy system. Some of these will be presented. The current challenge is to densify the nanocrystalline alloy powder into a solid product without losing the nanocrystalline structure. This requires further study of the consolidation processes and alloy development to arrest grain growth. This is a universal problem in all nanocrystalline materials as high temperature excursions cause rapid grain growth because of the high energy state of the material. The ferroelectromagnetic material project recently begun is a spin-off from the first project. The same experimental technique could be used to produce new, complex ceramics. We have successfully induced magnetic moment into a conventional ferroelectric material by selective substitution of ions in the crystal structure. This is different to epitaxial growth because we attempt to manipulate polycrystalline, bulk materials. Such nanoscale manipulation is being done with computational materials modeling and experimentation. Designing ferroelectromagnetic materials from fundamental principles is possible as one property is crystal structure dependent while the other is electronic structure dependent with, apparently, little cross interference. Future work will be directed towards improving the properties to useful levels and producing in thin film form for applications in electronics devices.