Jan 12, 2009
FePt nanoparticles in silica films for data storage
The increased recording density of data storage devices has led to the continuous decrease of magnetic bit volume into nano-size range. However, there is a fundamental barrier to further reduce the size of written bits due to the superparamagnetism phenomena, which causes the loss of the data immediately after the writing process. One of the solutions to this issue is to choose magnetic materials with higher magnetocrystalline anisotropy, Ku.
FePt and CoPt nanoparticle assemblies with the L10 structure have been considered as building blocks for fabricating next generation information storage media. The high Ku values of L10 FePt and its high chemical stability help decrease the size limit for the onset of superparamagnetism. However, the as-prepared FePt nanoparticles are normally A1 phase that has low Ku. A post-synthesis annealing process at above 600 degC is required to obtain the high-Ku L10 phase. Annealing to such high temperatures is undesirable because of coalescence and loss of positional order of nanoparticles in assembled fashion.
In a recent study, the authors combined the sol-gel preparation of silica and self-assembling process of FePt nanoparticles to form ordered particle arrays in silica thin films (see Fig. 1). Annealing the nanoparticles-in-film composite at 650 degC transforms the A1-phased FePt into L10 phase, yielding magnetic coercivity values Hc > 6300 Oe that signifies the high Ku value. The positional order of the particle array is retained due to the protection offered by the silica host. Such films with assemblies of high-coercivity magnetic particles can be an important step toward realizing new types of ultra-high-density data storage devices.
Under current experimental process, the domain size of the particle assembly is still relatively small. Large-area ordered particle assembly is desired for the data storage applications. The researchers are working on the understanding of the details to further improve this composite film fabrication process to allow large scaled assembly of FePt particles in silica films. They are also targeting on controlling the alignment of the crystalline orientation of FePt particles in the silica films to allow the reading process carried out on the films.
About the author
The work was performed at Rensselaer Polytechnic Institute, USA, Nanyang Technological University, Singapore and Nanjing University, China. Prof. Qingyu Yan is an assistant professor in School of Materials Science and Engineering in Nanyang Technological University, Singapore. Dr. Arup Purkayastha is a research scientist in Laird Technologies, India. Dr. Amit P. Singh is currently a research engineer in Intel Corporation. Dr. Huafang Li is a postdoctoral research in the physics department of Rensselaer Polytechnic Institute. Prof. Aidong Li is a professor in Materials Science and Engineering Department of Nanjing Unviersity, China. Prof. Raju V. Ramanujan is an associate professor in School of Materials Science and Engineering in Nanyang Technological University, Singapore. Prof. Ganapathiraman Ramanath is a professor in Materials Science and Engineering Department of Rensselaer Polytechnic Institute, USA.