8th Metallic Nanostructure Group Seminar
February 09, 2006, 9:00 am
7th floor seminar room, Sengen
Toward the narrow size distribution of FePt particles for perpendicular recording media
T. O. Seki
For achieving higher areal density in the perpendicular recording system, high signal to media noise ratio (SNRm) must be maintained without degrading the thermal stability of nanosized particles. Since the size of magnetically isolated particles is expected to become 7 nm for the area density of 1 Tb/inch2, L10 ordered FePt receives intense research interest for its very high magnetocrystalline anisotropy. The size and size distribution of the particles is also known to have a crucial effect on recording properties. The magnetic thin film with the narrow size distribution is expected to reduce the thermal decay problem. Although many investigations have reported the fabrication of FePt nanoparticles with narrow size distributions by chemical method, employment of the sputtering process is more desirable for commercial applications. However, there is no report of successful processing of FePt nanoparticle arrays with narrow size distributions with the sputtering method. In this talk, I report my recent attempts to reduce the grain size distribution of FePt thin films that were sputter deposited on Cu underlayers on MgO substrates. There is a lattice mismatch of 6.2% between L10-FePt(001) and Cu(100). Therefore forming island structure is expected by a relaxation of lattice mismatch.

Magnetization process of Co-Pd-Si-O nanogranular soft magnetic film studied by Polarized Small-Angle Neutron Scattering (Po-SANS)
M. Ohnuma
Metal-nonmetal nanogranular soft-magnetic film is one of the most promising soft-magnetic materials in high-frequency region due to their high-Bs, large electric resistivity and large induced magnetic anisotropy (Hk). The induced anisotropy is almost ten times larger than one which can be induced in conventional nanocrystalline soft magnetic materials like FINEMET. Because it is difficult to explain such large anisotropy by well-known Néel-Taniguchi theory, some new mechanisms must be underlying in it. For making it clear, we are studying the response of magnetic domain structure in the field which is smaller than Hk using Po-SANS which has been firstly installed in JAEA in last October. I will report a preliminary result of Po-SANS measurements. 

Study of dual amorphous phase formation in metallic glasses
B. Srinivasa Rao
Bulk metallic glass composites are gaining much importance because of their improved properties such as high strength and improved ductility. This is achieved by in-situ formation of crystallites or ex-situ reinforcement. Recently, Kuendig et al. experimentally demonstrated the formation of two amorphous phases in a multicomponent metallic glass. This observation opens a new field of composites composed of two glassy phases that may exhibit some interesting properties. The two phase amorphous structure has been mostly observed in alloy systems containing elements with a positive heat of mixing. On the contrary, the present work focuses on the possibility of achieving two phase amorphous structure with elements having negative heat of mixing as predicted by thermodynamic models. In my presentation, I will discuss thermodynamics of several alloy systems that exhibit a miscibility gap despite having negative heat of mixing among the constituents.