4th Metallic Nanostructure Group Seminar
December 22, 2005, 9:00 am
7th floor seminar room, Sengen
Precipitation hardening behavior of Mg-Sn alloy
Taisuke Sasaki
Magnesium alloys are very attractive as structural components in train, automotive and aerospace industries because of their light weight. In order to spread the usage of magnesium alloy, it is necessary to improve their mechanical properties, especially the strength. Up to now, many attempts to improve the mechanical properties have been made. The enhancement of mechanical property is carried out mainly by grain refinement, texture control and controlling the distribution of second phase particles. Precipitation hardening behavior, one of the well known strengthening concepts, has been rarely applied to the commercial alloys. Precipitation hardening behavior or magnesium alloy has been observed in many alloy systems such as Mg-RE and Mg-Ca, Mg-Zn alloy system etc. This phenomenon is interesting not only industrially but also scientifically. Mg-Sn alloy is one of the promising alloy systems which can show the precipitation hardening behavior. In fact, however, very few studies have been carried out concerning the precipitation behavior of this alloy system even the microstructure observation by Transmission Electron Microscopy (TEM). It has been found that the precipitation hardening behavior of Mg-Sn alloy has been greatly enhanced by the addition of X. In the present talk, the effect of X on age hardening behavior will be presented together with the other conventional way to improve the mechanical properties of magnesium alloy.

Toward the narrow size distribution of FePt particles for perpendicular recording media
Tomoko 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 10 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 films 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.

Heusler alloys and their role in Spintronics
A. Rajanikanth
The research on data storage systems both on recording media as well as on read heads is heading towards achieving high-density data storage, memory and effective read heads. Especially spintronics is a growing research topic for realizing read heads for high density recording media. The basic principle of spin electronics is “current flowing in a semiconductor is mainly charge dependent where as in half-metals the current flowing is both charge and spin dependent”, making it to be a versatile technique for control of charge flow in electronic devices. The spin-polarized transport give rise to magnetoresistance that is, the conduction is dependent on external magnetic field. The tunneling magnetoresistance (TMR), gaint-magneto resistance (GMR) especially in the form of thin films employed for a number of uses, from sensors in memory chips to non-volatile thin film computer memory and high density read heads. Half-metals are of the most promising materials for spintronic devices because of their high magnetoresistance property. The current research on half-metals is mainly to get 100% spin-polarization in order to achieve high TMR ratio, which promises for application. However, the present scenario in this field is, experimentally spin-polarization is only about 50-70%. Therefore, the need for studying on half-metals in more detail both microstructurally and physically gained importance. Heusler alloys are one among such half-metals, e.g. Co2MnSi and Co2MnGe,etc These alloys have high ordering temperatures, high Tc, and low coercivity. The microstructural, magnetic and spin transport by the point-contact Andreev reflection (PCAR) technique on these alloys will be presented.