24th Magnetic Materials Center Seminar
September 25, 2006, 10:30
7th floor seminar room, Sengen
Microstructure and Mangetic properties of FePt films for Pinning Media
Y. K. Takahashi
L10-FePt has received much attention for the high density magnetic recording media, because its magnetocrystalline anisotropy(Ku) is extremely high. However, the magnetic flux of currently used write head is not enough for saturation writing due to the high Ku of L10-FePt. Pinning media is one of the candidates for writable media. It is proposed as a scheme to significantly reduce irregularities in recorded transition boundaries without thermal instability.
Since the magnetic properties are depending on the microstructure, the control of the pinning sites is important for obtaining good magnetic properties. We introduce grain boundaries, nonmagnetic inclusion and twins which can be act as pinning sites in the L10-FePt continuous films.
In this talk, I will present the advantage point of the pinning media and preliminary results.

GMR of spin valves using Heusler alloys
T. Furubayashi
Giant magnetoresistance (GMR) of three-layered thin films with the FM/NM/NM (FM: ferromagnetic metal, NM: non-magnetic metal) structure has been extensively investigated for both current-in-plane (CIP) and current-perpendicular-to-plane (CPP) geometries. Comparing with tunneling magnetoresistance (TMR) devices, where the FM/I/FM (I: insulator) three-layered structure is utilized, CPP GMR devices are expected to achieve lower electrical resistance, leading to faster response time when applied for magnetic reading heads. At the present, however, MR ratio of CPP GMR devices is still much lower than that of TMR. It is highly desired to achieve high MR ratio in CPP GMR. One possible clue for this is to utilize Heusler alloys, which have high spin polarization.
Samples for studying CIP GMR require much less processes to fabricate comparing with CPP devices. Thus, we started the study of GMR using Heusler alloys with CIP GMR. In this talk, I describe our preliminary results after a brief review of this field.

Bulk and tunneling spin polarizations
K. Hono
We have been successful in measuring bulk spin polarizations of ferromagnetic materials by point contact Andreev reflection (PCAR) method. The experimental data obtained so far show good match with the literature values, and in some cases, the spin polarization measured by PCAR was found to be in fair ageement with the value deduced from TMR values of magnetic tunneling junctions (MTJ). However, some critical comments were made on our results saying it was merely a lucky coincidece.
In this talk, I will briefly review the spin polarization measurements by PCAR and superconductor tunneling spectroscopy (STS) and propose the future direction of our work. While PCAR is useful for search of half-metals, STS should be introduced to measure tunneling spin polarizations. The comparison of P and P will become a very powerful tool to develop MTJs with high TMR values.