28th Magnetic Materials Center Seminar
November 6, 2006, 10:30
7th floor seminar room, Sengen
TEM observation for (001) oriented L10 FePt on NiTa seed layer exposed to O2
T. O. Seki
For applications of FePt in the perpendicular recording system, c-axis alignment of L10-FePt is required to be the perpendicular direction to the film plane. Recently, Maeda reported highly 001 oriented FePt films on amorphous NiTa seed layers exposed to oxygen properly [1]. The purpose of this work is to clarify the structural difference of the films depending on the amount of O2 exposure and the role of O2 exposure on the crystallographic texture of L10-FePt by detailed TEM. C(7)/FePt (10)/Pt(20)/Cr(5)/NiTa(25 nm) films were deposited on glass substrates by a sputtering system. The NiTa amorphous seed layer was exposed to oxygen gas. Fig. 1 shows magnetization curves of the FePt films on NiTa layers exposed to O2, (a) 0 L, (b) 1.9 ´ 102 L and (c) 3.7 ´ 103 L, which was reported in [1]. In the film of (a) and (c), the orientation is not perpendicular to the film completely because the in-plane magnetization curve shows hysteresis loss. The in-plane magnetization curve of the film optimized O2 exposure of (b) shows no Hc and straight line, and the perpendicular curve shows good squareness and large Hc of 7 kOe. To investigate this phenomenon, the structure of each layer on the NiTa seed layer was investigated.
[1] T. Maeda, IEEE Trans. Magn., vol. 41, pp. 3331-3333, (2005)

Structure, magnetic properties and Spin polarization of Co2(CrFe)Si Heusler alloys
S. V. Karthik
The most promising half metallic materials for spintronic applications are L21 type Co-based Heusler alloys with high spin polarization and Curie temperature. It has been reported that Co2FeSi has the highest Curie temperature among Heusler alloys. The band structure calculation suggests 100% spin polarization (P = 1), with a finite gap in minority density of states (DOS) and small majority DOS at Fermi level. However, spin polarization of Co2FeSi was measured to be 0.55±0.02 by point contact Andreev Reflection (PCAR). In this work, we studied the effect of Cr addition on the structure, magnetization and spin polarization of quaternary Co2CrxFe1-xSi alloys.