146th Magnetic Materials Center Seminar
September 21, 2010, 9:00-
7th floor small seminar room, Sengen
Enhanced precipitation hardening of Mg alloy by Al addition
J. Jayamani
The combinations of oversized element like RE and Ca and undersized element like Zn in Mg causes the formation of plate like precipitates on the basal plane. Both Mg-RE-Zn and Mg-Ca-Zn alloys exhibit age hardening response and good creep properties, which are attributed to the formation of plate like GP zones. It is intriguing to see whether or not other undersized elements like Al exhibit the similar effect. Thus, the effect of Al additions in a Mg-0.5Ca(wt.%) alloy on age hardening responses have been investigated. The Mg-0.5Ca-0.3Al alloy showed peak hardness (72 HV) higher than that for the Mg-1Ca-1Zn alloy. TEM and 3DAP analyses confirmed the dense distribution of ordered G.P. zones on the basal planes and the subsequent formation of Al2Ca causes the over-aging.

Tunnel magnetoresistance enhancement in fully epitaxial Fe/Mg-Al-Ox/Fe Junctions
H. Sukegawa
The MgAl2O4 barrier is advantageous because of its nondeliquescence and its small lattice mismatch with typical bcc-Fe(Co) alloys and Co-based Heusler alloys (~ 1%). Therefore an achievement of perfect lattice-matched structure with defect-free barrier interfaces is expected in MgAl2O4-based MTJs. In this study I report magnetic tunnel junctions (MTJs) with spinel-type epitaxial barrier MgAl2O4. The barrier was prepared using plasma oxidation of an Mg/Al bilayer or MgAl2 layer. Large TMR ratio was obtained in an optimized Fe/MgAl2O4/Fe MTJ (178% at 300 K and 296% at 16K), indicating TMR enhancement by coherent tunneling effect.