40th Magnetic Materials Center Seminar
March 15, 2007, 9:00
7th floor seminar room, Sengen
Material search by adding fourth elements in Heusler alloys
T. Nakatani
Despite some of Co-based Heusler alloys are said or predicted to be half-metals, in which only up-spin electrons contribute the electronic conductivity, the measured values of spin polarization by the point contact Andreev reflection (PCAR) method are always around P=0.55-0.60. This disappointing decay of spin polarization may result in presence of disordering in L21 ordered structure. One possible way to overcome this decay is to obtain materials tolerant to disordering by changing the position of the Fermi level in the minority gap.
In our recent works, we made and investigated two kinds of quaternary Heusler alloys which have been predicted to be hopeful materials by first principle calculations, they are Co2MnxFe1-xSi series (x=0.25, 0.4, 0.5, 0.75) and Co2FeGa0.25Si0.75. Disappointingly Co2MnFeSi series didn’ t have a dependence of the spin polarization on composition, that is, the P value didn’t change for different composition. On the other hand, Co2FeGa0.25Si0.75 alloy showed somehow higher spin polarization (P=0.59-0.60) than that in Co2FeSi (P=0.57). According to the calculation by Dr. Gercsi, A2 type disorder (between X and Z element, Co-Ga, Co-Si substitution) destroys the half-matallicity immediately. Thus it is important to improve B2 ordering not but L21. In this seminar I will discuss how to improve value of intrinsic spin polarization.