Co_(50)Fe_(25-x)Mn_xSi_(25)系列合金的结构、磁性和半金属性研究

Structural,magnetic and half-metallic properties of CoFeMnSi alloys

利用实验和能带计算相结合的方法,对介于两种预期的半金属Heusler合金Co2FeSi和Co2MnSi间的四元合金Co50Fe25-xMnxSi25的晶体结构、磁性、能带结构和半金属性进行了研究.采用考虑库仑相互作用的的广义梯度近似方法计算了系列合金的能带结构,通过与实验结果进行对比,揭示了成分变化过程中合金分子磁矩及原子磁矩的变化规律.研究发现,随着Mn含量的变化,Co50Fe25-xMnxSi25合金的保持了高有序的L21结构,由于Co和Mn原子磁矩随着Mn替代量的增加而降低,系列四元合金的分子磁矩呈线性下降趋势.在整个Mn替代Fe的成分范围内,由于Co,Mn和Fe之间的电子杂化作用,材料始终保持100%的自旋极化率,呈半金属态.费密能级从Co2FeSi半金属能隙的导带底下移至Co2MnSi能隙的中间.能隙宽度在中间合金处出现最佳值,这表明四元合金有可能成为具有更高自旋极化率和更强抗干扰能力的自旋电子学材料.

Compared with the experiment results,the atomic moment of Co50 Fe25-x MnxSi25 dependending on composition and half-metalic of these alloys have been investigated by GGA ＋ U method.It has been found that with the increase of Mn content,Co50 Fe25-x MnxSi25 alloys always maintain a high ordered L21 structure and the total moment of these alloys decrease linearly which is mainly attribute to the reduction of Co atomic moment.It has also been found that with the increase of Mn content,Co50Fe25-xMnxSi25 alloys maintain 100% spin polarization and Fermi level move from the edge of the energy gap to the middle of the energy gap while the gap-width has changed.