First-principles study of tunneling magnetoresistance in Fe/MgAl2O4/Fe(001) magnetic tunnel junctions
First-principles study of tunneling magnetoresistance in Fe/MgAl2O4/Fe(001) magnetic tunnel junctions
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DOI：
10.1103/physrevb.86.024426
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发表时间：
2012-07-20
影响因子：
3.7
通讯作者：
Shirai, Masafumi
中科院分区：
文献类型：
--
作者：
Miura, Yoshio;Muramoto, Shingo;Shirai, Masafumi
基于电子结构和弹道电导的第一性原理计算，研究了Fe/MgAl 2 O 4/Fe（001）磁性隧道结的自旋相关输运性质.计算得到的Fe/MgAl 2 O 4/Fe（001）MTJ的隧道磁电阻（TMR）比约为160%，远小于相同势垒厚度的Fe/MgO/Fe（001）MTJ的TMR比（1600%）。而在正常尖晶石MgAl 2 O 4的费米能级附近的能隙中存在具有Delta（1）对称性的倏逝态，表明Fe/MgAl 2 O 4/Fe（001）MTJ中可能存在大的TMR。Fe/MgAl 2 O 4/Fe（001）MTJ的小TMR比是由于Fe电极的面内波矢量（k（平行于））的二维布里渊区中的带折叠效应导致的少数自旋态中的新导电沟道。由于MgAl 2 O 4的面内晶胞尺寸是bcc Fe的原始面内晶胞尺寸的两倍，边界边缘的能带被折叠，并且与MgAl 2 O 4势垒中的Delta（1）倏逝态耦合的少数自旋态出现在k（平行于）= 0处，这显著降低了MTJ的TMR比。
We investigated the spin-dependent transport properties of Fe/MgAl2O4/Fe(001) magnetic tunneling junctions (MTJs) on the basis of first-principles calculations of the electronic structures and the ballistic conductance. The calculated tunneling magnetoresistance (TMR) ratio of a Fe/MgAl2O4/Fe(001) MTJ was about 160%, which was much smaller than that of a Fe/MgO/Fe(001) MTJ (1600%) for the same barrier thickness. However, there was an evanescent state with Delta(1) symmetry in the energy gap around the Fermi level of normal spinel MgAl2O4, indicating the possibility of a large TMR in Fe/MgAl2O4/Fe(001) MTJs. The small TMR ratio of the Fe/MgAl2O4/Fe(001) MTJ was due to new conductive channels in the minority spin states resulting from a band-folding effect in the two-dimensional Brillouin zone of the in-plane wave vector (k(parallel to)) of the Fe electrode. Since the in-plane cell size of MgAl2O4 is twice that of the primitive in-plane cell size of bcc Fe, the bands in the boundary edges are folded, and minority-spin states coupled with the Delta(1) evanescent state in the MgAl2O4 barrier appear at k(parallel to) = 0, which reduces the TMR ratio of the MTJs significantly.