Half-metallic electronic structure of Co2(Mn, Fe)Si electrodes investigated through tunneling spectroscopy for fully epitaxial magnetic tunnel junctions

Our purpose in the present study was to elucidate the origin of the giant TMR ratio of Co
₂
(Mn,Fe)Si (CMFS) MTJs with lightly Fe-doped, Mn-rich CMFS electrodes. We took into consideration the valence electron number/f.u., Z
_t
, of off-stoichiometric Co
₂
MnSi (CMS) expressed as Co
₂
Mn
_α
Si
_ß
decreases with increasing α from an Mn-deficient composition to an Mn-rich composition according to the antisite-based formula composition model [5]. The E
_F
position would generally shift to the lower energy side in the half-metal gap with increasing α and finally cross the minority-spin valence band edge . On the other hand, the Z
_t
value is increased by substituting Fe for Mn in CMS. First-principles calculations of Co
₂
(Mn
_1-x
Fe
_x
)Si predicted that the E
_F
position in the half-metal gap of these materials generally would shift to the higher energy side with an increase in x [6,7].