Xd. Zhang et al., MAGNETORESISTANCE AND EXCHANGE COUPLING IN A FERROMAGNETIC TUNNEL JUNCTION WITH FERROMAGNETIC LAYERS OF FINITE THICKNESS, Physical review. B, Condensed matter, 57(2), 1998, pp. 1090-1096
Based on a two-band model, we investigate the tunnel magnetoresistance
(TMR) and interlayer exchange coupling (IEC) in a ferromagnet/insulat
or (semiconductor)/ferromagnet [FM/I(S)/FM] tunnel junction covered on
both sides by nonmagnetic metal layers. Our results show that (1) the
TMR oscillates with the thickness of ferromagnetic layers and can rea
ch very large values under suitable conditions, which may in general n
ot be reached in a FM/I(S)/FM tunnel junction with an infinitely thick
ferromagnetic layer. This suggests an alternative way to obtain large
TMR; (2) the bilinear coupling (J(1)) and biquadratic coupling (J(2))
decrease exponentially with the increase of barrier thickness, wherea
s they oscillate with the thickness of the FM layer, and J(2)/J(1) can
reach considerably large values under some conditions; (3) the oscill
ations of the IEC and the TMR with the FM layer thickness are correlat
ed owing to the quantum-size effect namely, the oscillation period and
phase of the TMR are exactly the same as that of the IEC, Furthermore
, the quantum-size effect can also give rise to a positive TMR (invers
e spin-valve effect).