1111.5582 (A. Moor et al.)

Josephson-like spin current in junctions composed of antiferromagnets
and ferromagnets    [PDF]

A. Moor, A. F. Volkov, K. B. Efetov

We study Josephson-like junctions formed by materials with antiferromagnetic
(AF) order parameters. As an antiferromagnet, we consider a two-band material
in which a spin density wave (SDW) arises. This could be Fe-based pnictides in
the temperature interval ${T_{\text{c}}\leq T\leq T_{N}}$, where $T_{c}$ and
$T_{N}$ are the critical temperatures for the superconducting and
antiferromagnetic transitions, respectively. The spin current $j_{\text{Sp}}$
in AF/F/AF junctions with a ballistic ferromagnetic layer and in tunnel AF/I/AF
junctions is calculated. It depends on the angle between the magnetization
vectors in the AF leads in the same way as the Josephson current depends on the
phase difference of the superconducting order parameters in S/I/S tunnel
junctions. It turns out that in AF/F/AF junctions, two components of the SDW
order parameter are induced in the F\nobreakdash-layer. One of them oscillates
in space with a short period ${\xi_{\text{F,b}} \sim \hbar v/\mathcal{H}}$
while the other decays monotonously from the interfaces over a long distance of
the order ${\xi_{\text{N,b}}=\hbar v/2\pi T}$ (where $v$, $\mathcal{H}$ and $T$
are the Fermi velocity, the exchange energy and the temperature, respectively;
the subindex $\text{b}$ denotes the ballistic case). This is a clear analogy
with the case of Josephson S/F/S junctions with a nonhomogeneous magnetization
where short- and long\nobreakdash-range condensate components are induced in
the F\nobreakdash-layer. However, in contrast to the charge Josephson current
in S/F/S junctions, the spin current in AF/F/AF junctions is not constant in
space, but oscillates in the ballistic F\nobreakdash-layer. We also calculate
the dependence of $j_{\text{Sp}}$ on the deviation from the ideal nesting in
the AF/I/AF junctions.

View original: http://arxiv.org/abs/1111.5582