  We study magnetic critical behavior in the Ashkin-Teller model with an
asymmetric defect line. This system is represented by two Ising lattices of
spins $\sigma$ and $\tau$ interacting through a four-spin coupling $\epsilon$.
In addition, the couplings between $\sigma$-spins are modified along a
particular line, whereas couplings between $\tau$-spins are kept unaltered.
This problem has been previously considered by means of analytical
field-theoretical methods and by numerical techniques, with contradictory
results. For $\epsilon > 0$ field-theoretical calculations give a magnetic
critical exponent corresponding to $\sigma$-spins which depends on the defect
strength only (it is independent of $\epsilon$), while $\tau$-spins
magnetization decay with the universal Ising value $1/8$. On the contrary,
numerical computations based on density matrix renormalization (DMRG) give, for
$\epsilon > 0$ similar scaling behaviors for $\sigma$ and $\tau$ spins, which
depend on both $\epsilon$ and defect intensity. In this paper we revisit the
problem by performing a direct Montecarlo simulation. Our results are in well
agreement with DMRG computations. We also discuss some possible sources for the
disagreement between numerical and analytical results.
