  We study intersubband spin density collective modes in double-layer quantum
Hall systems at $\nu=2$ within the time-dependent Hartree-Fock approximation.
We find that these intersubband spin density excitations may soften under
experimentally accessible conditions, signaling a phase transition to a new
quantum Hall state with interlayer inplane antiferromagnetic spin correlations.
We show that this novel canted antiferromagnetic phase is energetically stable
and that the phase transition is continuous.
