  We study parametric instability in a magnomechanical system, specifically
examining magnon tunneling between moving ferromagnetic insulators. Our
analysis reveals that quantum fluctuations generate spin currents above a
critical velocity threshold, while no spin currents occur below this threshold
at low temperatures. The critical velocity depends on magnon stiffness and
Zeeman energy. Approaching the threshold, the spin current becomes divergent,
linked to the PT-symmetry-breaking transition. This enhanced behavior could
offer sensitive measurements and signal amplification in quantum technology.
