Long-lived induction signal in yttrium iron garnet

The results of the experiments on an yttrium iron garnet film have been reported, demonstrating two types of long-lived free induction signals. The first type corresponds well to signals appearing because of the superfluid transfer of magnons, which was previously detected in antiferromagnetic superfluid $^3$He-B. The second, ultra-long-lived, signal also has a number of properties of coherent precession. However, it is fundamentally different from the ultra-long-lived signal in $^3$He-B. The mechanism of formation of the ultra-long-lived signal in yttrium iron garnet has not yet been theoretically explained.