  Magnonics is a rapidly developing subfield of spintronics, which deals with
devices and circuits that utilize spin currents carried by magnons - quanta of
spin waves. Magnon current, i.e. spin waves, can be used for information
processing, sensing, and other applications. A possibility of using the
amplitude and phase of magnons for sending signals via electrical insulators
creates conditions for avoiding Ohmic losses, and achieving ultra-low power
dissipation. Most of the envisioned magnonic logic devices are based on spin
wave interference, where the minimum energy per operation is limited by the
noise level. The sensitivity and selectivity of magnonic sensors is also
limited by the low frequency noise. However, the fundamental question "do
magnons make noise?" has not been answered yet. It is not known how noisy
magnonic devices are compared to their electronic counterparts. Here we show
that the low-frequency noise of magnonic devices is dominated by the random
telegraph signal noise rather than 1/f noise - a striking contrast to
electronic devices (f is a frequency). We found that the noise level of surface
magnons depends strongly on the power level, increasing sharply at the on-set
of nonlinear dissipation. The presence of the random telegraph signal noise
indicates that the current fluctuations involve random discrete macro events.
We anticipate that our results will help in developing the next generation of
magnonic devices for information processing and sensing.
