  Formation of bright envelope solitons from wave packets with a repulsive
nonlinearity was observed for the first time. The experiments used surface
spin-wave packets in magnetic yttrium iron garnet (YIG) thin film strips. When
the wave packets are narrow and have low power, they undergo self-broadening
during the propagation. When the wave packets are relatively wide or their
power is relatively high, they can experience self-narrowing or even evolve
into bright solitons. The experimental results were reproduced by numerical
simulations based on a modified nonlinear Schr\"odinger equation model.
