  The formation of a Bose condensate of magnons in a perpendicularly magnetized
film of yttrium iron garnet under radio-frequency pumping in a strip line is
studied experimentally. The characteristics of nonlinear magnetic resonance and
the spatial distribution of the Bose condensate of magnons in the magnetic
field gradient are investigated. In these experiments, the Bosonic system of
magnons behaves similarly to the Bose condensate of magnons in the
antiferromagnetic superfluid 3He-B, which was studied in detail earlier.
Magnonic BEC forms a coherently precessing state with the properties of
magnonic superfluidity. Its stability is determined by the repulsive potential
between excited magnons, which compensates for the inhomogeneity of the
magnetic field.
