  Energy gaps have been measured for the ferromagnetic quantum Hall effect
states at v=1 and 3 in GaAs/GaAlAs heterojunctions as a function of Zeeman
energy, which is reduced to zero by applying hydrostatic pressures of up to
20kbar. At large Zeeman energy the gaps are consistent with spin wave
excitations. For a low density sample the gap at v=1 decreases with increasing
pressure and reaches a minimum when the g-factor vanishes. At small Zeeman
energy the excitation appears to consist of a large number of reversed spins
and may be interpreted as a Skyrmion. The data also suggest Skyrmionic
excitations take place at v=3. The width of the minimum at v=1 is found to
decrease as the g-factor is reduced in a similar way for all samples.
