  We study the interactions between oscillating non-resonant rf fields and
atoms with strong spin-exchange collisions in the presence of a weak dc
magnetic field. We find that the atomic Larmor precession frequency shows a new
functional form to the rf field parameters when the spin-exchange collision
rate is tuned. In the weak rf field amplitude regime, a strong modification of
atomic Larmor frequency appears when the spin-exchange rate is comparable to
the rf field frequency. This new effect has been neglected before due to its
narrow observation window. We compare the experimental results with density
matrix calculations, and explain the data by an underdamped oscillator model.
When the rf field amplitude is large, there is a minimum atomic gyromagnetic
ratio point due to the rf photon dressing, and we find that strong
spin-exchange interactions modify the position of such a point.
