Frequency dependence of the radio frequency collapse effect

A systematic study of the dependence of the radio frequency (rf) collapse effect on the frequency of the rf field which induces the fast relaxation of the hyperfine field was performed for Permalloy and amorphous Fe₄₅Ni₃₀Si₁₀B₁₅ alloy. The rf collapse was studied for the frequency range of 12 MHz to 64 MHz. The results show that the rf collapse appears gradually in both materials as the rf field frequency exceeds the Larmor frequency what is in agreement with the model predictions.