Bias susceptibility measurements in thin permalloy films

Susceptibility measurements at 5000 Hz have been performed in the easy and hard directions on two 80-20 Permalloy films (1000 Å, 1 cm in diameter) cut from large samples. The experimental results agree with the predictions of the Hoffmann theory. The susceptibility parallel to the average direction ofMis found to be proportional to1/(H - H_{k})^{7/4}or1/(H_{k} - H)^{7/4}when the net field is large enough to prevent blocking.