Soft magnetism of Fe-Co-N thin films with a Permalloy underlayer

A systematic investigation was carried out on the Fe-Co-N thin films with varying Permalloy underlayer thicknesses (in short Py\Fe-Co-N films), which show significantly improved magnetic softness when a very thin Permalloy underlayer is applied. The easy axis coercivities of the Py\Fe-Co-N films drop from 1.3 kA/m (16 Oe) to 640 A/m (8 Oe) with an appropriate Permalloy underlayer; and the corresponding hard axis coercivity drops from 320 A/m (4 Oe) to less than 80 A/m (1 Oe). The highest transverse permeability is observed in the Py\Fe-Co-N film with a Permalloy underlayer of 3.5 nm, which also shows the smallest dispersion angle alpha(50) among the Py\Fe-Co-N films. The changes in the mean grain size, texture, and magnetostriction are determined to not be responsible for the observed magnetic softness in the Py\Fe-Co-N films. In contrast, a tantalum underlayer does not reduce the coercivities and dispersion angles in the Ta\Fe-Co-N films. Based on these results, an exchange-induced ripple reduction mechanism is proposed to explain the effects of the Permalloy underlayer on the Py\Fe-Co-N films. (C) 2002 American Institute of Physics.