Stripe domains in Permalloy films as observed by ferromagnetic resonance and magnetic force microscopy

C. A. RAMOS; E. VASSALLO; J. GÓMEZ; A. BUTERA

Buenos Aires, Argentina

Conferencia; "FCM2008-At the Frontiers of Condensed Matter"; 2008

Tandar - CNEA

In this work we present results on Permalloy thin films (50, 100 and 250nm) grown by sputtering onto glass substrates. For the thinnest film a single magnetic resonance line is observed when the field is applied along the film plane. The thicker films evidence two and three absorptions (100nm and 250nm respectively) for the same conditions. These multiple absorptions seem to be related to the observation of stripe-domains by magnetic force microscopy (MFM) in the thickest film, indicative of up-down modulation of the magnetization along the film normal. On the intermediate thickness (100nm) the only feature we were able to observe by MFM was a perpendicular instability with a vortex-like shape near a sample edge. Micromagnetic calculations (J. B. Youssef et al Phys. Rev. B (2004) 69, 174402) indicate that a small perpendicular anisotropy originates this perpendicular instability of the magnetization and the stripe-domains which develop above a critical thickness of about 280nm. These domains have been associated with multiple absorptions in the microwave range, as calculated by dynamic micromagnetism. Our experimental results indicate that the critical thickness is smaller than previously reported and that FMR present clear features of magnetization instabilities before the stripe-domains are formed.