Shape-induced ultrahigh magnetic anisotropy and ferromagnetic resonance frequency of micropatterned thin Permalloy films

Magnetic anisotropy Hk>200Oe was observed from bar-shaped Permalloy strips. The film was deposited on sputtered Cr seed layer by electroplating under ∼800Oe external magnetic field. Tiny degradation of Hk was observed after 30 min postannealing at 400 °C in the absence of external magnetic field. The Permalloy strip with in-plane aspect ratio of 40:1 showed the ferromagnetic resonance at ∼5.3GHz. The ferromagnetic resonance frequency and magnetic anisotropy decreased to ∼1GHz and ∼50Oe, respectively, as the in-plane aspect ratio reduced from 40:1 to 10:1. In comparison, Permalloy strips plated on combined Ti∕TiN seed layers did not show clear anisotropy features.