Area-Dependence of High Frequency Spin-Transfer Resonance in GMR Contacts up to 300 nm Diameter

The area-dependence of spin-transfer resonance in giant magnetoresistance (GMR) contacts from 50-300 nm diameter d is measured in this paper. With increasing d , a decreasing slope df/dl of precession frequency vs. current and an increasing critical current I_c is found. The data is well fit by a model where the precessing region extends outside the contact by a ring of width delta~ 50 nm. A GMR film with a base electrode, a 20 nm Co₈₁Fe₁₉ fixed layer, a 6 nm Cu spacer layer, a 4.5 nm Ni₈₀Fe₂₀ free layer, and a cap. The point contacts were written by optical or e-beam lithography and formed through SiO₂ or hardened PMMA. The inset shows an SEM image of a nominally 60 nm diameter contact. A dc current I is applied to the contact using a high-frequency bias tee and microwave probe and measured the GMR frequency spectrum. A magnetic field ~1 T normal to the film saturated the free moment out-of-plane at I=0 and tilted the fixed moment ~30deg out-of-plane.