Area dependence of high-frequency spin-transfer resonance in giant magnetoresistance contacts up to 300nm diameter

We measured high-frequency spin-transfer resonances from <8GHz to >26GHz excited by dc currents through giant magnetoresistance point contacts with diameters d from <50 to almost 300nm. The slope of resonance frequency versus current decreased with increased d and was fit best by a spin-transfer model where the effective d extends ⩾50nm past the contact edge into the surrounding magnetic film. An increased resonance critical current versus contact area was also fit well by this model including a surrounding ring of excited area. Spin-transfer resonance in large devices eliminates the need for electron-beam lithography in applications.