Spin waves in exchange-biased NiFe/IrMn circular nanorings

We present the experimental investigation of the static and dynamical properties of NiFe(20 nm)/IrMn(5 nm) rings. Magneto-optic Kerr effect measurements show that the IrMn introduces a sizable exchange-bias field H-EB approximate to 80 Oe, which shifts the hysteresis loop along the excange-bias direction. Measured loops were satisfactorily reproduced using a micromagnetic calculation which includes the presence of H-EB. Measurement of high frequency normal modes, by Brillouin light scattering, shows that the presence of the IrMn layer causes an overall up-shift of the spin wave frequency, in qualitative agreement with pervious studies of other exchange-biased systems. Moreover, the frequency asymmetry of the spin wave frequency upon reversing the external field is quantitatively consistent with the presence of the exchange-bias field measured by the Kerr effect. (c) 2008 American Institute of Physics.