Aharonov-Bohm Oscillation in Rings with Permalloy

Aharonov-Bohm (A-B) rings with and without an inserted permalloy rod were fabricated from an AlGaAs/GaAs two dimensional electron gas (2DEG) wafer. The permalloy was a soft ferromagnetic alloy metal with a relative permeability µ of about 104, so that the effective susceptibility, including the demagnetizing effect, could be calculated from only the diameter and height of the permalloy rod. Magnetoresistance of the A-B rings with and without the permalloy rod was measured at T = 0.3 K using an external magnetic field. The magnetoresistance had oscillations of different periods in the two cases. The main oscillation periods of the rings with and without the permalloy rod were 7.5 Oe and 28 Oe, respectively, clearly indicating that the permalloy rod reduced the oscillation period. The reduction factor (26%) was consistent with the demagnetizing effect of the permalloy rod. If the permalloy rod is designed to be free of the demagnetizing effect, the reduction factor should reach the order of the reciprocal of relative permeability µ.