Rapid tuning of Ni81Fe19/Au bilayer magnetic properties by focused ion beam intermixing

Magnetic properties of in-plane magnetized bilayers are investigated as a function of 30 keV Ga+ ion dose and Ni81Fe19 layer thickness. Coercivity, saturation magnetization, hard axis anisotropy field, and hysteresis loop remanence ratio are tuned at low-ion doses. The magnetic properties of irradiated bilayers are found to be very sensitive to Ni81Fe19 layer thickness. Specifically, the critical ion dose for room temperature quenching of measured ferromagnetism in capped Ni81Fe19 samples is found to be proportional to the square root of Ni81Fe19 layer thickness. This square root dependence is consistent with a structural change due to radiation-induced displacement of interfacial atoms. Focused ion beam (FIB) intermixing can rapidly modify the magnetic properties of ultrathin in-plane magnetized capped films at lower ion doses than surface sputtering or ion implantation effects.