Magnetic Hysteresis Induction with Nanocolumnar Defects in Magnetic Insulators

The magnetic property modification of an easy-plane magnetic insulator caused by an accumulation of nanocolumnar defects along the film normal was investigated using numerical simulations and heavy-ion beam irradiation experiments. Micromagnetic simulations suggest that depending on the density of the nonmagnetic nanocolumnar defects, the microstructure of fragmented ferromagnetic domains is formed, leading to magnetic coercivity enhancement and magnetization reduction. To prove this prediction, gold ions with 300 MeV were used for the irradiation to create amorphous nanocolumnar defects in crystalline bismuth-doped lutetium iron garnet (Bi:LuIG) films. With an increase in the ion irradiation dose, modifications in the saturation magnetization and magnetic coercivity were observed in an uncorrelated manner; the enhancement of magnetic coercivity exhibited a fluence threshold, whereas the decrease in saturation magnetization caused by ion-beam damage was monotonic with increasing beam fluence. These behaviors qualitatively agree with the numerical simulations and models based on the continuum percolation theory. Because the irradiation effects were controlled by the beam fluences, the present method has the potential to be a microstructuring technique for magnetic insulators.