Shape induced magnetic vortex state in hexagonal ordered cofe nanodot arrays using ultrathin alumina shadow mask

Highlights: • Effect of t_d in hexagonal ordered CoFe nanodot arrays grown inside UTAM was studied. • Magnetic vortex states via pinched neck was obtained at _d = 20 nm in CoFe nanodots. • UTAM shadow effect is influencing the magnetic properties of CoFe nanodot arrays. • Vortex nucleation/annihilation field was dominated by the shape of the nanodots. • Micromagnetic simulation studies confirmed the shape effect of CoFe nanodot arrays. The magnetization reversal process of hexagonal ordered CoFe nanodot arrays was investigated as a function of nanodot thickness $\left(t_d\right)$ varying from 10 to 30 nm with fixed diameter. For this purpose, ordered CoFe nanodots with a diameter of 80 ± 4 nm were grown by sputtering using ultra-thin alumina mask. The vortex annihilation and the dynamic spin configuration in the ordered CoFe nanodots were analyzed by means of magnetic hysteresis loops in complement with the micromagnetic simulation studies. A highly pinched hysteresis loop observed at 20 nm thickness suggests the occurrence of vortex state in these nanodots. With increase in dot thickness from 10 to 30 nm, the estimated coercivity values tend to increase from 80 to 175 Oe, indicating irreversible change in the nucleation/annihilation field of vortex state. The measured magnetic properties were then corroborated with the change in the shape of the nanodots from disk to hemisphere through micromagnetic simulation.