Spin vortex states and hysteretic properties of submicron size NiFe elements

Micromagnetic structures in submicron size circular permalloy elements of v arious thickness (5-50 nm) have been experimentally studied using a magneti c force microscope (MFM). One and two vortex micromagnetic states were obse rved in the elements. It was found that one vortex state is more favorable under external field of low values, while two vortex state forms under high fields. Switching between one and two vortex states results in a hysteresi s in the micromagnetic response of the elements. The transition field from one to two vortex state increases with the increase of element thickness an d, therefore, with the increase of the demagnetizing effect of the element edges. The two vortex state was not observed in the elements with a thickne ss of 50 nm or greater. The micromagnetic behavior correlates with hysteres is loops of a free layer in a magnetic tunnel junction of size, shape, and free layer thickness similar to elements examined with the MFM. (C) 2000 Am erican Institute of Physics. [S0021-8979(00)74408-2].