10 - Current-induced dynamics of chiral domain walls in magnetic heterostructures

Abstract

We have studied the current-induced dynamics of chiral magnetic domain walls in CoFeB | MgO heterostructures with various heavy metal (HM) underlayers. The domain wall velocity is studied as a function of magnetic field, the amplitude and length of the current pulse that flows in the heterostructure to reveal the characteristics of homochiral Neel domain walls. We find that the domain wall moves along or against the current flow depending on the HM layer material, suggesting that the magnetic chirality of the CoFeB layer depends on the combination of the materials used at the HM/ferromagnetic metal (FM) layer interface. For homochiral Neel walls, we find the wall velocity increases with decreasing pulse length for a time scale below 20ns. Model calculations including micromagnetic simulations suggest that the time needed to accelerate and decelerate the current-induced motion of chiral domain walls is different. Moreover, a universal short-range repulsion is found among chiral domain walls. The distance between two neighboring chiral domain walls can be reduced with application of out of plane field and allows formation of coupled domain walls. We show that current pulses can move a large number of coupled domain walls synchronously. These results show the unique features of the current-induced dynamics of chiral domain walls in technologically important thin film heterostructures for novel storage class memories.