Micro Magnetic Exchange Interaction Tensor and Magnetization Reversal of ${\rm L}1_{0}$ FePt Based Alloy Thin Film Nano-Structures

We investigate the effect of crystal symmetry driven tensor form of micromagnetic exchange stiffness A on switching properties of L1₀ FePt composite nano-structures. The exchange interaction term in micromagnetic energy functional have been constructed to capture the results of the first principle calculations for magnetic excitations in [001] and [100] directions. We find that out-of-plane (OP) exchange component (A_||) is about two times weaker as compared to the in-plane (IP) component (A_⊥). We study the effect of this difference between principal axis elements of A tensor on the M-H loops using micromagnetic simulations. We compare two cases for IP and OP exchange constants: (a) A_⊥ = A_|| (limited case) and (b) A_⊥ = 0.5 A_|| (based on ab-initio calculations), and find that the a thermal coercive force for 30 × 30 nm bi-layer rectangular dots differs for these two cases. Further, we find that the coercive force difference between two cases decreases as the external field goes from OP to IP.