Energetics of complex spin textures in LSMO artificial spin ice structures

Abstract

The fundamental building blocks of artificial spin ice (ASI) systems are magnetic nanoislands designed for Ising-like single domain configurations magnetized along the nanoisland length due to shape anisotropy. The dipolar interaction between these macrospins serve as the basis for investigating geometric frustration in ASIs with a variety of array geometries ranging from square-like arrangements to quasicrystals. Using X-ray photoemission electron microscopy (X-PEEM) to perform magnetic domain imaging, we studied thermally demagnetized La0.7Sr0.3MnO3-based brickwork ASIs and showed that non-Ising domains, which we call complex spin textures (CSTs), can be stabilized through appropriate selection of nanoisland width, W, and ASI lattice parameter, a. While W-dependent formation of CSTs can be explained due to the dominance of shape anisotropy, the a-dependence was unexpected for nanoislands possessing identical W, suggesting that inter-island effects play an important role. MuMax3 micromagnetic simulations indicated that an intermediate range of 100 nm ≤ W < 150 nm and 600 nm ≤ a ≤ 700 nm exists where the formation of Ising states are preferred over CSTs as shown in Fig. 1. For larger values of W and a that reside above the black border in the energy diagram of Fig. 1, CST formation becomes energetically favorable over an arrangement of Ising states in higher energy vertex configurations. Energy analysis suggests that while magnetostatic energy dominates the energetics, the small contribution from exchange energy determines whether nanoislands can exist in Ising or CST states. The nanoisland magnetic state changes the magnetostatics arising from both intra-island shape anisotropy and inter-island dipolar interaction. These results suggest the potential to create tunable nanoisland domain states, providing a new direction in the development of ASI systems with exotic phase transitions as well as novel nanomagnetic logic architectures.  Energetics of complex spin textures in LSMO artificial spin ice structures