Temperature driven macro-ferromagnetism in 'pinwheel' artificial spin ice*

Artificial spin ice are patterned structure of arranged magnetic elements such that their interactions produce correlations and competitions that can be used to generate non-trivial dynamics and complex magnetic orderings. In this work, we investigate thermodynamic properties of geometries which are simple but fundamental variants of the original square lattice. We shown how a simple rotation of the elements induces a drastic change in the dipolar energy.

We have used Monte Carlo simulations to understand thermal induced ordering processes in artificial spin ice and a curious emergent chiral symmetry breaking that appears in the new spin ice structures (specially at 45⁰). This new system has also shown to be a model for studying a classical counterpart to a quantum phase transition. Here we show how the classic antiferromagnetic spin ice array (0⁰) becomes ferromagnetic (45⁰) and by doing so flux closure vortex-like magnetisation patter emerge due to boundary effects (note that such structure is not seen when periodic boundary conditions (PBC) are considered).