Tunable Ground State in Heterostructured Artificial Spin Ice with Exchange Bias

We describe an artificial spin ice (ASI) composed of exchange biased heterostructured nanomagnetic elements with unidirectional anisotropy and compare it with a conventional ASI constituted by ferromagnets with uniaxial anisotropy (Ising spins). The introduction of a local exchange bias field, aligned along one of the sublattices of the square ASI, lifts the spin-reversal symmetry of the vertices. By varying the lattice constant of the square array, we control the ratio of exchange bias (EB) to dipolar field ( H EB / H dip ) and tune the ground state from an antiferromagnetic to a ferromagnetic configuration with an effective magnetic moment. The geometric frustration of dipolar interactions is moderated by a nonfrustrated local field, leading to a mesoscopic system with specific metastable states observed during the demagnetization process.