Figure 5: Exchange bias evolution for a superlattice with 7-ML-thick (111)-LNO layers.

Schematics of the field-cooling procedure: (a) at the FM ordering temperature, the LMO layers induce a moment in the interfacial Ni, which (b) subsequently stabilizes a magnetic defect (orange triangles) in the (¼,¼,¼) AF order. This configuration freezes in during field cooling and gives the starting point for the field measurements. (c) At low temperature, the anisotropy in LNO is large and the magnetic defect is frozen inside these layers. At negative field, both interfacial exchange energies J_S and J_I are frustrated, resulting in the existence of negative EB. As temperature increases, the anisotropy weakens and becomes smaller than the larger of the two interface exchanges (J_I). (d) In this intermediate-temperature case, a negative field reverses the Ni spins on one side of the LMO interface and annihilates the magnetic defect in LNO. This configuration is stabilized if J_S is the smallest energy scale, thus inducing a sign change of the exchange bias field. (e) At higher temperature, the anisotropy is negligible and all the energy terms are minimized when the LMO layers are AF-ordered.