Magnetic coupling through lanthanum nickelate in non-metallic (111) LaMnO$_{\mathrm{3}}$/LaNiO$_{\mathrm{3}}$ superlattices

Perovskite nickelates (RNiO$_{\mathrm{3}}$, R$=$rare earth), with the exception of LaNiO$_{\mathrm{3}}$, display a bandwidth-controlled metal insulator transition (MIT) and antiferromagnetic order in the low temperature phase. Tuning of the MI and N\'{e}el transitions is efficiently achieved in nickelate thin films over a wide temperature range, and even LaNiO$_{\mathrm{3}}$ films undergo a MIT as the thickness is decreased. In this reduced dimensionality regime of LaNiO$_{\mathrm{3}}$, we will also report how interface engineering can be used not only to induce a new magnetic phase in this otherwise non-magnetic material but also to generate rich and complex magnetic behavior in (111)-oriented LaNiO$_{\mathrm{3}}$/LaMnO$_{\mathrm{3}}$ heterostructures. For 7-monolayer-thick LaNiO$_{\mathrm{3}}$/LaMnO$_{\mathrm{3}}$ superlattices, the emergence of negative and positive exchange bias is observed at low temperature before the stabilization of an antiferromagnetically coupled state between the LaMnO$_{\mathrm{3}}$ layers above the blocking temperature. This behavior is explained by the onset of an antiferromagnetic spiral of (1/4, 1/4 ,1/4) wave vector in the ultrathin LaNiO$_{\mathrm{3}}$ layer, akin to that of the other bulk insulating nickelates. Influence of the degree of intermixing at the monolayer scale on the interface-driven properties will also be discussed.