Spin State Control using Oxide Interfaces in LaCoO$_{\mathbf{3}}$\textbf{-based Heterostructures}

The flexibility of the spin degree of freedom of the Co 3d orbitals in LaCoO$_{3}$ suggests that they can be changed through careful design of oxide heterostructures. Interfacial coupling and dimensional confinement can be used to control the magnetic exchange, crystal fields, and Hund's coupling, through orbital and charge reconstructions. These parameters control the balance between multiple spin configurations, thereby modifying the magnetic ordering of LaCoO$_{3}$. We study (LaCoO$_{3})_{m}$/(LaTiO$_{3})_{2}$ heterostructures grown by molecular beam epitaxy, which allow interfacial charge transfer from Ti to Co, in addition to structural and dimensional constraints. The electronic polarization at the interface and consequent structural distortions suppress the ferromagnetism in the LaCoO$_{3}$ layers. This effect extends well beyond the interface, with ferromagnetic order absent up to LaCoO$_{3}$ layer thickness of m$=$10. We compare the properties of the LaCoO$_{3}$/LaTiO$_{3}$ heterostructures with LaCoO$_{3}$/SrTiO$_{3}$, to untangle how charge transfer and structural modifications control the spin and magnetic configuration in cobaltates.