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Enhanced interfacial ferromagnetism and exchange bias in (111)-oriented LaNiO3/CaMnO3 superlattices


Emergent properties of complex oxide interfaces are based on interface reconstruction that is driven by mismatch of electronic bands, valence states, interaction lengths, and even crystal symmetry of the interface. In particular, emergent ferromagnetism at the interface of two materials that do not exhibit ferro- or ferrimagnetism in the bulk has been stabilized as a result of competing exchange interactions. When LaNiO3 and CaMnO3, which are a paramagnetic metal and antiferromagnetic insulator in the bulk, respectively, are brought together, ferromagnetism emerges at the interface. Here we show that in (111)-oriented LaNiO3/CaMnO3 (LNO/CMO) superlattices, Ni2+-Mn4+ superexchange interactions due to polar mismatch at the LNO/CMO interfaces are responsible for the emergent ferromagnetism. Compared to (001)-oriented LNO/CMO superlattices, (111)-oriented LNO/CMO superlattices exhibit enhanced interfacial ferromagnetism with a TC>200 K, greater than the bulk antiferromagnetic transition temperature of CaMnO3 and a saturated magnetic moment enhanced by up to a factor of 3. Furthermore, we observe exchange bias in (111)-oriented superlattices. The strong exchange interactions along the (111) interface, manifest in the enhanced Tc and exchange bias, make this class of CMO-based materials with (111)-oriented interfaces good candidates for low-dimensional spin-polarized materials in spintronic applications.

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