Interfacial Ferromagnetism and Exchange Bias inCaRuO3/CaMnO3Superlattices

Abstract

We have found ferromagnetism in epitaxially grown superlattices of ${\mathrm{CaRuO}}_3/{\mathrm{CaMnO}}_3$ that arises in one unit cell at the interface. Scanning transmission electron microscopy and electron energy loss spectroscopy indicate that the difference in magnitude of the Mn valence states between the center of the ${\mathrm{CaMnO}}_3$ layer and the interface region is consistent with double exchange interaction among the Mn ions at the interface. Polarized neutron reflectivity and the ${\mathrm{CaMnO}}_3$ thickness dependence of the exchange bias field together indicate that the interfacial ferromagnetism is only limited to one unit cell of ${\mathrm{CaMnO}}_3$ at each interface. The interfacial moment alternates between the $1{\mu }_B/\mathrm{\text{interface}}$ Mn ion for even ${\mathrm{CaMnO}}_3$ layers and the $0.5{\mu }_B/\mathrm{\text{interface}}$ Mn ion for odd ${\mathrm{CaMnO}}_3$ layers. This modulation, combined with the exchange bias, suggests the presence of a modulating interlayer coupling between neighboring ferromagnetic interfaces via the antiferromagnetic ${\mathrm{CaMnO}}_3$ layers.