Interfacial Ferromagnetism and Exchange Bias inCaRuO3/CaMnO3Superlattices

Abstract

We have found ferromagnetism in epitaxially grown superlattices of CaRuO(3)/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 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 CaMnO(3) thickness dependence of the exchange bias field together indicate that the interfacial ferromagnetism is only limited to one unit cell of CaMnO(3) at each interface. The interfacial moment alternates between the 1 μ(B)/interface Mn ion for even CaMnO(3) layers and the 0.5 μ(B)/interface Mn ion for odd 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 CaMnO(3) layers.

Interface-induced phenomena in magnetism

“…At oxide interfaces, charge transfer can be driven by a difference in chemical potential or by screening of local dipoles. Charge transfer can alter the B -site valence states near the interface, enabling magnetic order that is distinct from either constituent, for instance leading to ferromagnetism confined to the interface between two insulating antiferromagnets [Salvador et al ., 1999; Lin et al ., 2006; Santos et al ., 2011] or ferromagnetism from a paramagnetic metal and antiferromagnetic insulator [Takahashi et al ., 2001; Nanda et al ., 2007; Freeland et al ., 2010; He et al ., 2012]. The spatial extent of the interfacial magnetism closely matches that of the charge transfer length scale, which is generally quite short, around 0.4 nm to 2 nm [Santos et al ., 2011; Grutter et al ., 2013; Hoffman et al ., 2013], owing to both the large dielectric constant and significant carrier concentration (charge density) that complex oxides often support [Ahn et al ., 2006].…”

Positive exchange-bias and giant vertical hysteretic shift in La0.3Sr0.7FeO3/SrRuO3 bilayers

“…Observation of EB in the disordered-ordered magnetic interfaces, i.e. , in paramagnetic (PM) LaNiO 3 and FM LaMnO 3 superlattice and the PM CaRuO 3 and AFM CaMnO 3 superlattices are clearly the recent important discoveries in this area1213. More recently, strain engineered unexpected EB with the emergence of a self assembled spin glass like phase of LaSrMnO 4 at the film/substrate interface was reported for (La,Sr)MnO 3 single thin-films17.…”

“…Overall the progress in EB has been two-fold. First, the EB has been addressed in unconventional heterostructures/bilayers with FM-PM, AFM-PM and collinear-noncollinear magnetic heterostructures7121316. This has challenged our present understanding of EB which is generally observed in conventional FM-AFM heterostructures1415.…”

Interfacial magnetic coupling in ultrathin all-manganite La0.7Sr0.3MnO3-TbMnO3 superlattices

“…[7][8][9][10][11] In a flurry of recent studies, ultrathin manganite films were incorporated in epitaxial heterostructures as a result of expectation of emergent physics such as tailored interfacial magnetic coupling and geometrically confined doping in such artificial lowdimensional systems. [12][13][14][15] Epitaxial superlattices (SLs) of complex oxides give access to fascinating physical phenomena as a result of magnetic frustration, charge transfer, and orbital reconstruction across interfaces. [16][17][18][19][20][21][22] In particular, exchange bias, as a prototypical interfacial magnetic interaction between different spin orders, was reported in some manganite-based heterostructures and SLs.…”