  To investigate the relationship between the charge redistribution and
ferromagnetism at the heterointerface between perovskite transition-metal
oxides LaNiO$_3$ (LNO) and LaMnO$_3$ (LMO), we performed x-ray absorption
spectroscopy and x-ray magnetic circular dichroism (XMCD) measurements. In the
LNO/LMO heterostructures with asymmetric charge redistribution, the electrons
donated from Mn to Ni ions are confined within one monolayer (ML) of LNO at the
interface, whereas holes are distributed over 3-4 ML on the LMO side. A
detailed analysis of the Ni-$L_{2,3}$ and Mn-$L_{2,3}$ XMCD spectra reveals
that Ni magnetization is induced only by the Ni$^{2+}$ ions in the 1 ML LNO
adjacent to the interface, while the magnetization of Mn ions is increased in
the 3-4 ML LMO of the interfacial region. The characteristic length scale of
the emergent (increased) interfacial ferromagnetism of the LNO (LMO) layers is
in good agreement with that of the charge distribution across the interface,
indicating a close relationship between the charge redistribution due to the
interfacial charge transfer and the ferromagnetism of the LNO/LMO interface.
Furthermore, the XMCD spectra clearly demonstrate that the vectors of induced
magnetization of both ions are aligned ferromagnetically, suggesting that the
delicate balance between the exchange interactions occurring inside each layer
and across the interface may induce the canted ferromagnetism of Ni$^{2+}$
ions, resulting in weak magnetization in the 1 ML LNO adjacent to the
interface.
