Delta Doping of Ferromagnetism in Antiferromagnetic Manganite Superlattices

TL;DR

This study shows that delta-doping in antiferromagnetic manganite superlattices induces localized ferromagnetism without disorder, revealing a fundamental length scale for charge transfer and magnetic modulation.

Contribution

It introduces a novel delta-doping technique to create confined ferromagnetism in AF manganites, confirming the canted AF state predicted by de Gennes.

Findings

Localized ferromagnetism induced by delta-doping

Observation of canted antiferromagnetic state

Identification of a charge transfer length scale

Abstract

We demonstrate that delta-doping can be used to create a dimensionally confined region of metallic ferromagnetism in an antiferromagnetic (AF) manganite host, without introducing any explicit disorder due to dopants or frustration of spins. Delta-doped carriers are inserted into a manganite superlattice (SL) by a digital-synthesis technique. Theoretical consideration of these additional carriers show that they cause a local enhancement of ferromagnetic (F) double-exchange with respect to AF superexchange, resulting in local canting of the AF spins. This leads to a highly modulated magnetization, as measured by polarized neutron reflectometry. The spatial modulation of the canting is related to the spreading of charge from the doped layer, and establishes a fundamental length scale for charge transfer, transformation of orbital occupancy and magnetic order in these manganites. Furthermore, we confirm the existence of the canted, AF state as was predicted by de Gennes [P.-G. de Gennes, Phys. Rev. 118, 141 (1960)], but had remained elusive.