Co valence transformation in isopolarLaCoO3/LaTiO3perovskite heterostructures via interfacial engineering

Abstract

PhySH: Complex oxides; transition metal oxides; X-ray absorption; X-ray magnetic circular dichroism; thin films; scanning transmission electron microscopy. Abstract We report charge-transfer up to a single electron per interfacial unit cell across non-polar heterointerfaces from the Mott insulator LaTiO 3 to the charge transfer insulator LaCoO 3 . In high-quality bi-and tri-layer systems grown using pulsed laser deposition, soft X-ray absorption, dichroism and STEM-EELS are used to probe the cobalt 3d-electron count and provide an element-specific investigation of the magnetic properties. The experiments prove a deterministically-tunable charge transfer process acting in the LaCoO 3 within three unit cells of the heterointerface, able to generate full conversion to 3d 7 divalent Co, which displays a paramagnetic ground state. The number of LaTiO 3 |LaCoO 3 interfaces, the thickness of an additional 'break' layer between the LaTiO 3 and LaCoO 3 , and the LaCoO 3 film thickness itself in tri-layers provide a trio of sensitive control knobs for the charge transfer process, illustrating the efficacy of O2p-band alignment as a guiding principle for property design in complex oxide heterointerfaces.

Probing surfaces and interfaces in complex oxide films via in situ X-ray photoelectron spectroscopy

“…Similar measurements for a LaNiO 3 /LaMnO 3 heterostructure indicated electron transfer from Mn to Ni at the interface [4]. A combined XPS and XAS study of LaCoO 3 /LaTiO 3 heterostructures also indicated charge transfer to produce Co 2+ and Ti 4+ valences at the interface [111]. Charge transfer in SrMnO 3 /SrIrO 3 to produce Mn 3+ and Ir 5+ [46,47] and LaMnO 3 /SrIrO 3 to produce Mn 2+ and Ir 5 + [48] heterostructures has also been demonstrated.…”

Probing surfaces and interfaces in complex oxide films via in situ X-ray photoelectron spectroscopy

“…Similar measurements for a LaNiO 3 /LaMnO 3 heterostructure indicated electron transfer from Mn to Ni at the interface [4]. A combined XPS and XAS study of LaCoO 3 /LaTiO 3 heterostructures also indicated charge transfer to produce Co 2+ and Ti 4+ valences at the interface [111]. Charge transfer in SrMnO 3 /SrIrO 3 to produce Mn 3+ and Ir 5+ [46,47] and LaMnO 3 /SrIrO 3 to produce Mn 2+ and Ir 5 + [48] heterostructures has also been demonstrated.…”

Charge‐Transfer‐Induced Multivalent States with Resultant Emergent Magnetism in Transition‐Metal Oxide Heterostructures

“…However, no dichroism is found from Co 2+ , implying Co 2+ ions do not contribute to the ferromagnetism. A spin block between these multivalent Co ions also prohibits the hopping process and suppresses the conduction, [ 21 ] as experimentally proved in Figure 1g.…”

“…For example, the origin of an emergent ferromagnetism has been vigorously investigated but remains controversial in the LaMnO 3 /SrTiO 3 (LMO/STO) and LaCoO 3 / SrTiO 3 (LCO/STO) heterostructures. [16][17][18][19][20][21] Nowadays, it shows that charge transfer-induced multivalent states of Mn have been unambiguously evidenced to induce novel ferromagnetism. [22] Similarly, electronic, spin, and orbital similarities among the 3d metals may allow this charge transfer-induced multivalence to be generalized for other TMO heterostructures, while the answer still remains elusive.…”