Xiaofang Zhai

Metal-Insulator Transition and Its Relation to Magnetic Structure in (LaMnO3)2n/(SrMnO3)n Superlattices

Superlattices of (LaMnO3){2n}/(SrMnO3){n} (1<or=n<or=5), composed of the gapped insulators LaMnO3 and SrMnO3, undergo a metal-insulator transition as a function of n, being metallic for n<or=2 and insulating for n>or=3. Measurements of transport, magnetization, and polarized neutron reflectivity reveal that the ferromagnetism is relatively uniform in the metallic state, and is strongly modulated in the insulating state, being high in LaMnO3 and suppressed in SrMnO3. The modulation is consistent with a Mott transition driven by the proximity between the (LaMnO3)/(SrMnO3) interfaces. The insulating state for n>or=3 obeys variable range hopping at low temperatures. We suggest that this is due to states at the Fermi level that emerge at the (LaMnO3)/(SrMnO3) interfaces and are localized by disorder.

Enhanced ordering temperatures in antiferromagnetic manganite superlattices

The disorder inherent to doping by cation substitution in the complex oxides can have profound effects on collective-ordered states. Here, we demonstrate that cation-site ordering achieved through digital-synthesis techniques can dramatically enhance the antiferromagnetic ordering temperatures of manganite films. Cation-ordered (LaMnO3)m/(SrMnO3)2m superlattices show Néel temperatures (TN) that are the highest of any La(1-x)Sr(x)MnO3 compound, approximately 70 K greater than compositionally equivalent randomly doped La(1/3)Sr(2/3)MnO3. The antiferromagnetic order is A-type, consisting of in-plane double-exchange-mediated ferromagnetic sheets coupled antiferromagnetically along the out-of-plane direction. Through synchrotron X-ray scattering, we have discovered an in-plane structural modulation that reduces the charge itinerancy and hence the ordering temperature within the ferromagnetic sheets, thereby limiting TN. This modulation is mitigated and driven to long wavelengths by cation ordering, enabling the higher TN values of the superlattices. These results provide insight into how cation-site ordering can enhance cooperative behaviour in oxides through subtle structural phenomena.

Probing Interfacial Electronic Structures in Atomic Layer LaMnO3 and SrTiO3 Superlattices

The interfacial electronic structure characterization of a m x (LaMnO{sub 3})/n x (SrTiO{sub 3}) superlattice based on scanning transmission electron microscopy and electron energy loss spectroscopy. Evidence of interfacial band alignment and electron transfer are presented based on the observation of O K edge of individual transition metal and oxygen atomic columns. Electron probe aberration correction was essential for the high spatial resolution mapping of interfacial electronic states.

Nanoscale suppression of magnetization at atomically assembled manganite interfaces: XMCD and XRMS measurements

(LSMO)/SrTiO (STO) and a modified LSMO/LaMnO (LMO)/STO interface. Us-ing the technique of X-ray resonant magnetic scattering (XRMS), we can probe the interfaces ofcomplicated layered structures and quantitatively model depth-dependent magnetic profiles as afunction of distance from the interface. Comparisons of the average electronic and magnetic proper-ties at the interface are made independently using X-ray absorption spectroscopy (XAS) and X-raymagnetic circular dichroism (XMCD). The XAS and the XMCD demonstrate that the electronicand magnetic structure of the LMO layer at the modified interface is qualitatively equivalent tothe underlying LSMO film. From the temperature dependence of the XMCD, it is found that thenear surface magnetization for both interfaces falls off faster than the bulk. For all temperaturesin the range of 50K - 300K, the magnetic profiles for both systems always show a ferromagneticcomponent at the interface with a significantly suppressed magnetization that evolves to the bulkvalue over a length scale of ∼1.6 - 2.4 nm. The LSMO/LMO/STO interface shows a larger ferro-magnetic (FM) moment than the LSMO/STO interface, however the difference is only substantialat low temperature.I. INTRODUCTION

Electronic Reconstruction at SrMnO3-LaMnO3 Superlattice Interfaces

We use resonant soft-x-ray scattering (RSXS) to study the electronic reconstruction at the interface between the Mott insulator LaMnO3 and the band insulator SrMnO3. Superlattices of these two insulators were shown previously to have both ferromagnetism and metallic tendencies [Koida, Phys. Rev. B 66, 144418 (2002)10.1103/PhysRevB.66.144418]. By studying a judiciously chosen superlattice reflection, we show that the interface density of states exhibits a pronounced peak at the Fermi level, similar to that predicted in related titanate superlattices by Okamoto et al. [Phys. Rev. B 70, 241104(R) (2004)10.1103/PhysRevB.70.241104]. The intensity of this peak correlates with the conductivity and magnetization, suggesting it is the driver of metallic behavior. Our study demonstrates a general strategy for using RSXS to probe the electronic properties of heterostructure interfaces.

Magnetically asymmetric interfaces in a LaMnO 3 / SrMnO 3 superlattice due to structural asymmetries

Polarized neutron reflectivity measurements of a ferromagnetic

Suppressed magnetization at the surfaces and interfaces of ferromagnetic metallic manganites

{[{({text{LaMnO}}_{3})}_{11.8}/{({text{SrMnO}}_{3})}_{4.4}]}_{6}

Signatures of enhanced ordering temperatures in digital superlattices of (LaMnO3)m∕(SrMnO3)2m

superlattice reveal a modulated magnetic structure with an enhanced magnetization at the interfaces where

New Optical Absorption Bands in Atomic‐Layer Superlattices

{text{LaMnO}}_{3}

Magnetic properties of the (LaMnO3)N/(SrTiO3)N atomic layer superlattices

was deposited on