Emergent and robust ferromagnetic-insulating state in highly strained ferroelastic LaCoO3 thin films

Abstract

Transition metal oxides are promising candidates for the next generation of spintronic devices due to their fascinating properties that can be effectively engineered by strain, defects, and microstructure. An excellent example can be found in ferroelastic LaCoO3 with paramagnetism in bulk. In contrast, unexpected ferromagnetism is observed in tensile-strained LaCoO3 films, however, its origin remains controversial. Here we simultaneously reveal the formation of ordered oxygen vacancies and previously unreported long-range suppression of CoO6 octahedral rotations throughout LaCoO3 films. Supported by density functional theory calculations, we find that the strong modification of Co 3d-O 2p hybridization associated with the increase of both Co-O-Co bond angle and Co-O bond length weakens the crystal-field splitting and facilitates an ordered high-spin state of Co ions, inducing an emergent ferromagnetic-insulating state. Our work provides unique insights into underlying mechanisms driving the ferromagnetic-insulating state in tensile-strained ferroelastic LaCoO3 films while suggesting potential applications toward low-power spintronic devices.

A new pathway to correlate the octahedral tilt coupling and spin-orbit reconstruction at oxide interfaces

“…38 Additionally, the suppression of CoO6 octahedral rotations needs to be considered for the modification of eg orbital ordering configuration, leading to a spin-state transition to a ferromagnetic state. 39 Through our AC-STEM data (Fig. 2g), we observe the suppression of CoO6 octahedral rotations, as measured using the OOOproj angle, thereby manipulating Co orbital occupancy, Co-O bond length and Co-O-Co bond angle, ultimately weakening crystal-field splitting and promoting an ordered high-spin state of Co ions.…”

Radiation-Hardened and Flexible Pb(Zr0.53Ti0.47)O3 Piezoelectric Sensor for Structural Health Monitoring

“…Due to the superior radiation tolerance, perovskite oxide films, − especially lead-based series films, such as PbTiO 3 , Pb­(Zr 1– x Ti x )­O 3 , and 0.7Pb­(Mg 1/3 Nb 2/3 )­O 3 -0.3PbTiO 3 , are widely used as piezoelectric sensors, field effect transistors, and ferroelectric random access memories in harsh environments. − As one of the applications of lead-based materials, Lamb-wave-based structural health monitoring (SHM) systems rely on Pb­(Zr 1– x Ti x )­O 3 piezoelectric ceramics to excite and receive Lamb-wave response signals before and after damage occurs, thereby detecting damage and ensuring the safety of aerospace vehicles. − However, the rigid and fixed dimensions of Pb­(Zr 1– x Ti x )­O 3 ceramics hinder their application in damage monitoring on complex curved structures. And a heavy burden is brought to the aerospace vehicle by the weight of the Pb­(Zr 1– x Ti x )­O 3 ceramic network.…”

In-Situ Atomic-Scale Observation of Brownmillerite to Ruddlesden–Popper Phase Transition Tuned by Epitaxial Strain in Cobaltites

“…Especially for perovskite oxides, transitions among pristine ABO3, generalized Grenier (ABO2.67), brownmillerite (BM, ABO2.5), Ruddlesden-Popper (RP, A𝑛+1B𝑛O3𝑛+1), and infinite-layer (ABO2) phases provide platforms for superconductivity, [1,2] ferromagnetism, [3,4] and fast ionic conductivity. [5,6] The topotactic transition from ABO3 to BM phase, where the dedicatedly modulated oxygen vacancy ordering is strongly coupled with to the charge-orbital-spin configuration, has aroused wide research attentions to related structure-property relationship [7,8] and transition mechanisms. [9][10][11][12] However, further reduction beyond BM phases has not been fully understood.…”