Mechanisms of Skyrmion and Skyrmion Crystal Formation from the Conical Phase

Real-space topological magnetic structures such as skyrmions and merons are promising candidates for information storage and transport. However, the microscopic mechanisms that control their formation and evolution are still unclear. Here, using in situ Lorentz transmission electron microscopy, we demonstrate that skyrmion crystals (SkXs) can nucleate, grow, and evolve from the conical phase in the same ways that real nanocrystals form from vapors or solutions. More intriguingly, individual skyrmions can also “reproduce” by division in a mitosis-like process that allows them to annihilate SkX lattice imperfections, which is not available to crystals made of mass-conserving particles. Combined string method and micromagnetic calculations show that competition between repulsive and attractive interactions between skyrmions governs particle-like SkX growth, but nonconservative SkX growth appears to be defect mediated. Our results provide insights toward manipulating magnetic topological states by applying established crystal growth theory, adapted to account for the new process of skyrmion mitosis

Interfacial-hybridization-modified Ir Ferromagnetism and Electronic Structure in LaMnO3_3/SrIrO3_3 Superlattices

Artificially fabricated 3$d$/5$d$ superlattices (SLs) involve both strong electron correlation and spin-orbit coupling in one material by means of interfacial 3$d$-5$d$ coupling, whose mechanism remains mostly unexplored. In this work we investigated the mechanism of interfacial coupling in LaMnO$_3$/SrIrO$_3$ SLs by several spectroscopic approaches. Hard x-ray absorption, magnetic circular dichroism and photoemission spectra evidence the systematic change of the Ir ferromagnetism and the electronic structure with the change of the SL repetition period. First-principles calculations further reveal the mechanism of the SL-period dependence of the interfacial electronic structure and the local properties of the Ir moments, confirming that the formation of Ir-Mn molecular orbital is responsible for the interfacial coupling effects. The SL-period dependence of the ratio between spin and orbital components of the Ir magnetic moments can be attributed to the realignment of electron spin during the formation of the interfacial molecular orbital. Our results clarify the nature of interfacial coupling in this prototypical 3$d$/5$d$ SL system and the conclusion will shed light on the study of other strongly correlated and spin-orbit coupled oxide hetero-interfaces

Ceramics International Preface

close0

Thermoelectric thin films: Promising strategies and related mechanism on boosting energy conversion performance

Thermoelectrics can be capable of direct and reversible conversion between heat and electricity. Low dimensional thermoelectric materials, especially two dimensional (2D) thin films, have been considered as a breakthrough to decouple the correlations between electronic and thermal transport, contributing to the optimization of thermoelectric performance. During the past few decades, some effective strategies combined with physical concepts like quantum confinement effect, energy filtering effect, band structure tuning and interface engineering are introduced to design high performance thermoelectrics. Having a thorough understanding the underlying mechanisms is essential to develop thermoelectric materials. Here, our review summarizes the major strategies that can be utilized in thermoelectric thin films, including fabrication of superlattice structure, formation of two-dimensional electron gas (2DEG) system, orientation regulation, strain engineering and magnetic manipulation, from the aspects of deep mechanisms analyses, recent progress and prospects, inspiring significant improvement of thermoelectric properties

Photoelectrochemical Performance Observed in Mn-Doped BiFeO3 Heterostructured Thin Films

Pure BiFeO3 and heterostructured BiFeO3/BiFe0.95Mn0.05O3 (5% Mn-doped BiFeO3) thin films have been prepared by a chemical deposition method. The band structures and photosensitive properties of these films have been investigated elaborately. Pure BiFeO3 films showed stable and strong response to photo illumination (open circuit potential kept −0.18 V, short circuit photocurrent density was −0.023 mA·cm−2). By Mn doping, the energy band positions shifted, resulting in a smaller band gap of BiFe0.95Mn0.05O3 layer and an internal field being built in the BiFeO3/BiFe0.95Mn0.05O3 interface. BiFeO3/BiFe0.95Mn0.05O3 and BiFe0.95Mn0.05O3 thin films demonstrated poor photo activity compared with pure BiFeO3 films, which can be explained by the fact that Mn doping brought in a large amount of defects in the BiFe0.95Mn0.05O3 layers, causing higher carrier combination and correspondingly suppressing the photo response, and this negative influence was more considerable than the positive effects provided by the band modulation

Enhanced Thermoelectric Properties of Cu3SbSe3-Based Composites with Inclusion Phases

Cu3SbSe3-based composites have been prepared by self-propagating high-temperature synthesis (SHS) combined with spark plasma sintering (SPS) technology. Phase composition and microstructure analysis indicate that the obtained samples are mainly composed of Cu3SbSe3 phase and CuSbSe2/Cu2−xSe secondary phases. Our results show that the existence of Cu2−xSe phase can clearly enhance the electrical conductivity of the composites (~16 S/cm), which is 2.5 times higher than the pure phase. The thermal conductivity can remain at about 0.30 W·m−1·K−1 at 653 K. A maximum ZT (defined as ZT = S2σΤ/κ, where S, σ, Τ, κ are the Seebeck coefficient, electrical conductivity, absolute temperature and total thermal conductivity) of the sample SPS 633 can be 0.42 at 653 K, which is 60% higher than the previously reported values. Our results indicate that the composite structure is an effective method to enhance the performance of Cu3SbSe3

Dielectric films for high performance capacitive energy storage: multiscale engineering

Dielectric capacitors are fundamental components in electronic and electrical systems due to their high-rate charging/discharging character and ultrahigh power density. Film dielectrics possess larger breakdown strength and higher energy density...</p