Formation and tuning of 2D electron gas in perovskite heterostructures

Oxide interfaces provide very intriguing phenomena, in particular a 2D electron gas (2DEG) emerging between robustly insulating perovskites. The 2DEG was detected in 2004 beneath polar LaAlO3 (LAO) epitaxially grown on TiO2-terminated SrTiO3 (001) (STO). Herein, recent first-principles studies of 2DEGs are reviewed. Using a Green function method, the family of the polar/nonpolar (001) interfaces: LAO/STO, LaFeO3/STO, and STO/KTaO3 is computed. In the context of 2DEG, one of two insulating perovskites, at least, must be polar. The effect of a polar/polar interface is modeled for LAO/KTaO3(001) and also for the (110) and (111) interfaces of LAO/STO. Starting from the defectless superlattice with its two differently terminated interfaces, we demonstrate that the 2DEG and 2D hole gas appear there, respectively, due to the presence of excessive electrons or holes. 2DEG is evaluated by its layer-resolved density profile along [001], as well as the Fermi surface cross sections and effective masses, which are directly related to the transport properties. The effects of intermixed cations, their vacancies, and oxygen vacancies at each interface of LAO/STO are calculated. Finally, we show how to tune reversibly the 2DEG by changing the electronic balance at the LAO surface that mimics the effect of ionic liquid gating

Nonlinear Decay of Quantum Confined Magnons in Itinerant Ferromagnets

Quantum confinement leads to the emergence of several magnon modes in ultrathin layered magnetic structures. We probe the lifetime of these quantum confined modes in a model system composed of three atomic layers of Co grown on different surfaces. We demonstrate that the quantum confined magnons exhibit nonlinear decay rates, which strongly depend on the mode number, in sharp contrast to what is assumed in the classical dynamics. Combining the experimental results with those of linear-response density functional calculations we provide a quantitative explanation for this nonlinear damping effect. The results provide new insights into the decay mechanism of spin excitations in ultrathin films and multilayers and pave the way for tuning the dynamical properties of such structures

Electronic and magnetic properties of BaFeO₃ on the Pt(111) surface in a quasicrystalline approximant structure

Perovskite‐like ABO3 oxides A = (Ca, Sr, Ba) and B = (Ti, Mn, Fe, Co, Ni) show a large variety of structures and physical properties. Among them is BaTiO3 (BTO), one of the most investigated and used perovskites. In a BTO film on Pt(111), the first oxide quasicrystal was discovered. Herein, by means of first‐principle methods, the cubic and hexagonal phases of bulk BaFeO3 (BFO) are investigated. Both phases show ferromagnetic order. Monolayers and double layers of BFO are studied on a Pt(111) surface. The double‐layer configuration of the cubic and hexagonal phases is structurally inequivalent but both double‐layer films show antiferromagnetic order. In analogy to the BTO quasicrystal approximant structure on Pt(111), a corresponding BFO structure is investigated. The Fe atoms are surrounded by three oxygen atoms and the resulting FeO3 units are separated by barium atoms with the total stoichiometry Ba5Fe4O12

The Problem Analysis of Existing FSES of Higher Education for the Enlarged Group of Specialties"the Service and Tourism"

The article presents the results of aspect analysis of the current federal state educational standards of higher education for the enlarged group of specialties"Service and tourism". There are analyzed the conformity of educational standards of higher education to the requirements of employers, the requirements for development results, to the structure and terms of realization of educational programs of undergraduate/graduate. The authors outline the key problems for each aspect, also identifythe relevant disadvantages.This analysis will help us to find solutions to the identified key problems and make possible the designing/updating of education standards

Exchange interaction and its tuning in magnetic binary chalcogenides

Using a first-principles Green's function approach we study magnetic properties of the magnetic binary chalcogenides Bi2Te3, Bi2Se3, and Sb2Te3. The magnetic coupling between transition-metal impurities is long-range, extends beyond a quintuple layer, and decreases with increasing number of d electrons per 3d atom. We find two main mechanisms for the magnetic interaction in these materials: the indirect exchange interaction mediated by free carriers and the indirect interaction between magnetic moments via chalcogen atoms. The calculated Curie temperatures of these systems are in good agreement with available experimental data. Our results provide deep insight into magnetic interactions in magnetic binary chalcogenides and open a way to design new materials for promising applications

Thickness-dependent Ru exchange spring at La_0.7Sr_0.3MnO₃–SrRuO₃ interface

The conducting oxide ferromagnets SrRuO3 (SRO) and LaSr0.3MnO3 (LSMO) form a Ru exchange spring at a coherent low‐interdiffusion interface grown on TiO2‐terminated SrTiO3(STO)(001) substrates as SRO(d)/LSMO/STO(001) bilayers. Field‐ and temperature‐dependent magnetization data with systematically varied thickness d of SRO from 7 to 18 unit cells (uc) indicate a thickness of 10–14 uc of the exchange spring which governs magnetic switching and causes thickness‐dependent field‐cooling effects. Mn L3 edge X‐ray magnetic circular dichroism (XMCD) data reveal the dominating in‐plane orientation of interfacial spins. In low magnetic fields, noncoplanar, topologically nontrivial spin textures arise and can be switched, driven by the Zeeman energy of the LSMO layer

Exchange interaction and its tuning in magnetic binary chalcogenides

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).-- et al.Using a first-principles Green's function approach we study magnetic properties of the magnetic binary tetradymite chalcogenides Bi2Se3, Bi2Te3, and Sb2Te3. The magnetic coupling between transition-metal impurities is long range, extends beyond a quintuple layer, and decreases with increasing number of d electrons per 3d atom. We find two main mechanisms for the magnetic interaction in these materials: the indirect exchange interaction mediated by free carriers and the indirect interaction between magnetic moments via chalcogen atoms. The calculated Curie temperatures of these systems are in good agreement with available experimental data. Our results provide deep insight into exchange interactions in magnetic binary tetradymite chalcogenides and open a way to design new materials for promising applications.We acknowledge support by the Tomsk State University Competitiveness Improvement Program and the Deutsche Forschungsgemeinschaft (Priority Program SPP 1666 “Topological Insulators”).Peer Reviewe