Simple Models of Lateral Heterostructures

Physics of the Solid State - General analytical expressions for densities of states of a lateral heterostructure, formed by the contact of two square semi-infinite lattices with single-band and...     

Oxford Dictionary of Astronomy,by Ian Ridpath

Problems associated with long-range ordering phenomena in polytypic systems, such as SiC, are discussed and applied to the barium ferrite system, in which a very large number of crystallographically distinct compounds of general formula M,Y, have been reported. They are formed by regular coherent intergrowth of Ba Fe₁₂O₁₉ (‘phsee M’) with Ba₂Me₂Fe₁₂O₂₂ (‘phase Y’, with Me = Fe²+, Ni²+, etc.), and have c axes from below 10 nm to over 150 nm. Electron microscopy has been applied to these materials end conditions are described under which hges can be interpreted on an intuitive basis; ultra-high resolution lattice images of correctly oriented thin crystals show contrast which is a projection of the charge density. The positions of tunnels through the crystals, parallel to [1120], are clearly revealed in these images and allow one to distinguish between M and Y units.

It is thus shown that elthougb the crystallographic repeat units may be extremely long, extensive crystallographic domains of complex stacking sequences are built up with regularity, although occasional mistekes are found. Within a single, macroscopic crystal. however, the staoking pattern and ohemical composition may very at different points along the c axis, i.e. at different stages in crystal growth. The crystals have a domain structure and electron microscopy reveals domains with compositions and stacking sequences not hitherto found by X-ray methods.     

Magnetism of surfaces by spin polarized photoemission

Spin polarized photoemission is used as a method to study the magnetic peoperties of solid surfaces. Here we consider those systems where the spin polarization is believed to be conserved during the photoemission process. The surface sensitivity of the experiment will be therefore mainly determined by the relative magnitudes of the escape depth of the photoelectrons and of the magnetic coherence length. We analyze both the temperature and magnetic-field dependence of the degree of spin polarizationP of the electrons emitted from single crystals of magnetite, Fe₃O₄, and thin films (D=2–3000 Å) of Fe, Co and Ni. These data yield information on 1) the temperature dependence of the magnetization of the surface, 2) the relative sizes of and, 3) changes of the magnetic moment of atoms in the surface layers, and 4) the surface magnetic anisotropy. We show that this technique emerges as a novel tool to study magnetic systems with free surfaces and to test the predictions of recent calculations of the magnetic properties of surfaces. Emphasis is given to the fact that only relative changes ofP and not its absolute values are relevant for an analysis of the data.     

KKR-CPA-LDA计算方法对CuMnAl和CoMnAl以及CuCoMnAl合金的磁性研究

采用KKR-CPA-LDA方法研究了CuMnAl,CoMnAl和CuCoMnAl四元合金中磁性原子磁矩和Co-Mn间的交换作用.通过与实验结果对比,揭示了Mn的磁矩和Co的磁矩以及它们的相互作用随成分变化的规律.研究发现,在Cu₅₀Mn_25+xAl25-x合金中超过化学配比并占据Al位的Mn原子是反铁磁的,而且由于近邻环境的不同,其磁矩大于原有Mn原子的磁矩.在Co₅₀Mn_{25+< 关键词： KKR-CPA-LDA计算 Co-Mn间交换作用}     

Magnetism induced by capping of non-magnetic ZnO nanoparticles

Magnetism of 10 nm size capped nanoparticles, NPs, of non-magnetic ZnO is analysed in terms of the surface band since, as magnetic dichroism analysis has pointed out, impurity atoms bonded to the surface act as donor or acceptor of electrons that occupy the surface states. Due to the nanometric scale of the particles the kinetic energy spectrum of the surface states can be considered as discrete. Therefore, the magnetic polarisation cannot be easily induced by pumping electrons to energy levels above the Fermi energy. It is in the Fermi level itself, generally unfilled, that develops a spontaneous magnetic moment similarly to that induced by Hund rules in unfilled atomic orbitals. It is shown, however, that the total magnetic moment of the surface originated at the unfilled Fermi level can reach values as large as 10² or 10³ Bohr magnetons.     

Magnetism of nanowires driven by novel even-odd effects

The parity of the number of atoms in finite antiferromagnetic nanowires deposited on ferromagnets is shown to be a crucial quantity determining their magnetic ground state. Relating results of the full-potential Korringa-Kohn-Rostoker method for noncollinear magnetism from first principles to a Heisenberg model, we show that the magnetic structure changes dramatically across the entire nanowire if one single atom is added to it. Infinite and finite even-numbered nanochains exhibit always noncollinear magnetism, while odd-numbered wires lead under given conditions to a collinear ferrimagnetic ground state. This extremely nonlocal effect occurs only for nanosized wires.     

Magnetism of single-walled silicon carbide nanotubes doped by boron,nitrogen and oxygen

We calculated, using spin polarized density functional theory, the electronic properties of zigzag (10,0) and armchair (6,6) semiconductor silicon carbide nanotubes (SiCNTs) doped once at the time with boron, nitrogen, and oxygen. We have looked at the two possible scenarios where the guest atom X (B, N, O), replaces the silicon X_Si, or the carbon atom X_C, in the unit cell. We found that in the case of one atom B @ SiCNT replacing a carbon atom position annotated by B_C exhibits a magnetic moment of 1 μ_B/cell in both zigzag and armchair nanotubes. Also, B replacing Si, (B_Si), induce a magnetic moment of 0.46 μ_B/cell in the zigzag (10,0) but no magnetic moment in armchair (6,6). For N substitution; (N_C) and (N_Si) each case induce a magnetic moment of 1 μ_B/cell in armchair (6,6), while N_Si give rise to 0.75 μ_B/cell in zigzag (10,0) and no magnetic moment for N_C. In contrast the case of O_C and O_Si did not produce any net magnetic moment in both zigzag and armchair geometries.     

V,Cr,Mn掺杂MoS2磁性的第一性原理研究

基于第一性原理的自旋极化密度泛函理论分别研究了过渡金属V, Cr, Mn掺杂单层MoS₂的电子结构、 磁性和稳定性. 结果表明: V和Mn单掺杂均能产生一定的磁矩, 而磁矩主要集中在掺杂的过渡金属原子上, Cr单掺杂时体系不显示磁性. 进一步讨论双原子掺杂MoS₂ 体系中掺杂原子之间的磁耦合作用发现, Mn掺杂的体系在室温下显示出稳定的铁磁性, 而V掺杂则表现出非自旋极化基态. 形成能的计算表明Mn掺杂的MoS₂体系相对V和Cr 掺杂结构更稳定. 由于Mn掺杂的MoS₂ 不仅在室温下可以获得比较好的铁磁性而且其稳定性很高, 有望在自旋电子器件方面发挥重要的作用. 关键词： 2')" href="#">单层MoS₂ 掺杂 铁磁态 第一性原理     

Magnetism,optical,and thermoelectric response of CdFe_2O_4by using DFT scheme

Comparative analysis of electronic, magnetic, optical, and thermoelectric properties of CdFe_2O_4, calculated by employing PBEsol + mBJ has been done. The PBEsol reveals metallic nature, while TB-mBJ illustrates ferromagnetic semiconducting behavior. The reasons behind the origin of ferromagnetism are explored by observing the exchange, crystal field, and John–Teller energies. The optical nature is investigated by analyzing dielectric constants, refraction, absorption coefficient, reflectivity, and optical conductivity. Finally, thermoelectric properties are elaborated by describing the electrical and thermal conductivities, Seebeck coefficient, and power factor. The strong absorption for the visible energy and high power factor suggest CdFe_2O_4 as the potential candidate for renewable energy applications.     

Electricity and Magnetism,Volume 1: Third Edition,Electricity and Magnetism,Volume 2: Third Edition,by B.I. Bleaney and B. Bleaney

During the last decade the term ‘spin glass’ has become prominent in the literature on magnetism. It refers to magnetic alloys where the spins on the impurities become locked or frozen into random orientations below a characteristic temperature T ₀. In this article the properties of spin glasses are described with particular reference to the two archetypal examples AuFe and CuMn. Interest in spin glasses was mainly stimulated by some a.c. susceptibility measurements which showed sharp, cusp-like peaks, accurately defining T ₀ and suggesting that some type of phase transition was occurring. The Mossbauer effect and the anomalous Hall effect also showed clear features at T ₀ supporting this viewpoint. But measurements of the electrical resistivity and ‘specific heat’, here usually meaning the molar heat capacity, also the remanence, magnetic hysteresis and time-dependent effects observed in spin glasses were difficult to reconcile with a phase transition approach. This article discusses the results obtained from the very wide variety of experimental techniques which have been used to investigate spin glasses, and also deals with some of the important theoretical concepts which have arisen out of these studies. Then follows a short account of the many systems which have been found to exhibit spin glass behaviour and which suggest that it is a widespread magnetic state of matter. Lastly, an example is given which shows that some of the ideas of spin glasses are applicable to problems outside the sphere of magnetic alloys.     

Coupled-Channels Approach and Simple Models in the Theory of Exotic Atom Formation

Atomic collisions of slow negative particles X ^? (μ^?, $\bar p$ , etc.) are considered using coupled channels semiclassical approximation that takes into account 2- and 3-particle channels. Analytical expression for differential elastic cross section is proposed. Differential cross section reveals essential quantum interference effects. Inelastic $\bar p$ –Ne and $\bar p$ –Ar cross sections are considered using model potentials.     

The Oxford Handbook of Philosophy of Physics,edited by R. Batterman

There are three ways in which an expected symmetry may not hold exactly: first, if the basic laws do not respect the symmetry exactly; second, if the initial or boundary conditions do not obey the symmetry; and third, by a spontaneous breakdown, which can happen in two ways, here called SBS1 and SBS2, which will be defined and illustrated. Similar to them is the symmetry-breaking approximation, in which a symmetric system is approximated by an asymmetric formalism to make it easier to handle certain correlations.