Orbital Polarization and Magnetization for Independent Particles in Disordered Media

Formulas for the contribution of the conduction electrons to the polarization and magnetization are derived for disordered systems and within a one-particle framework. These results generalize known formulas for Bloch electrons and the presented proofs considerably simplify and strengthen prior justifications. The new formulas show that orbital polarization and magnetization are of geometric nature. This leads to quantization for a periodically driven Piezo effect as well as the derivative of the magnetization w.r.t. the chemical potential. It is also shown how the latter is connected to boundary currents in Chern insulators. The main technical tools in the proofs are an adaption of Nenciu’s super-adiabatic theory to C*-dynamical systems and Bellissard’s Ito derivatives w.r.t. the magnetic field.     

Weak Ferromagnetism and Field-Induced Spin Reorientation in K2V3O8

Magnetization and neutron diffraction studies of the 2D S = 1/2 antiferromagnet, K2V3O8, indicate an ordered state exhibiting weak ferromagnetism and field-induced spin reorientations. Of particular interest is the behavior in a basal plane magnetic field where a unique spin reorientation is observed in which the spins rotate from the easy c axis to the basal plane while remaining normal to the applied field. The experimental observations are well described by a two spin exchange model incorporating Heisenberg and Dzyaloshinskii-Moriya interactions with an additional c-axis anisotropy.     

Single-Ion Mechanism of Weak Ferromagnetism and a Spin-Flop Transition in One- and Two-Position Antiferromagnets

Nuclear resonance reflectivity from a [Dy₁₉Gd₁₉] × 20 superlattice has been measured utilizing the 25.652 keV nuclear level of ¹⁶¹Dy. The measured time spectra of nuclear resonance reflectivity make it possible to reveal the variation of the hyperfine magnetic field B_hf on dysprosium nuclei in the temperature range of 4–110 K and to determine the relaxation time of the hyperfine field, using the decay speed-up of the excited state of ¹⁶¹Dy nuclei.     

Controllable Spin Polarization of Charge Current by Rashba Spin Orbital Coupling

We report a theoretic study on modulating the spin polarization of charge current in a mesoscopic fourterminal device of cross structure by using the inverse spin hall effect. The scattering region of device is a two-dimensional electron gas （2DEG） with Rashba spin orbital interaction （RSOI）, one of lead is ferromagnetic metal and other three leads are spin-degenerate normal metals. By using Landauer-Biittiker formalism, we found that when a longitudinal charge current flows through 2DEG scattering region from FM lead by external bias, the transverse current can be either a pure spin current or full-polarized charge current due to the combined effect of spin hall effect and its inverse process, and the polarization of this transverse current can be easily controlled by several device parameters such as the Fermi energy, ferromagnetic magnetization, and the RSOI constant. Our method may pave a new way to control the spin polarization of a charge current.     

Controllable Spin Polarization of Charge Current by Rashba Spin Orbital Coupling

We report a theoretic study on modulating the spin polarization of charge current in a mesoscopic four-terminal device of cross structure by using the inverse spin hall effect. The scattering region of device is a two-dimensional electron gas (2DEG) with Rashba spin orbital interaction (RSOI), one of lead is ferromagnetic metal and other three leads are spin-degenerate normal metals. By using Landauer-Büttiker formalism, we found that when alongitudinal charge current flows through 2DEG scattering region from FM lead by external bias, the transverse current can be either a pure spin current or full-polarized charge current due to the combined effect of spin hall effect and its inverse process, and the polarization of this transverse current can be easily controlled by several device parameters such as the Fermi energy, ferromagnetic magnetization, and the RSOI constant. Our method may pave a new way to control the spin polarization of a charge current.     

Role of Light Polarization in the Optothermal Effect

It is shown that the highest optothermal effect in low-intensity irradiation is attained on chromophores of stationary orientation exposed to irradiation by a linearly polarized light. For chromophores with stochastization of orientation between the events of light absorption, the magnitude of the optothermal effect is independent of polarization and is three times lower than in stationary orientation. In anisotropic media, an optimally oriented linearly polarized light is more efficient.     

Splitting Single-Photon Polarization State with Weak Cross—Kerr Nonlinearity

We propose a three-party scheme for quantum information splitting (QIS) of an arbitrary single-photon polarization state based on weak cross-Kerr nonlinearity combined with linear optics elements such as polarization beam splitters (PBSs) and half wave plates (HWPs). The scheme is generalized to the arbitrary-party case. With the help of quantum nondemolition (QND) measurements, our schemes can be accomplished in an almost deterministic way. The two schemes are feasible with the current technology.     

Ferromagnetism in γ-iron

F.c.c. γ-Fe(111)-films, prepared by epitaxial growth in UHV on Cu(111), are ferromagnetic. The spontaneous magnetization was determined as 0.58 ± 0.13 μ_B/atom. This is independent of film thickness (up to 80 Å) and applies both for island-films and for layer-grown films. The Curie-temperature for bulk material was estimated to T_c(∞) = 900 ± 300 K. The apparent contradiction to antiferromagnetism in γ-Fe-precipitates is explained by different lattice parameters.     

Ferromagnetism in amorphous MgO

Abstract

We report, for the first time, the atomic structure of amorphous MgO based on ab initio molecular dynamics simulations. We find that its main building blocks are four-fold and five-fold coordinated configurations, similar to those formed in the liquid state. Its average coordination is estimated to be about 4.36. The amorphous form having a perfect stoichiometry has a band gap energy of 2.4 eV. On the other hand, Mg vacancies induce an insulator to metal transition and ferromagnetism in amorphous MgO whilst O vacancies do not cause such a transition, implying that the magnetism in amorphous MgO is related to the non-stoichiometry and Mg vacancies. With the application of pressure, the stoichiometric and non-stoichiometric (Mg vacancies) models undergo a phase transformation into a rocksalt state, suggesting that the electronic structure of the initial configurations has no influence on the resulting high-pressure phase in amorphous MgO.     

Ferromagnetism in Mn-doped GaN nanowires

Using density functional theory we show that the magnetic coupling of Mn atoms in the nanowires, unlike that in the thin film, is ferromagnetic. This ferromagnetic coupling, brought about due to the confinement of electrons in the radial direction and the curvature of the Mn-doped GaN nanowires' surface, is mediated by N as is evidenced from the overlap between Mn 3d and N 2p states. Calculations of the anisotropic energy further show that the magnetic moment orients preferably along the [1010] direction while the wire axis points along the [0001] direction.     

Ferromagnetism in the Hubbard model

Whether spin-independent Coulomb interaction can be the origin of a realistic ferromagnetism in an itinerant electron system has been an open problem for a long time. Here we study a class of Hubbard models on decorated lattices, which have a special property that the corresponding single-electron Schrödinger equation hasN _d-fold degenerate ground states. The degeneracyN _d is proportional to the total number of sites ||. We prove that the ground states of the models exhibit ferromagnetism when the electron filling factor is not more than and sufficiently close to=N _d/(2||), and paramagnetism when the filling factor is sufficiently small. An important feature of the present work is that it provides examples of three dimensional itinerant electron systems which are proved to exhibit ferromagnetism in a finite range of the electron filling factor.     

Ferromagnetism in doped excitonic insulators

The theory of doped excitonic insulators is reinvestigated in light of recent experiments on hexaborides. For the appropriate valley-degenerate X3,X'3 band structure, "intravalley" condensation is energetically favored. Ferromagnetism occurs upon doping due to the quenching of kinetic energy at the otherwise direct first-order excitonic insulator-metal transition. The phase diagram includes states of spatially inhomogeneous density and magnetization at low temperatures.     

Ferromagnetism in Cu-doped silicon carbide

Cu doped silicon carbide is shown to be ferromagnetic based on experiment results and first-principles calculations. The magnetization value of the Cu doped silicon carbide decreased as the Cu concentration increased. When the films were annealed at 800 °C, the ferromagnetic signal was increased. Reduction of the C vacancy concentration will introduce a large total moment in the system. Theoretically, compared with the case of one Cu atom replacing one Si atom, increasing the Cu doping, changing the Cu atom location or including carbon vacancies in the calculations for the system all make the ferromagnetic moment decrease. One Cu atom replacing one Si atom with the addition of one C vacancy makes the energy band gap of the system disappear. Our investigations suggest that the ferromagnetism arises from the hybridization between Cu 3d orbital and C 2p orbital. Ferromagnetic moment is influenced by a symmetry-lowering distortion of the surrounding lattice by the Cu dopant.     

Ferromagnetism in defective yttria-stabilized zirconia

Significant research attention has been devoted to identifying and synthesizing new magnetic materials via doping of non-magnetic materials. The material defects offer an approach to stabilize ferromagnetism in non-magnetic materials such as oxygen-deficient HfO₂ and oxygen-deficient ZrO₂. In this study, we demonstrated room-temperature ferromagnetism via nitrogen ion implantation on yttria-stabilized zirconia (YSZ) single crystals. The results of structural and chemical analyses indicate the formation of a distinct surface layer through the implantation of nitrogen ions and potential oxygen vacancies. The lattice constant in this surface layer increased by 0.6% compared to the bulk value. Nitrogen ions were observed in this region, and their concentration was estimated to be 2.32 atoms per unit cell. In contrast to the lack of magnetic hysteresis in a YSZ single crystal, ferromagnetic hysteresis was observed in the ion-implanted YSZ crystals, owing to defects—nitrogen ions and oxygen vacancies in the surface layer.     

Siberian Snake-Like Behavior for an Orbital Polarization of a Beam of Twisted (Vortex) Electrons

Physics of Particles and Nuclei Letters - The orbital polarization of twisted electrons carrying an intrinsic orbital angular momentum is not influenced by field perturbations in arbitrary magnetic...     

Ferromagnetism of Electron Gas

We here investigate the density and temperature dependence of polarization using the relativistic formalism for the electron–electron interaction within the Fermi liquid model. The variational method has been used: the free energy has been minimized with respect to the effective mass and the polarization parameter. Then we obtained the equation of state and magnetic susceptibility of the system. The exact results for polarization and magnetic susceptibility have been obtained at zero temperature. It has been shown that for a given temperature (density) there is a critical density (temperature) at which the ferromagnetic phase can appear in an electron gas. The results are in agreement with previous work. Our results show that at nonzero temperatures and in very low and very high densities the ferromagnetism phase cannot exist.     

Ferromagnetism of manganese compounds

It is shown on the basis of the notion of a strong electron-electron interaction in the unit cell that a ferromagnetic instability is possible in a system with hops between manganese cations and oxygen anions. The phase diagram for the existence of ferromagnetic ordering as a function of the degrees of underfilling n _p and n _t of the 2p ⁶ shell of oxygen and the 3t _g ⁶ shell of manganese, respectively, is constructed. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 254–259 (25 August 1997)     

Ferromagnetism of manganese compounds

The possibility of ferromagnetic instability in a system with hopping between manganese cations and oxygen anions has been investigated on the basis of the concept of strong electron-electron interaction in one unit cell. A phase diagram for ferromagnetic ordering as a function of the filling factors of the 2p ⁶-shell of oxygen (n _p ) and 3t ₆ ^g -shell of manganese (n _t ) has been constructed. Zh. éksp. Teor. Fiz. 113, 1101–1111 (March 1998)