First-principles study on the magnetism in ZnS-based diluted magnetic semiconductors

The electronic and magnetic properties of wurtzite ZnS semiconductor doped with transition metal (Cr, Mn, Fe, Co, and Ni) atoms are studied by using the first-principle’s method in this paper. The ZnS bulk materials doped with Cr, Fe, and Ni are determined to be half-metallic, while those doped with Mn and Co impurities are found to be semiconducting. These doped transition metal ions have long range interactions mediated through the induced magnetic moments in anions and cations of host semiconductors. These doped ZnS-based diluted magnetic semiconductors seem to be good candidates for the future spintronic applications.     

Effects of the 3d transition metal doping on the structural,electronic, and magnetic properties of BeO nanotubes

First-principles calculations have been performed on the structural, electronic, and magnetic properties of seven 3d transition-metal(TM) impurities(V, Cr, Mn, Fe, Co, Ni, and Cu) doped armchair(5,5) and zigzag(8,0) beryllium oxide nanotubes(BeONTs). The results show that there exists a structural distortion around the 3d TM impurities with respect to the pristine BeONTs. The magnetic moment increases for V- and Cr-doped BeONTs and reaches a maximum for Mn-doped BeONT, and then decreases for Fe-, Co-, Ni-, and Cu-doped BeONTs successively, consistent with the predicted trend of Hund’s rule to maximize the magnetic moments of the doped TM ions. However, the values of the magnetic moments are smaller than the predicted values of Hund’s rule due to the strong hybridization between the 2p orbitals of the near O and Be ions of BeONTs and the 3d orbitals of the TM ions. Furthermore, the V-, Co-, and Ni-doped(5,5) and(8,0) BeONTs with half-metal ferromagnetism and thus 100% spin polarization character are good candidates for spintronic applications.     

Impurity atoms in small metallic particles

The effect of self-purification has been discovered in small metallic particles containing impurity atoms. Due to small dimension of the particles impurities were shown to get out of the particles and to reach its surface in relatively short times. The phenomenon has been studied for small particles of Li containing Na atoms as impurities and for NiCu alloy particles. The distribution of atoms in lithium particles was studied by the ESR method and the information about the distribution of Ni atoms within CuNi alloy particles was obtained by comparing the structure date with magnetic properties.     

Synergetic effects of impurities and alloying element Cr on oxidation and dissolution corrosion of Ni (111) surfaces: A DFT study

Using density-functional calculations, we studied the interactions between interstitial impurities (H, O, N, S, and P) and Ni (111) surfaces doped, or not, with Cr, and studied the effect of Cr doping on the dissolution corrosion resistance of Ni(111) surfaces. The aim of this work was to study, at the atomic scale, the effects of Cr on the segregation behaviors of impurities and the synergetic effects between co-doped atoms on the resistance to dissolution corrosion of Ni (111) surfaces. The results indicate that impurities S, P, O, and H prefer to be trapped at near-surface sites, that Cr was uniformly distributed in the Ni crystal and can affect the segregation behavior of impurities S and P to move toward the surface, and it affects impurities N and O such that they shift from the surface to the subsurface. The formation of near-surface Cr nitrides (speculated to be Cr₂N based on the results obtained for particular co-doped surfaces) was also noted. Introducing Cr enhances the structural stability of the Ni (111) surface and protects it from being corroded when impurities are present. The elementary processes studied afforded microscopic insights into the formation of a Cr-depleted zone, a phenomenon that leads to local corrosion of the Ni alloy surface. The results of our theoretical calculations explain some of the experimental results previously observed at the atomic scale.     

Magnetic susceptibility of CdSb doped with Mn,Fe, Ni and La

This paper is devoted to the study of the temperature dependence of the magnetic susceptibility of CdSb doped with Mn, Fe, Ni and La. Analyzing the measured curves on the assumption that the impurities are substitutional and using the Hall constant measurements, we were able to determine the magnetic moments of Fe and Ni impurities and to obtain some information concerning the bond of these atoms with their nearest neighbours. The impurities Mn and La are dissolved in CdSb only partly as substitutional impurities, the major part most probably forming with antimony a new phase which is strongly paramagnetic and fully overgrows the diamagnetism of the parent semiconductor compound.     

Magnetic behaviour of isolated Fe and Ni ions measured directly after implantation into II-VI-semiconductors

Abstract

The local magnetic behaviours of isolated Fe and Ni impurities in the II-VI semiconductors ZnS and ZnTe have been studied directly after recoil implantation. From the measured magnetic properties, which are detected by the observation of the perturbed angular distribution, orbital contributions to the hyperfine field as well as contributions from spin magnetism are found to be present at both impurities. The interpretations on the basis of the intermediate ligand field model suggest that Fe and Ni ions are found to exist in 2+ and in 1+ states and that electronic excitations may play a significant role even microseconds after the implantation.     

Tracer impurity diffusion in single-crystal rutile (TiO2−x)

By means of the radioactive-tracer sectioning technique, the tracer diffusion of the impurity ions, ⁴⁶Sc, ⁵¹Cr, ⁵⁴Mn, ⁵⁹Fe, ⁶⁰Co, ⁶³Ni and ⁹⁵Zr, in rutile single crystals was measured as functions of crystal orientation, temperature, oxygen partial pressure and Al impurity content. The diffusion coefficients are very sensitive to the electric charge of the impurity ions. Divalent impurities (e.g., Co and Ni) diffuse extremely rapidly in TiO₂, compared to cation self-diffusion, and exhibit an extreme anisotropy in diffusion behavior, divalent-impurity diffusion parallel to the c-axis is much larger than it is perpendicular to the c-axis. Trivalent impurity ions (Sc and Cr) and tetravalent impurity ions (Zr) diffuse similar to cation self-diffusion, both as functions of temperature and oxygen partial pressure. The divalent impurity ions Co and Ni apparently diffuse as interstitial ions along open channels parallel to the c-axis. The results suggest that Sc, Cr and Zr ions diffuse by an interstitialcy mechanism involving the simultaneous and cooperative migration of tetravalent interstitial titanium ions and the tracer-impurity ions. Iron ions diffuse both as divalent and as trivalent ions. The impurity diffusion as functions of oxygen partial pressure and Al-impurity content are consistent with calculations of point-defect concentrations in rutile.     

Magnetic dipole transitions in highly ionized titanium,chromium, iron and nickel

Wavelengths of magnetic dipole transitions in the ground configurations of Ti, Cr, Fe and Ni ions in fluorine through beryllium isoelectronic sequences have been measured in tokamak plasmas.     

Ground state valency and spin configuration of the Ni ions in nickelates

The ab initio self-interaction-corrected local-spin-density approximation is used to study the electronic structure of both stoichiometric and nonstoichiometric nickelates. From total energy considerations it emerges that, in their ground state, both LiNiO2 and NaNiO2 are insulators, with the Ni ion in the Ni3+ low-spin state (t(2g)(6)e(g)(1)) configuration. It is established that a substitution of a number of Li/Na atoms by divalent impurities drives an equivalent number of Ni ions in the NiO2 layers from the Jahn-Teller (JT)-active trivalent low-spin state to the JT-inactive divalent state. We describe how the observed considerable differences between LiNiO2 and NaNiO2 can be explained through the creation of Ni2+ impurities in LiNiO2. The indications are that the random distribution of the Ni2+ impurities might be responsible for the destruction of the long-range orbital ordering in LiNiO2.     

Hyperfine Fields of Light Interstitial Impurities in Ni

The magnetic hyperfine interaction of light interstitial impurities in Ni have been studied by means of the Korringa–Kohn–Rostoker (KKR) band structure method. This method allows to deal with the impurity problem by solving the corresponding Dyson equation for the Green’s function. It also allows to account for lattice relaxations. For this purpose a new technique was developed that allows to handle in principle arbitrary lattice distortions. Corresponding calculations have been performed for the magnetic hyperfine fields of the light interstitial impurities H to Ne in Ni. By minimising the force on the nearest neighbour host atoms their equilibrium position was determined. The resulting hyperfine fields for the equilibrium configuration are found to be in rather good agreement with available experimental data.     

Radiative color centers in doped sapphire crystals

Experimental and theoretical results of investigation of the spectral properties of sapphire (α-Al₂O₃) single crystals are analyzed. Crystals grown under different conditions, both nonactivated and activated with impurity ions of the iron group (Cr, V, Mn, Fe, Co, Ni), primarily with chromium ions, were investigated before and after irradiation with photons and high-energy electrons. It is shown that the impurity composition of crystals significantly affects the radiative and optical properties and the character of changes in the electronic state of impurities.     

Nickel impurity-induced enhancement of the pseudogap of cuprate high-T(c) superconductors

The influence of magnetic Ni and nonmagnetic Zn impurities on the normal-state pseudogap (PG) in the c-axis optical conductivity of (Sm,Nd)Ba(2){Cu(1-y)(Ni,Zn)(y)}(3)O(7-delta) crystals was studied by spectral ellipsometry. We find that these impurities, which strongly suppress superconductivity, have a profoundly different impact on the PG. Zn gives rise to a gradual and inhomogeneous PG suppression while Ni strongly enhances the PG. Our results challenge theories that relate the PG either to precursor superconductivity or to other phases with exotic order parameters, such as flux phase or d-density wave states, that should be suppressed by potential scattering. The apparent difference between magnetic and nonmagnetic impurities instead points towards an important role of magnetic correlations in the PG state.     

Atomic displacements in dilute alloys of Cr, Nb and Mo

Kanzaki lattice static method is used to calculate the atomic displacements due to substitutional impurities in 3d (Cr) and 4d (Nb, Mo) metals. Wills and Harrison interatomic potential is used to calculate dynamical matrix and the impurity-induced forces up to second nearest neighbors. The calculated atomic displacements for 3d, 4d and 5d impurities in Cr (V, Mn, Fe, Ni, Nb, Mo, Ta and W), Nb (V, Cr, Mn, Fe, Zr, Mo, Ta and W) and Mo (V, Cr, Mn, Fe, Zr, Nb, Ta and W) are tabulated up to 10 NN’s. The strain field due to 3d impurities is least in Cr metal while it is larger in Nb and Mo metals. For 4d and 5d impurities the strain is larger in Cr metal than in Nb and Mo hosts. Similar trend is found for relaxation energies also.     

Faraday effect and aggregation of paramagnetic ions in borate glasses

The magneto-optical Faraday effect and electron spin resonance (ESR) in a potassium-aluminum borate glass containing small amounts of impurities of Fe and Mn oxides have been investigated. The Faraday effect measurements and ESR data made it possible to reveal the formation of clusters of paramagnetic ions interacting via oxygen even in the stage of glass synthesis. Heat treatment leads to cluster coarsening and formation of nanoparticles.     

天然方解石的定代和顺磁共振研究

用ESR分析了天然方解石(CaCO₃)中的杂质Mn²⁺离子和天然顺磁缺陷的性质。有关谱的理论计算基本和实验结果一致.解释了热处理和辐照样品出现的一些实验现象,最后提出了如何克服干扰解决含有一些杂质Mn²⁺离子样品的定代问题。     

Local spin density in the Cr(7)Ni antiferromagnetic molecular ring and (53)Cr-NMR

We present (53)Cr-NMR spectra collected at low temperature in a single crystal of the heterometallic antiferromagnetic (AF) ring Cr(7)Ni in the S?=?1/2 ground state with the aim of establishing the distribution of the local electronic moment in the ring. Due to the poor S/N we observed only one signal which is ascribed to three almost equivalent (53)Cr nuclei in the ring. The calculated spin density in Cr(7)Ni in the ground state, with the applied magnetic field both parallel and perpendicular to the plane of the ring, turns out to be AF staggered with the greatest component of the local spin ?s? for the Cr(3+) ions next to the Ni(2+) ion. The (53)Cr-NMR frequency was found to be in good agreement with the local spin density calculated theoretically by assuming a core polarization field of H(cp)?=-?11?T/μ(B) for both orientations, close to the value found previously in Cr(7)Cd. The observed orientation dependence of the local spin moments is well reproduced by the theoretical calculation and evidences the importance of single-ion and dipolar anisotropies.     

On the theory of impurities in a lattice of magnetic ions: Crystalline field effects

We present a formalism for treating the problem of impurities in a lattice of magnetic rare earth ions. Latter are subject to a crystalline field and special attention is paid to non-Kramers ions in a singlet ground state. Our calculations are restricted to the paramagnetic regime. We derive the conditions for magnetic localized modes to occur and discuss the appearance of local magnetic instabilities. It is shown that the impurity effects are especially large if the system is close to a magnetic phase transition. Furthermore we compute the influence of impurities on the magnetic transition temperature. For the case of vacancies or nonmagnetic impurities the dependence of the Curie temperature on impurity concentration is derived. It is demonstrated that small amounts of impurities can often completely suppress magnetic ordering.     

Effect of structural distortions on the magnetism of doped spin-Peierls CuGeO3

The chemical selectivity and great sensitivity of the Extended X-ray Absorption Spectroscopy technique allowed the determination, in the paramagnetic phase, of the structural distortions induced by doping in the spin-Peierls CuGeO₃ compound. The distorted environments were analyzed as a function of concentration, magnetic nature of impurity and the substitution site (Ni, Mn and Zn impurities on the Cu site, Si impurity on the Ge site). This has led to estimate the variation of the angles and pair distances, and hence to evaluate the magnetic coupling along the Cu chains in the vicinity of the impurities. The antiferromagnetic interaction between Cu first neighbors in the pure sample is found to be weakened around Ni, almost cancelled in the case of Mn doping, and even to change sign, producing a ferromagnetic coupling for Si doping. More generally, the structural distortions on a local scale are shown to be key parameters for the understanding of the magnetic properties of doped spin-Peierls compounds.     

Magnetic behavior of na films with Fe, Co, and Ni impurities

Thin films of Na with Fe, Co, and Ni impurities are investigated. The magnetization of the impurities is measured by means of the anomalous Hall resistance. Fe and Co show a moment of about 6mu(B), while for Ni no moment is detected. Furthermore, the magnetic dephasing of the conduction electrons is measured by means of weak localization. The dephasing rate 1/tau(phi) of the 3d impurities differ qualitatively. For Fe impurities, 1/tau(phi) is so large that it cannot be measured. For Co, 1/tau(phi) has a moderate value while Ni shows hardly a dephasing effect at all.     

Electron Spin Resonance Measurements of a Demagnetizing Field on the Surface of Metal Samples

By comparing the signals of electron spin resonance (ESR) from two crystals of a diamond (spin–labels) the demagnetizing field of the Co, Fe, and Ni samples in the shape of strongly elongated ellipsoids of revolution (disks) has been measured. The magnetic permeabilities of the metals in the external magnetic field corresponding to the ESR of the broken chemical bonds in a natural diamond irradiated with fast reactor neutrons have been determined.