First-principles investigation of the electronic structure and magnetism of Heusler alloys CoMnSb and Co2MnSb

The spin-polarized electronic band structures, density of states (DOS), and magnetic properties of Co-Mn-based Heusler alloys CoMnSb and Co₂MnSb have been studied by first-principles method. The calculations were performed by using the full-potential linearized augmented plane wave (FP-LAPW) within the spin-polarized density functional theory and generalized gradient approximation (GGA). Calculated electronic band structures and the density of states are discussed in terms of the contribution of Co 3d⁷4s², Mn 3d⁵4s², and Sb 5s²5p³ partial density of states and the spin magnetic moments were also calculated. The results reveal that both CoMnSb and Co₂MnSb have stable ferromagnetic ground state. They are ideal half-metallic (HM) ferromagnet at their equilibrium lattice constants. The calculated total spin magnetic moments are 3μ_B for CoMnSb and 6μ_B for Co₂MnSb per unit cell, which agree with the Slater-Pauling rule quite well.     

169Tm Mössbaüer spectroscopy and crystal field calculations in TmNi3 and TmCo3 intermetallics

The values of the magnetic moments and the electric field gradient in TmNi₃ and TmCo₃ are obtained from ¹⁶⁹Tm Mössbauer spectroscopy. These values are compared to those from crystal field model based on point charge calculations for these intermetallics.     

Heavy-ion excitation of 3− states in deformed nuclei

Previously measured data for 70.4 MeV ¹²C excitation of 3^? states in ^{148, 150}Nd are reanalyzed using a third-order rotational-vibrational model. Calculations using 3^? quadrupole moments which are expected if they are K = 0 states are in reasonable agreement with the magnitude of the large-angle data, but the quality of the fit in the Coulomb-nuclear interference region is only fair. It is found that the matrix element 〈2⁺∥M(E3)∥3^?〉 plays an important role in the calculations making the “measurement” of the 3^? quadrupole moments very difficult, if not impossible.     

Magnetic moments of high-spin states above the rotational band of 168Hf and 172Hf

The transient magnetic field IMPAC technique was used to measure the magnetic moments of high-spin states above the rotational band of ¹⁶⁸Hf and ¹⁷²Hf, populated in the reactions ^{156, 160}Gd(¹⁶O, 4n). The average g-factors of these prerotational feeding states were deduced to be 0.07 ± 0.04 and 0.14 ± 0.04 for ¹⁶⁸Hf and ¹⁷²Hf, respectively. These results are in agreement with a reduction of the collective g-factors due to a neutron phase transition.     

Hyperfine structure and nuclear moments of99Ru and101Ru

The atomic-beam magnetic-resonance method in combination with the triple resonance technique has been used to determine the nuclear magnetic dipole moments of⁹⁹Ru and¹⁰¹Ru. The moments are deduced fromrf transition measurements in the⁵F₅ and⁵F₄ states at magnetic fields between 770 and 2400 Oe. In order to reduce the part of the uncertainty of the moments which arises from the uncertainty of the hyperfine structure constants more precise values of the constants than those available up to now were determined from low field measurements. After making corrections for hyperfine and Zeeman interactions with neighbouring atomic states we obtain the following values for the magnetic dipole moments:μ ₉₉=?0.6381 (51)μ _N andμ ₁₀₁=?0.7152 (60)μ _N (uncorrected for diamagnetic shielding). The results of the present work combined with the results of an earlier hyperfine structure investigation in the⁵F multiplet are analysed with respect to the effective-operator formalism. From this analysis we obtain the following values for the electric quadrupole moments:Q ₉₉=0.076 (7) b andQ ₁₀₁=0.44 (4) b (uncorrected for Sternheimer shielding or antishielding).     

Beta-NMR/ON on-line at the NICOLE facility, ISOLDE –recent magnetic moment studies near double magic 68Ni

The technique of β-NMR/ON and its use for measurement of nuclear magnetic moments is briefly reviewed. Recent magnetic moment measurements are reported on ⁶⁷Ni and ⁶⁷Cu. The relevance of magnetic moments of single-particle (hole) states for study of effects of configuration mixing and mesonic exchange currents is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Theoretical study of the transition probabilities among the three lowest electronic states of the SeS molecule

Spin-perturbed CI wavefunctions are reported for the X ³Σ^? electronic states of the SeS molecule. The Breit-Pauli approach is employed using the one- and two-electron spin-orbit operator as the perturbing hamiltonian and a zeroeth-order basis of CI eigenfunctions generated by the standard multireference single- and double-excitation (MRD-CI) formalism. Transition moments are reported between each of the above states for electric and magnetic dipole and electric quadrupole radiative processes, and these results are compared with recent experimental high resolution data obtained by Fink, Kruse, Ramsay and Wang. Generally good agreement is found between computed and observed ratios of such quantities, but the absolute values of the computed transition moments are uniformly found to be only somewhat less than half as large as the corresponding observed results. A simple formula is presented which relates the magnetic moments of the b ¹Σ⁺-X ³Σ1? transitions to twice the square root of the ratio of two observable energy differences and this result promises to be useful in future experimental studies attempting to estimate line strengths for this type of band system. On this basis arguments are also presented supporting the view that the computed absolute intensities may be more accurate than would appear from the original experimental assessment of the SeS spectroscopic data.     

Effects of electron correlation and spin-orbit coupling on the electronic and magnetic properties of TbCu3Mn4O12

Electronic and magnetic properties of the three magnetic-sublattice double perovskite TbCu₃Mn₄O₁₂ (TCMO) are investigated by performing first-principles density-functional theory calculations. Our electronic structure calculations show that TCMO is half-metallic and its half-metallicity can only be correctly described when the electron correlation on Tb³⁺ 4f⁸ electrons are considered. The energies of different magnetic configurations among the three magnetic sublattices are also calculated, revealing that the magnetic configuration with Mn and Cu spins in the antiparallel arrangement and with the Tb magnetic moments ferromagnetically/antiferromagnetically (FM/AFM) coupled to Cu/Mn spins (that is Tb^↓Cu₃^↓Mn₄^↑O₁₂) is the lowest energetic magnetic state, which is consistent with recent experimental results. The magnetic anisotropy is further calculated for the [1 1 1], [1 1 0], and [0 0 1] spin quantization directions. It is found that the [1 1 1]-direction is more stable than the [1 1 0]- and [0 0 1]-directions by 123 and 135 meV per formula unit, respectively, indicating a significant magnetic anisotropy. Our detailed projected partial density of states analysis finally shows that Cu and Mn are antiferromagnetically coupled by superexchange interaction and Tb is expected to interact FM with A-site Cu and AFM with B-site Mn sublattices by way of 4f-2p-3d.     

Magnetic moments of 127gTe and 129gTe

Anisotropies of several γ-rays in the decay of ^127gTe and ^129gTe implanted in iron, have been observed in nuclear orientation experiments. The magnetic moments of both ground states were derived: μ($\text{3}\text{2}$⁺) = 0.66 ± 0.05 n.m. for ^127gTe and μ($\text{3}\text{2}$⁺) = 0.66 ± 0.05 n.m. for ^129gTe. These results, compared to predictions from pairing-plus-quadrupole theory, suggest a pure single-quasiparticle character for these states.     

Negative-parity states of75As and the interacting boson-fermion model

The result of an IBFM multilevel calculation with the 2p_3/2, 1f_5/2 and 2p_1/2 single particle orbits is reported for the negative parity states of the odd mass nucleus⁷⁵As. Comparisons are made with experimental data for energy spectra, transition probabilities, mixing ratios, electric quadrupole and magnetic dipole moments. Also, an IBM-1 calculation is presented for the low-lying states in the even-even⁷⁴Ge core nucleus.     

Influence of magnetic ordering on electronic structure of Tb<Superscript>3+</Superscript> ion in TbFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> crystal

Optical absorption spectra of trigonal crystal TbFe₃(BO₃)₄ have been studied in the region of ⁷F₆ → ⁵D₄ transition in Tb³⁺ ion depending on temperature (2–220 K) and on magnetic field (0–60 kOe). Splitting of the Tb³⁺ excited states, both under the influence of the external magnetic field and effective exchange field of the Fe-sublattice, have been determined. Landé factors of the excited states have been found. Stepwise splitting of one of the absorption lines has been discovered in the region of the Fe-sublattice magnetic ordering temperature. This is shown to be due to the abrupt change of equilibrium geometry of the local Tb³⁺ ion environment only in the excited state of the Tb³⁺ ion. In general, the magnetic ordering is accompanied by temperature variations of the Tb³⁺ local environment in the excited states. The crystal field splitting components have been identified. In particular, it has been shown that the ground state (in D ₃ symmetry approximation) consists of two close singlet states of A ₁ and A ₂ type, which are split and magnetized by effective exchange field of the Fe-sublattice. Orientations of magnetic moments of the excited electronic states relative to that of the ground state have been experimentally determined in the magnetically ordered state of the crystal. A pronounced shift of one of absorption lines has been observed in the vicinity of the TbFe₃(BO₃)₄ structural phase transition. The temperature interval of coexistence of the phases is about 3 K.     

TmTO3 (T = Al, Fe, CrandV). A 169Tm Mössbauer study of magnetic and crystal field properties

¹⁶⁹Tm Mössbauer measurements are reported for the distorted perovskite compounds TmAlO₃, TmFeO₃, TmCrO₃ and TmVO₃ and have been analyzed to provide information concerning the crystal field and magnetic properties of the Tm³⁺ ion. Tm³⁺ has no magnetic moment in TmAlO₃ and low temperature saturated moments of 0.09, 0.8 and 2.1μ_B in TmFeO₃, TmCrO₃ and TmVO₃, respectively. In TmFeO₃ and TmCrO₃ the magnitudes and directions of the Tm³⁺ moments are examined in terms of previously proposed magnetic structural models. In TmVO₃, the crystal field properties are very different to those in the ferrite and chromite and a reorientation of the Tm³⁺ magnetic moments, accompanied by a sharp increase in their size, is observed near 10 to 15 K.     

Magnetic ground state and the spin-state transitions in YBaCo<Subscript>2</Subscript>O<Subscript>5.5</Subscript>

The crystal and magnetic structure of the perovskite-like, oxygen deficient cobalt oxide YBaCo₂O_5.5 has been studied by means of neutron and X-ray diffraction in the 10–300 K temperature range. The magnetic ground state is characterized by a coexistence of two distinct antiferromagnetic phases. In the first one, the ionic moments of high-spin Co³⁺ ions in the pyramidal sites are ordered in a spiral arrangement, while octahedral sites are non-magnetic due to presence of low-spin Co³⁺ ions. The arrangement in the second phase is collinear of the G-type, with non-zero moments both in pyramidal (high-spin Co³⁺ ions) and octahedral sites (presumably a mixture of the low- and high-spin states). With increasing temperature, at 260–300 K, the system develops a gradual structural transformation, which is associated with appearance of spontaneous magnetic moment. This process is related to a thermally induced reversion of low- and high-spin states at the octahedral sites to the intermediate-spin Co³⁺ states, resulting in an insulator-metal transition at T_C ≈ T_IM ≈ 295 K.     

The effect of particle-vibration coupling due to the collective 2+ state on the magnetic moments of Tl-isotopes

The mass number dependence of magnetic moments of Tl-isotopes is studied by taking into account the effect of the first 2⁺ states of Pb-isotopes in the framework of the particle-vibration coupling model. It is shown that a significant difference of magnetic moments of ²⁰⁷Tl to ^203,205Tl can be understood by the difference in the excitation energies of the collective 2₁⁺ states between ²⁰⁸Pb and ^204,206Pb.     

Spin and orbital moments in Upt3

The local spin-density functional approximation is used to calculate the electronic structure of UPt₃ in assumed non-magnetic, ferromagnetic and antiferromagnetic ground states. When spin-orbit coupling is included it is found to induce orbital moments which to a large extend compensate the spin moments of the initially magnetic ground states.     

Neutron-proton differences in the excitation of 104Ru from high-resolution polarized deuteron scattering

The low-excitation spectrum of ¹⁰⁴Ru, which provides strong evidence for a triaxial shape of the nucleus, has been investigated by high-resolution inelastic scattering of 23 MeV polarized deuterons. The 2⁺₂−4⁺₁ doublet with an energy separation of only 4.6 keV has been resolved using the Q3D magnetic spectrograph. From the coupled-channel analysis of the data, isoscalar transition moments are obtained which yield by comparison with the electromagnetic properties the neutron moments of the transitions. For the excitation of the 2⁺₁ and 2⁺₂ states we find substantial differences between corresponding proton and neutron moments.     

Orbital-decomposed electronic and magnetic properties of the double perovskite Sr2FeReO6

The detailed orbital-decomposed electronic structures and magnetic properties of the double perovskite Sr₂FeReO₆ have been studied using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA). Both occupied and unoccupied s and three p states of Fe³⁺ ion are located far away from the Fermi level, while all up-spin states and most down-spin states are completely filled for the s and three p states of Re⁵⁺ ion. The octahedral crystal field of the oxygen atoms around transition-metal (TM) sites splits the five-fold degenerate d states of the free TM atoms into triply degenerate t_2g states with smaller bonding-antibonding splitting and doubly degenerate e_g states with larger bonding-antibonding splitting. The Fe³⁺ and Re⁵⁺ ions are in the states (3d⁵, S=5/2) and (5d², S=1) with magnetic moments 3.70 and −0.86μ_B, respectively and thus antiferromagnetic coupling via oxygen between them. There are no direct interactions between two nearest Fe-Fe or Re-Re pairs, whereas along each Fe-O-Re-O-Fe or Re-O-Fe-O-Re chains, the hybridizations between Fe 3d and 4s, O 2s and 2p, as well as Re 5p, 5d and 6s orbitals are fairly significant.