Exchange interactions in rare-earth iron garnets

Exchange parameters previously reported for YbIG, ErIG and EuIG are compared. One of the three possible sets of parameters found for ErIG is shown to agree fairly well with the EuIG parameters and can also be fitted using an exchange potential. Tentative exchange potential parameters associated with the two types of superexchange pathways which couple the rare-earth ion to neighboring iron ions are obtained. A new method for calculating the YbIG exchange parameters is described and the parameters are compared with those reported previously.     

Magnetization measurements on some rare-earth iron garnets

The magnetic properties of Fe-based singlecrystal garnets have been studied. A magnetic field up to 55 kOe in the temperature range from 4.5 to 300 K has been used. The compensation temperature (T _comp) of the studied garnets has been determined. The compensation temperature increases with the increase of the rare-earth ions (Ho³⁺ or Gd³⁺) substituting Y³⁺ ions in thec sublattice of R₃Fe₅O₁₂. AboveT _comp, the magnetization was found to be linearly field dependent. The results are in good agreement with magnetization measurements performed on polycrystaline samples, and with calculations based on the crystal field parameters of the isostructural Holmium Gallium Garnet (HoGG).     

Electric field gradient in Cu2O from band structure calculations

We have performed self-consistent full potential LAPW calculations of Cu₂O. Since the new results agree well with a previous muffin-tin calculation, it can be concluded that non-muffin-tin effects are relatively small in Cu₂O. By using the present self-consistent charge density, we, obtain the electric field gradient (EFG) at the Cu site without further approximations. Our theory yields a value of −0.85 e/au³, in good agreement with experiment but in contrast to a previous cluster calculation in which a positive sign of the EFG was obtained. The origin of the EFG and the discrepancies between our band structure and the cluster calculation is analyzed.     

Heat capacity of rare-earth cuprates,orthovanadates, and aluminum garnets,gallium garnets,and iron garnets

Physics of the Solid State - The correlation between the heat capacities of rare-earth cuprates, orthovanadates, and garnets with ionic radius R 3+ has been analyzed. It has been shown that the...     

Aspherical 4f-shell effects in rare-earth metals: Electric field gradient at Dy probe nuclei

Systematic DPAC measurements of the electric field gradient at Dy in very low concentration in pure Pr, Nd, Gd, Tb, Dy, Ho and Er metals in the paramagnetic phase have shown for the first time the host associated aspherical 4f-shell effects. The results are compared with the presently available first-principles based calculations of the electric field gradient and crystalline electric field parameters of rare-earth ions in rare-earth metals and alloys. The observed 4f-spin relaxation time of Dy ion in rare-earth metals is of the order of 2 ps. This revised version was published online in August 2006 with corrections to the Cover Date.     

Interplay of iron and rare-earth magnetic order in rare-earth iron pnictide superconductors under magnetic field

The magnetic properties of iron pnictide superconductors with magnetic rare-earth ions under strong magnetic field are investigated based on the cluster self-consistent field method. Starting from an effective Heisenberg model, we present the evolution of magnetic structures on magnetic field in RFeAsO(R = Ce, Pr, Nd, Sm, Gd, and Tb) and RFe_2As_2(R =Eu) compounds. It is found that spin-flop transition occurs in both rare-earth and iron layers under magnetic field, in good agreement with the experimental results. The interplay between rare-earth and iron spins plays a key role in the magneticfield-driven magnetic phase transition, which suggests that the rare-earth layers can modulate the magnetic behaviors of iron layers. In addition, the factors that affect the critical magnetic field for spin-flop transition are also discussed.     

Dissolution forms of rare-earth gallium-aluminium garnets

Acta Physica Hungarica - Single crystal spheres of rare-earth gallium-aluminium garnet crystals (R3Al5?x Ga x O12, whereR=rare-earths and 0≤x≤5) have been dissolved in H3PO4 and...     

Electric field gradient studies in SnSe

The EFG in IV–VI compound semiconductor SnSe was studied using two hyperfine interaction techniques, namely, TDPAC and Mössbauer spectroscopy. The EFG in this material increases sharply up to 300 K and thereafter at higher temperatures it gets saturated. However, the conductivity increases steadily at all the temperatures. The conductivity curve has two slopes. The first portion is due to the population of shallow Cd acceptor levels. Thus, in SnSe also the variation of the EFG with temperature is complex, as in other medium-gap semiconductors.

     

Electric field gradient effects in raman spectroscopy

Raman spectra of materials subject to strong electric field gradients, such as those present near a metal surface, can show significantly altered selection rules. We describe a new mechanism by which the field gradients can produce Raman-like lines. We develop a theoretical model for this "gradient-field Raman" effect, discuss selection rules, and compare to other mechanisms that produce Raman-like lines in the presence of strong field gradients. The mechanism can explain the origin and intensity of some Raman modes observed in SERS and through a near-field optical microscope (NSOM-Raman).     

Electric field gradient in dilute vanadium alloys

The electric field gradient (EFG) and the asymmetry parameter due to transition-metal impurities Ti, Cr, Fe, Nb, Ta and W in a host metal V, have been calculated. The size effect contribution to EFG is estimated using the continuum theory of elasticity, and the valence-effect contribution is evaluated using the dielectric screening theory. It is found that the asymmetry parameter is zero in alloys with bcc structure and the valence-effect contribution dominates the size-effect contribution, which are novel features.     

Electric field gradient in transitional dilute alloys

The electric field gradient (EFG) and the asymmetry parameter (η) due to transition metal impurities in the host metals Al, Cu and V are investigated. The valence EFG is formulated using dielectric screening theory in conjunction with pseudopotential theory. The size EFG is evaluated in the elastic continuum limit for a screened point charge model of the host metal. The detailed calculations are carried out forAl (Sc, Fe, Cr),Cu (Ni, Pd, Pt) andV (Ti, Cr, Fe, Nb, Ta, W) alloys.     

Magnetooptics of magnetic-dipole transitions in the rare-earth paramagnetic garnets

The Faraday effect (FE) of the rare-earth (RE) paramagnetic garnet crystals associated with magnetic-dipole (MD) transitions has been investigated theoretically over a wide temperature range 80 to 300 K. Over this temperature range, the ??gyromagnetic?? Verdet V _gm ^(m) of the Eu₃Ga₅O₁₂ (EuGG) is not a linear function of the magnetic susceptibility ?? measured along the [111] axis. We find that the nontrivial character of the temperature dependence of the MD Verdet constant V _gm ^(m) is associated with the presence of a contribution to the Faraday rotation of the Van Vleck ??mixing?? by an external magnetic field of the Eu³⁺ electronic states. The optical absorption and magnetic circular dichroism (MCD) of Eu³⁺ ion in EuGG at 85 K for the MD transition ⁷ F ₀ ?? ⁵ D ₁ were measured along the [111] axis. We show that the appearance of the MCD feature observed for the absorption line near 526.6 nm for the ⁷ F ₀ ?? ⁵ D ₁ MD absorption band may be well-explained by the contribution of Van Vleck ??mixing?? between the Stark singlet states from the ⁷ F ₀ and ⁷ F ₁ multiplet manifolds mixed by the external magnetic field H.     

Problems with the F-tensor in electric field gradient calculations

A rigorous derivation of the F-tensor coefficient F_ij-relating the strain to the electric field gradient (EFG) — is given for polyvalent FCC and BCC hosts. It is shown that Faulkner’s results are valid only for a monovalent FCC host. Results for F_ij are also obtained when the inter-ionic potential is screened Coulomb type. Comparing these with those in the literature, errors are pointed out and problems are discussed.     

Electric field gradient in pure hexagonal transition metals

Using a general calculation of the nuclear quadrupole interaction in non-cubic metals which was presented in a previous paper, this article gives an interpretation of experimental data dealing with signs and temperature dependence of the electric field gradient in 3d(Sc, Ti), 4d(Y, Zr, Tc, Ru) and 5d (Hf, Re, Os) transition hexagonal close-packed metals.     

Electric field gradient in transition metal — scandium

Electric field gradient inhcp transition metal scandium has been calculated as the sum of contributions from lattice ions and conduction electrons. For the lattice contributionq _latt, a point-charge model has been assumed. The contribution from conduction electronsq _el, on the other hand, has been evaluated by carrying out an energy-band calculation using non-local transition-metal model potential. The results obtained are:q _el=−106.11×10¹³ esu/cm³ andq _latt=122.17×10¹³ esu/cm³. The net field gradient (q _el+q _latt) of 16.06×10¹³ esu/cm³ agrees quite well with the experimental result, |q _expt|=13×10¹³ esu/cm³. Directions of further improvement in the theory are discussed.     

Electric field gradient in transition metal: Scandium

Corrections to results of electric field gradient (EFG) already published [Pramana — J. Phys.41, 443 (1993)] are reported. The corrected net EFG is:q=−8.01×10¹³ esu/cm³ against the published valueq=16.06×10¹³ esu/cm³. The present result agrees reasonably well with the experimental result, |q _expt|=13×10¹³ esu/cm³. Recently, a computational error is detected, which modifies the results of EFG, we have already published [1]. The error was committed mainly in the part that evaluated thep-p contribution [1] to EFG by the conduction electrons. The corrected results are summarized in table 1 which must replace the table 1 of the published work [1]. In addition, the lattice parameters as well as the temperature were also misquoted in the previous work [1]. The right parameters are:a=6.25311 au andc=9.96509 au. The temperature at which EFG’s are calculated is 293 K instead of 11 K as reported before [1]. The discussions and conclusions made in the published work [1] remain almost unchanged except that they now refer to the corrected numbers. Although the corrected net EFG suffers a sign reversal from the one already published [1], the agreement with experiment is still considered reasonably good because the sign of experimental EFG is not determined. The computational error however does not affect the introduction and theory section of the published work [1].