Tm Metal Research Articles

Surface electronic structure of Tm(0001) and Yb(111).

Occupied d-like surface states were observed for the close-packed surfaces of Tm(0001) and Yb(111) metal films grown epitaxially on W(110) and Mo(110) substrates, respectively. In the case of Tm metal, the surface state exhibits almost no dispersion and is extended over the whole surface Brillouin zone, while in the case of Yb metal, it is restricted to a narrow region around the \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} point. The surface shifts of the 4f binding energies on these close-packed surfaces were determined to be 0.47\ifmmode\pm\else\textpm\fi{}0.05 eV for Tm(0001) and 0.45\ifmmode\pm\else\textpm\fi{}0.03 eV for Yb(111). Both values are substantially smaller than reported previously for polycrystalline surfaces of the two metals. State-of-the-art band-structure calculations, based on density-functional theory, predict a flat surface state slightly above the Fermi energy. There is no obvious explanation for this inconsistency at the present time.

Electronic relaxation observed in Mössbauer hyperfine spectra of Tm metal

Hyperfine seectra observed with the Mossbauer effect in Tm metal can be explained by an electronic relaxation mechanism. In contrast to an earlier analysis which assumed the fast relaxation limit, the present interpretation is based on a simpler picture and accounts for the spectra well throughout the entire temperature range from helium temperatures to room temperature.

Biosorption of cobalt with the AMT TM metal removing agent

The biosorption of cobalt from aqueous solutions was studied by using the novel metal removing agent (MRA) produced by Advanced Minerals Technologies. The parameters studied were the loading capacity of MRA as affected by the initial pH, cobalt concentration and the presence of certain cations and anions. The effect of temperature was also examined. With the particular batch of the MRA, it was found that the loading capacity for cobalt was about 35 mg/g. The cobalt uptake was a function of pH, and it was lower at lower pH values. Sorption kinetics showed that the sequestering of cobalt by this material was quite fast under ambient conditions. Desorption of cobalt from loaded MRA could be performed by dilute acids e.g. 0.1 N HCl in a very short period of time. The desorbed MRA could be recycled only after regeneration with alkali, for example, 0.5 N NaOH. A detailed mechanism of cobalt biosorption is also proposed.

The anomalies of optical properties of d- and f-transition metals during magnetic transformations

Abstract A review which covers the study of the optical response of 3d (Cr and its alloys) and 4f (Gd, Tb, Dy, Ho, Er, Tm) metals on magnetic “order-disorder” (FM-P, AFM-P) and “order-norder” (AFM-FM) phase transitions is presented. The influence of antiferromagnetic (AFM) transformations on optical properties of Cr and Cr-alloys with Mn, Fe, Co, Ru, Re is considered in detail. It is shown, that the process of formation of additional energy gaps in the AFM state is accompanied by a reduction of the number of electrons in the conduction bands. Estimates of “magnetic” gap magnitudes based on optical data are presented. The nature of band antiferromagnetism in Cr and its connection with the topology of Fermi surface is discussed. Peaks of resonance absorption in the near infrared region, observed in the optical conductivity spectra of some heavy rare earth metals are connected with quantum electron transitions between energy bands near the Fermi level split by s, d-f exchange interaction. The nature of the appearance of such peaks in AFM and FM states is analyzed taking into account specific features of the electronic structure and strong spin-orbital coupling in the rare earth metals.

Hyperfine interactions in amorphous Tm-Cu Alloys

Hyperfine interactions in sputtered amorphous TmxCu1−x, with x=0.70, 0.50, and 0.33, have been measured over a temperature range from 1.7 K to room temperature using the Mossbauer effect in169Tm. At low temperatures each spectrum shows a well resolved six-line hyperfine pattern indicative of magnetic order and a superimposed quadrupole doublet. The relative spectral weight of the magnetic component increases with increasing Tm concentration and decreases with increasing temperature. The magnetic component persists at unexpectedly high, temperatures with no decrease in overall splitting and no evidence of electronic relaxation. For all three concentrations, the magnetic splitting is the same as that of Tm metal at low temperatures, nearly the free-ion limit. The electric quadrupole shift of the magnetic component is the same for the three samples, but is significantly less than that of Tm metal (hexagonal) and much larger than that of crystalline TmCu (cubic). The non-magnetic doublets have quadrupole splittings that are very nearly the same for the three concentrations and show considerable asymmetry, a typical effect of electronic relaxation, which persists at temperatures above where the magnetic component disappears.

Experimental proof for coordination-dependent valence of Tm metal.

Photoemission measurements of Tm metal films (\ensuremath{\simeq} 1000 \AA{} thick) grown on a copper substrate at 13 K reveal a partial surface valence transition to the divalent $4{f}^{13}$ state. At room temperature, Tm films deposited on smooth substrates remain purely trivalent, whereas deposition on rough substrates yields small divalent components in the photoemission spectrum. This phenomenon is shown to occur for particularly low-coordinated atoms on rough surfaces, in quantitative agreement with thermochemical predictions.

A Mossbauer study of the cubic Laves phase intermetallic compound TmFe2

The results of a 169Tm and 57Fe Mossbauer study of the cubic Laves compound TmFe2 over the temperature range 1.3-550K are presented and discussed. The new results are used, in conjunction with existing NMR, Mossbauer and magnetic anisotropy data for TmFe2 and Tm metal, to deduce a value of P4f=536+or-14 MHz for the saturation value of the first excited state of the 169Tm nucleus. Estimates are also given for the exchange field mu BBex(T=0K)/kB=153+or-3K acting on the Tm3+ ion in TmFe2, the quadrupole moment of the I=3/2 state of the 169Tm nucleus, Q=-1.36+or-0.11 b, and the lattice contribution to the nuclear quadrupole interaction in Tm metal, Pc=-54.8+or-5 MHz (for Q=-1.20+or-0.07 b) and Pc=-61+or-8 MHz (for Q=-1.36+or-0.11 b). In addition, estimates are given for the various transferred and parent hyperfine fields in TmFe2.

Photoemission study of Tm metal

A photoemission investigation of Tm metal has been carried out using photon energies in the 100–200 eV range. Electron energy distribution curves and the photon absorption coefficient has been measured and the results are compared to earlier XPS and absorption measurements. No evidence of a valence change at the surface of Tm metal was found, a posibility proposed earlier.

X-ray absorption near edge structures of intermediate valence TmSe single crystals

L3 and L1 X-ray absorption spectra of single crystals of TmSe and Tm metal were measured at the synchrotron radiation facility PULS using the Frascati storage ring Adone. Valence fluctuations in TmSe appear from the analysis of the X-ray absorption near edge structures (XANES). The XANES of TmSe shows two well resolved 'giant resonances' at the L3 threshold due to 2p to 5, epsilon d* transitions localised on the Tm3+ and Tm2+ ions. The joint analysis of the L1 and L3 edges gives information on the symmetry of the conduction states near the Fermi level. The effects of the core-hole-induced relaxation on the measured intermediate valence are not important in Tm compounds. The values of the intermediate valence of Tm in TmSe can be extracted from XANES in contrast to what seems to be the case for Ce in intermediate valence Ce compounds.

Magnetic anisotropy in Gd-Tm alloys

The magnetization of single crystal binary Gd-Tm alloys were measured at 4.2 K in applied field up to 52 kOe along the three principal crystallographic directions. The magnetocrystalline anisotropy constants K02 and K04 were determined from the analysis of the hard magnetization curve on the basis of the molecular field theory. The values of K02 and K04 are negative and positive, respectively, in all concentration ranges, and both values increase quadratically with increasing Tm concentration in magnitude. From these results we estimated the value of the single ion anisotropy constant K02(R)SIA and anisotropic exchange interaction constant K02(R)AEI of the Tm metal. The values of K02(R)SIA and K02(R)AEI are −73 cm−1 and −60 cm−1, respectively. It may be assumed that the AEI contribution to K04 is approximately the same as K02.

Mössbauer study of 170Yb in some metals and metal-like compounds. Isomer shift measurements and intermediate valence states of ytterbium

We present here a Mössbauer effect study of the isomer shift and the magnetic behaviour of 170Yb in compounds with metallic character where the ytterbium valence state ranges from a practically divalent and diamagnetic state (Yb in Ag, Tm and Yb) to a trivalent magnetic state (Yb in Au). Intermediate valence states, all of them probably non-magnetic, have been observed in YbAl 2, TmAl 2, YbAl 3 and Al as well as in the borides YbB 4, YbB 12 and TmB 12. In Tm metal, in addition to the quadrupole interaction, a weak magnetic hyperfine interaction is visible on 170Yb below T N .

4f band energies in thulium

An apw calculation has been made giving the 4f band energies in h.c.p. Tm metal for four high symmetry values of k. Crystal field parameters are determined and compared with experimental results for dilute systems. It is then argued that this type of parametrication is inadequate for pure rare earth metals and should be replaced by a model in which the hybridization matrix elements between the 4f and conduction band are parameters.

Totalreflexion der rückstoßfreien 8,4 keV γ-Strahlung des Tm169

The total reflection of the recoilless 8.4 keVγ-radiation of Tm169 was observed at various glancing angles between 3 and 7 milliradians on surfaces of Tm metal and Tm2O3 produced by vacuum evaporation. The Mossbauer velocity spectra of the reflected intensity show a typical dispersion pattern due to interference between electronic and nuclear resonant scattering, which can be understood quantitatively, thus permitting the determination of the nuclear scattering amplitude. From this the total conversion coefficient of the 8.4 keV transition was derived to be α=220±50.

Analysis of the magnetic hyperfine structure observed using the Mössbauer effect in Tm metal

Complex Mössbauer-effect hyperfine spectra similar to those previously observed have been analyzed using a simple model based on the neutron diffraction solution of the magnetic structure. Previous difficulties in reconciling the observed spectra with this structure of Tm metal are resolved under the assumption of slightly incommensurate magnetic and crystal lattices.

Theory of Indirect Exchange Interactions in Rare-Earth Metals

Liu has recently considered the effect of nonzero atomic orbital angular momentum on the exchange interactions between a localized magnetic moment and conduction electrons. By expanding a part of the band wave functions in spherical harmonics, he found that the leading term gave rise to the familiar scalar product interaction between conduction electron spin and total atomic angular momentum J. In the present paper, we derive Liu's result by a simpler calculation, and obtain the first correction term in a similar expansion. Our main motivation in doing the latter is to investigate the validity of the common use of the leading term only, doubt being raised, a priori, by the fact that the Fermi wave vector times the radial extent of the $4f$ function is not \ensuremath{\ll}1. We then investigate, in second-order perturbation theory, the magnetic interaction between atoms $n$ and $m$. The leading term is, of course, an isotropic Heisenberg-type interaction $A_{\mathrm{nm}}^{}{}_{}{}^{(0)}{\mathbf{J}}_{n}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathbf{J}}_{m}$ corresponding to Liu's result. The first correction term gives rise to anisotropic interactions including pseudodipolar forces and an unconventional interaction which is quartic in the J's. An estimate for rare-earth metals, based on free conduction electrons and screened hydrogenic localized functions, suggests that the comparative importance of the correction term is very sensitive to the number of $4f$ electrons and also to the lattice structure. For Tb through Er, it appears that the leading term does dominate, the correction being roughly 10%; for Tm metal the correction term is \ensuremath{\sim}30%, whereas for a single pair of ${\mathrm{Tm}}^{3+}$ ions it is \ensuremath{\cong}80%. The leading term is also considered using the same type of one-electron functions. This gives roughly the right order of magnitude for the Curie temperature and the correct signs for first- and second-neighbor interactions; also the ratio of the latter interactions is in rough agreement with experiment.