Structure Of Rare Earth Metals Research Articles

Magnetic and Structural Phase Transitions in Thulium under High Pressures and Low Temperatures

The nature of 4f electrons in many rare earth metals and compounds may be broadly characterized as being either “localized” or “itinerant”, and is held responsible for a wide range of physical and chemical properties. The pressure variable has a very dramatic effect on the electronic structure of rare earth metals which in turn drives a sequence of structural and magnetic transitions. We have carried out four-probe electrical resistance measurements on rare earth metal Thulium (Tm) under high pressures to 33 GPa and low temperatures to 10 K to monitor the magnetic ordering transition. These studies are complemented by angle dispersive x-ray diffraction studies to monitor crystallographic phase transitions at high pressures and low temperatures. We observe an abrupt increase in magnetic ordering temperature in Tm at a pressure of 17 GPa on phase transition from ambient pressure hcp-phase to α-Sm phase transition. In addition, measured equation of state (EOS) at low temperatures show anomalously low thermal expansion coefficients likely linked to magnetic transitions.

Current progress in the magnetism of rare-earth–hydrogen systems

We are reviewing recent progress obtained in the study of hydrogen interaction with magnetic structures in rare-earth metals, emphasizing the role of the ordering state of the H-sublattice. We shall present in particular: (1) the situation in the solid solutions of the heavy rare earths, α ∗ -RH x , and the efforts to relate the special quasi-unidimensional configuration of this phase (charge-density waves) to their modulated magnetism (spin-density waves) via the Fermi surface; (2) an assembly of all magnetic structures determined up to now in the heavy-RE dihydrides, β -RH(D) 2(+ x) , for a tentative comparison of the observed commensurate and/or incommensurate configurations; special mention will be made of the remarkably stable short-range ordered (SRO) magnetism always present in these systems; (3) the need for further (thorough) neutron scattering work on the magnetism in the insulating R-trihydrides, γ -RH(D) 3(− x) , in order to specify its mechanism in the absence of RKKY exchange interaction.

Quantization of electronic states in a rare-earth film: Gd/W(110)

A variety of distinct peaks occurs in photoemission spectra of ultrathin Gd on W(110) depending on the overlayer thickness, in particular a series of sharp peaks inside of a symmetry gap of the W band structure. Our phase-accumulation analysis assigns these structures to quantum-well states hitherto undetected in rare earths. This is of considerable importance since valence electrons mediate the magnetic coupling and determine the magnetic structure of rare-earth metals. As a first example of its impact, we demonstrate how the new quantum-well data help to resolve a current controversy concerning the nature of the Gd electronic structure.

Surface electronic structure of rare earth metals

Angle-resolved UV photoemission has been used to investigate the electronic structure of the (0001) surfaces of scandium, yttrium, praseodymium and gadolinium. Off-normal emission spectra were recorded with high angular resolution, enabling detailed mapping of the dispersion of valence band features. Yttrium and gadolinium show similar results to published data from Ho(0001), suggesting minimal 4f influence in the lanthanide bandstructures. Differences seen on praseodymium and scandium may be due to 4f derived states and surface states respectively.

Synchrotron X-ray scattering studies of rare earth metals

In recent years, synchrotron-based X-ray scattering studies of the rare earth metals have significantly enhanced our understanding of their structural, magnetic, and electronic properties. In this paper we review the results of high q-resolution X-ray magnetic scattering studies of the rare earth metals, focusing in particular on holmium. The observation of lock-in behavior and the discovery of additional charge scattering (arising from lattice modulations) have led to a new model of the magnetic structure of rare earth metals, based on the concept of “spin-slips”. More recently, studies have begun of the polarization and resonance properties of the X-ray magnetic cross-section. By measuring the degree of linear polarization, the orbital and spin contributions to the X-ray magnetic cross-section in holmium may be identified. When the incident X-ray energy is tuned through the L III absorption edge, a 50-fold resonant enhancement of the magnetic scattering and resonant second-, third-, and fourth-order harmonics are observed. This remarkable behavior may be explained on the basis of electric multipole transitions to 4f and 5d states, with the sensitivity to magnetization arising from exchange effects.

The electronic structure and band gaps in transition metal compounds

Abstract A many body theory recently introduced for describing the electronic structure of rare earth metals is applied to 3d transition metal compounds. The band gaps, their character and systematics, as well as various spectral distribution functions, are calculated and compared to recently obtained experimental data, for NiO and NiS.

Search of commensurate locking effects in the helical magnetic structures of Tb and Dy single crystals

We report a sensitive, high resolution, experimental method to investigate the possibility of small commensurate locking effects in helically modulated magnetic structures in rare earth metals, based on the fact that electrons moving along the c-axis strongly interact with the helical structure. By measuring a highly sensitive transport coefficient such as the temperature derivative of the c-axis electrical resistivity (dρ/d T) one may then see subtle effects related to the change in the turn angle ( w) with temperature. This new method has been used to investigate the antiferromagnetic structure of Tb and Dy single crystals. Sharp and rather localized anomalies (Δ ⪅ 0.2 K in Tb; Δ ⪅ 0.6 K in Dy) were observed in dρ/d T when the expected commensurate helical turn angles of 40°, 42° occur in Dy, and 20° in Tb.

Interactions of hydrogen in solution with magnetic structures in rare earth metals

The existence of a low temperature metastable α phase in the Tm-H and Er-H systems enables the interaction of hydrogen with magnetically ordered structures in these metals to be studied. The temperature dependences of the electrical conductivity and the magnetization were measured and, in combination with neutron diffraction data, the following results were obtained. The antiferromagnetic transition temperatures T N in α-TmH x and α- ErH x , the helicoidal transition temperature T H in α-ErH x , the paramagnetic Curie temperatures θ p and the effective magnetic moments μ p eff decrease with increasing x. This behaviour is explained in the framework of the Ruderman-Kittel-Kasuya-Yoshida model as the result of a diminution in the electronic density of states near the Fermi surface owing to the pumping of conduction electrons responsible for the exchange interaction by hydrogen (anion-like behaviour). The interaction with the ferromagnetically ordered structure is dominated by magnetoelastic effects due to crystal field anisotropy. Thus the addition of hydrogen to thulium produces a reduction in the Curie temperature T c and an increase in the saturation magnetic moment μ sat (0).This can be understood as a result of preferred magnetization in the c-axis-oriented antiphase structure of thulium (three spins up and four spins down) through crystal field distortion caused by the strain. In erbium, however, T C and T c' , (higher order harmonic) increase with increasing x and magnetic hardening of the specimens takes place, i.e. the polycrystalline ErH x specimens behave like single crystals of pure erbium oriented along the b axis. These results suggest that hydrogen interacts with the conical structure which exists in erbium below T C mainly by affecting the c axis component of the spins, thus transforming the sample into a magnetic monocrystal. The strong anisotropy of the magnetoelastic interaction of hydrogen suggests that the hydrogen atoms are in a uniaxially oriented configuration, probably in pairs along the c direction.

The influence of hexagonal anisotropy on the magnetic structure of antiferromagnetic rare earth metals and alloys

The effect of hexagonal base plane anisotropy on the antiferroniagnetic (AF) spiral spin structure of rare earth metals and alloys has been investigated. Minimization of the anisotropy energy is considered either by a reorientation of rigid coherent sections of the spiral or by a continuous modulation of the spiral periodicity. Both results indicate that when the spiral periodicity is commensurate with the hexagonal anisotropy the energy is greater than for spirals which are non-commensurate. The calculations predict that when the temperature is varied in the AF phase, the magnetic structure becomes unstable as a commensurate turn angle is approached, which may provide a qualitative explanation for the abrupt changes in the c-axis thermal expansion and temperature dependence of the elastic constant C 44 that have been observed experimentally in dysprosium and terbium-50% holmium. Further consequences of the spiral perturbation by hexagonal anisotropy are considered.

Ultrasonic study of magnetic structure of rare earth metals

Ultrasonic study of magnetic structure of rare earth metals

Book reviews

Abstract Abstract The Electronic Structure of Rare Earth Metals and Alloys: The Magnetic Heavy Rare Earths. By B. COQBLIN. (Academic Press (London), 1978.) [Pp. xivfG56, 315 illustrations.] f,29.50. Crystal Growth 1977. Edited by R. L. PARKER, A. A. CHERNOV, G. W. CULLEN and J. B. MULLIN. (North-Holland Publishing Company: Amsterdam, 1978.) [Pp. 6G2.1 Quantum Theory of Polymers. Edited by J. M. ANDRE, J. DELHALLE and J. LADIK. (Reidel: Dordrecht. Waves on Water of Variable Depth. Edited by D. G. PROVIS and R. RADOK. (Australian Academy of Sciences, Canberra and Springer-Verlag, Berlin, Heidelberg and New York.) [Pp. 231.1 $11.00, DM 24.80. Level: Postgraduate, specialist. Optimal Estimation in Approximation Theory. Edited by C. A. MICCHELLI and T. J. RIVLIX. (Plenum Publishing Co., 1977.) [Pp. x+300.] $35.40. Scope: Specialized mathematics. Level: Very advanced. Fiber Bundle Techniques in Gauge Theories. By W. DRECHSLER and M. E. MAYER. (Springer-Verlag, 1977.) [Pp. ix+248.] DM 24.80; $11.00. Inelastic Electron Tunnelling Spectroscopy. Edited by T. WOLFRAM. (Springer-Verlag, 1978.) [Pp. x+511.] DM 86; $4340. Scope: Review of a new technique. Level: For research workers new to the field. Theoretical and Computational Plasma Physics. (Selected Lectures from two Meetings at the International Centre for Theoretical Physics, Trieste, in March/April 1977.) (IAEA, Vienna, 1978.) [Pp. 515.1 $40.00. Scope: Applied mathematics and theoretical physics. Lcvcl: Postgraduate, research. Laser Induced Discharge Phenomena. By Yu. P. RAIZER. (Plenum, 1977.) [Pp. xivS366.1 Level: Third year undergraduate; $47.40. postgraduate. Scope: Research in physics and engineering. Rare Earths and Actinides, 1977. (Institute of Physics Conference Series No. 37). Edited by E22.00; W. D. CORNER and B. K. TANNER. $42.00. Scope: Conference Proceedings. Level: Research worker. (The Institute of Physics, 1978.) [Pp. xi+346.] Droplet Model of Atomic Nuclei By W. D. MYERS. (Plenum Press, 1978.) [Pp. xf150.1 $90.00. Scope: Nuclear Systematics. Level: Specialist. Contemporary Optics. By A. K. GHATAK and K. THYAGARAJAN. (Plenum Press, 1978). [Pp. x-+ 370.1 $39.00.

De Haas-van Alphen effect and Fermi surface of yttrium

The authors have found twelve de Haas-van Alphen effect frequencies, in the range 3*106 G to 108 G, for a single crystal of yttrium. The specimen, of resistance ratio 700, was purified by solid state electrotransport at the Centre for Materials Science, University of Birmingham. The frequencies have been identified with orbits on the Fermi surface proposed by Loucks (1966) from an APW bandstructure calculation. Agreement is generally good. In particular the 'webbing' feature which is thought to give rise to spiral magnetic structures in rare earth metals was found to exist, although the thickness is about 17% less than that given by Loucks. The results were all consistent with a spin-orbit coupling large enough to inhibit magnetic breakdown across the AHL face between the third and fourth Brillouin zones.

The structure of rare earth metals in the liquid state

Abstract The structure of liquid rare earth metals (So, La, Ce, Pr, Eu, Gd, Tb and Yb) have been systematically examined by X-ray diffraction at temperatures above their melting points. The structure factors of liquid La, Ce, Pr, Eu and Yb were temperature insensitive in the presently available experimental temperature range. In terms of the usual Fourier analysis, the atomic radial distribution functions were obtained from which interatomic distances and coordination numbers were estimated.

X-ray photoemission studies of the electronic structure of rare earth metals

X-ray photoemission (XPS) measurements are reported on evaporated films of the rare earth metals Eu, Gd, and Yb. For comparison additional measurements are reported on Ba. The results provide an unambiguous determination of the 4f energy levels. In Yb the spin–orbit splitting is also clearly resolved. The locations of the 4f levels below the Fermi level are determined to be 2.1 eV for Eu, 7.7 eV for Gd, and 1.4 eV and 2.7 eV for Yb all with an error of ± 0.4 eV. Es werden photoelektronenspektroskopische Messungen im Rontgenstrahlenbereich (XPS) fur aufgedampfte Schichten der Lanthaniden Eu, Gd und Yb sowie zum Vergleich auch fur Ba beschrieben. Die Ergebnisse ermoglichen eine eindeutige Bestimmung der 4f-Energieniveaus. Bei Yb ist zudem die Spin–Bahn-Aufspaltung deutlich aufgelost. Die Lage der 4f-Niveaus unterhalb des Ferminiveaus wurde bestimmt zu 2.1 eV fur Eu, 7,7 eV fur Gd und 1,4 und 2.7 eV fur Yb mit einem Fehler von ± 0.4 eV.