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Magnetism in the actinides: the role of neutron scattering

Description: Neutron scattering has played a crucial and unique role of elucidating the magnetism in actinide compounds. Examples are given of elastic scattering to determine magnetic structures, measure spatial correlations in the critical regime, and magnetic form factors, and of inelastic scattering to measure the (often elusive) spin excitations. Some future directions will be discussed.
Date: January 1, 1982
Creator: Lander, G.H.
Partner: UNT Libraries Government Documents Department

Neutron scattering studies of amorphous Invar alloys

Description: This paper reviews recent inelastic neutron scattering experiments performed to study the spin dynamics of two amorphous Invar systems: Fe/sub 100-x/B/sub x/ and Fe/sub 90-x/Ni/sub x/Zr/sub 10/. As in crystalline Invar Fe/sub 65/Ni/sub 35/ and Fe/sub 3/Pt, the excitation of conventional long-wavelength spin waves in these amorphous systems cannot account for the relatively rapid change of their magnetization with temperature. These results are discussed in terms of additional low-lying excitations which apparently have a density of states similar to the spin waves.
Date: January 1, 1989
Creator: Fernandez-Baca, J.A.
Partner: UNT Libraries Government Documents Department

The time evolution of the first order magnetic phase transition in Dy-4%Y alloy

Description: The first order magnetic transition of spiral to ferromagnetic structure of Dy-4%Y alloy has been investigated by means of Synchrotron X-ray diffraction. The development of the ferromagnetic phase could be studied by X-ray diffraction measurement for the observation of the hexagonal to orthorhombic crystal distortion accompanying the first order magnetic transition. Below {Tc}, the ferromagnetic and spiral phases coexist and the development of the ferromagnetic phase exhibits a time dependent behaviour and is proportional to logt except in the early stage of the phase transition. 6 refs., 2 figs.
Date: January 1, 1991
Creator: Tajima, K. (Keio Univ., Yokohama (Japan). Dept. of Physics); Akimitsu, J. (Aoyama Gakuin Univ., Tokyo (Japan). Dept. of Physics); Akimitsu, M. (Shibaura Inst. of Tech., Tokyo (Japan)); Rebelsky, L.; Gruebel, G. & Shirane, G. (Brookhaven National Lab., Upton, NY (USA))
Partner: UNT Libraries Government Documents Department

(The relationship between microstructure and magnetic properties in high-energy permanent magnets characterized by polytwinned structures)

Description: This report summarizes the results of a study of the relationship between microstructure and magnetic properties in a unique genre of ferromagnetic material characterized by a polysynthetically twinned structure which arises during solid state transformation. These results stem from the work over a period of approximately 27 months of a nominal 3 year grant period. The report also contains a proposal to extend the research project for an additional 3 years. The polytwinned structures produce an inhomogeneous magnetic medium in which the easy axis of magnetization varies quasi-periodically giving rise to special domain configurations which are expected to markedly influence the mechanism of magnetization reversal and hysteresis behavior of these materials in bulk or thin films. The extraordinary permanent magnet properties exhibited by the well-known Co-Pt alloys as well as the Fe-Pt and Fe-Pd systems near the equiatomic composition derive from the formation of a polytwinned microstructure.
Date: January 1, 1992
Partner: UNT Libraries Government Documents Department

Antiferromagnetic spin fluctuations and the heavy fermion system UPt/sub 3/

Description: We review the results of inelastic polarized and unpolarized magnetic neutron scattering measurements on the heavy fermion superconductor UPt/sub 3/. Below T/sub chi/ = 18K, we find evidence for antiferromagnetic spin fluctuations with a modulation vector along the c-axis of the hexagonal lattice. This contradicts the analogy often made between UPt/sub 3/ and liquid /sup 3/He, and may have important consequences for the pairing mechanism responsible for superconductivity in this system.
Date: January 1, 1986
Creator: Goldman, A.I.; Shirane, G.; Aeppli, G.; Bucher, E. & Hufnagl, J.
Partner: UNT Libraries Government Documents Department

Structural distortion in RPt sub 2 Sn sub 2 compounds (R = rare earth)

Description: CeM{sub 2}X{sub 2} compounds (M-transition metals, X = Si, Ge, Sn) exhibit very exotic properties such as intermediate valence state, heavy fermion, magnetism, and superconductivity. Most of them crystallize in the ThCr{sub 2}Si{sub 2} type structure (14/nmm) while a few adopt the CeBe{sub 2}Ge{sub 2} primitive one (P4/nmmm). Among these compounds, CePt{sub 2}Sn{sub 2} has the heaviest known specific heat coefficient ({gamma} = 3.5 J/mol-K{sup 2}) and orders antiferromagnetically at T{sub N} = 0.88 K. Samples of CePt{sub 2}Sn{sub 2}, Ce{sub 0.e}La{sub 0.2}Pt{sub 2}Sn{sub 2}, and LaPt{sub 2}Sn{sub 2} have been studied by X-ray powder diffraction experiments including Rietveld calculations before and after annealing. As-cast samples can be indexed in the tetragonal primitive cell; however, re- examination of annealed samples (1 3 days at 800{degrees}C and 3 weeks at 700{degrees}C) reveals a monoclinic distortion of the lattice. Such a distortion has already been observed for CeNi{sub 2}Sn{sub 2}. Furthermore, our diffraction patterns show evidence for superlattice lines at twice the unit cell parameters, which was verified by transmission electron microscopy. Microprobes analysis on these samples show that the Pt sublattice is slightly substoichiometric (97.5%). Thus strains due to large atomic radii and ordering of Pt vacancies could be responsible for the monoclinic distortion and superlattice lines. 13 refs., 3 figs., 1 tab.
Date: January 1, 1991
Creator: Latroche, M.; Selsane, M.; Godart, C.; Schiffmacher, G. (Centre National de la Recherche Scientifique (CNRS), 92 - Meudon-Bellevue (France)); Beyerman, W.P. & Thompson, J.D. (Los Alamos National Lab., NM (USA))
Partner: UNT Libraries Government Documents Department

Neutron scattering studies of heavy Fermions. [CeAl/sub 3/, UBe/sub 13/, CeCu/sub 2/Si/sub 2/, CeCu/sub 6/, ThBe/sub 13/, UPt/sub 3/, U/sub 2/Zn/sub 17/]

Description: Heavy Fermions are f electron materials characterized by a large linear term in the low temperature specific heat and a large magnetic susceptibility at low temperatures. This implies that there is a narrow peak in the f electron density of states at the Fermi energy. Typical examples are CeAl/sub 3/, UBe/sub 13/, CeCu/sub 2/Si/sub 2/, CeCu/sub 6/, U/sub 2/Zn/sub 17/ and UPt/sub 3/. Neutron scattering measurements can play an important role in understanding the magnetic interactions in these systems. Measurements of the form reveal details about the nature of the wave functions. Inelastic scattering studies gives information about the energy scale of the spin fluctuations and the narrow f-resonance. Such measurements on the above systems are reviewed with the goal of establishing systematics between the information obtained in neutron studies and that from bulk measurements.
Date: January 1, 1985
Creator: Shapiro, S.M.
Partner: UNT Libraries Government Documents Department