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Description: Angle-resolved photoemission energy distributions (PED's) were obtained from valence bands of MnF{sub 2} single crystals using AlK{alpha} radiation. A pronounced variation in the PED's was observed as the electron take-off angle was varied relative to the crystalline axes, for the (111) crystal face. The observed variation is attributed to the t{sub 2g} and e{sub g} symmetry properties of the manganese 3d initial state wave functions and is well described by an angle-dependent transition-matrix model. The results are in good agreement with the multi-configurational Hartree-Fock calculations of Viinikka and Bagus.
Date: September 1, 1977
Creator: Sherwood, P.M.A.; McFeely, F.R.; Kowalczyk, S.P. & Shirley, D.A.
Partner: UNT Libraries Government Documents Department

Neutron study of fracton excitations in percolating antiferromagnets

Description: The authors report the results of an inelastic neutron scattering experiment on nearly-percolating Heisenberg antiferromagnets (RbMn{sub c}Mg{sub 1{minus}o}F{sub 3}), in which the Mn concentrations (C = 0.31, 0.34 and 0.39) are very close to the percolation threshold (c{sub p} = 0.312). A broad peak superimposed on Ising-cluster excitations was observed throughout the Brillouin zone. The intensity of a broad peak increased on approaching the percolation threshold. The origin of this broad peak is attributed to the excitation of fractons in a percolating network.
Date: June 27, 1997
Creator: Ikeda, H.; Takahashi, M.; Fernandez-Baca, J.A. & Nicklow, R.M.
Partner: UNT Libraries Government Documents Department

Experimental studies of critical behavior in systems with quenched disorder. Progress report 1995--1996

Description: During the past year the author finished a variety of projects and started new projects with a major focus on randomness and frustration in magnetic systems. A major achievement has been to do critical behavior measurements on a random-field system Fe{sub 0.91}Zn{sub 0.09}F{sub 2}. Experimental collaborations are ongoing with the Marinelli group from Rome. Earlier measurements of the dynamics near phase transitions to a Heisenberg system RbMnF{sub 3} were extended. The author is collaborating with Montenegro from Recife, Brazil, on the behavior of antiferromagnets near to the percolation threshold. Specific heat measurements were concluded at UCSC on the frustrated metallic system UNi{sub 4}B. The antiferromagnetic interactions are frustrated on a nearly triangular magnetic sublattice. It was shown that the critical behavior was suggestive of Heisenberg universality.
Date: November 1, 1996
Creator: Belanger, D.P.
Partner: UNT Libraries Government Documents Department

m/sup +/SR studies on pure MnF/sub 2/ and site-diluted (Mn/sub 0. 5/Zn/sub 0. 5/)F/sub 2/

Description: Positive muon spin rotation and relaxation measurements have been carried out on the antiferromagnets, pure MnF/sub 2/ and site-diluted (Mn/sub 0.5/Zn/sub 0.5/)F/sub 2/, above and below the Neel temperature T/sub N/ using single-crystal specimens. Two different muon signals have been found in the pure MnF/sub 2/; with the precession frequency nu/sub A/ = 1.3 GHz for the site A and nu/sub B/ = 152 MHz for the site B measured in zero external magnetic field at T = 5 K. We propose a picture that the signal from the A site represents the ''muonium'' state, and discuss the characteristic features of muonium in magnetic materials. The spin relaxation rate 1/T/sub 1/, measured in zero external field, decreases rapidly with decreasing temperature below T/sub N/. The mechanism of the spin relaxation above T/sub N/ is explained by the exchange fluctuations of the Mn moments, while below T/sub N/ by the Raman scattering of spin waves. At the same normalized temperature T/T/sub N/, 1/T/sub 1/ observed in the diluted (Mn/sub 0.5/Zn/sub 0.5/)F/sub 2/ is significantly larger than that in the pure MnF/sub 2/ below T/sub N/. The difference between the pure and diluted systems is related to the large spectral weight of low-energy magnons in (Mn/sub 0.5/Zn/sub 0.5/)F/sub 2/ found by neutron scattering.
Date: January 1, 1986
Creator: Uemura, Y.J.; Keitel, R.; Senba, M.; Kiefl, R.F.; Kreitzman, S.R.; Noakes, D.R. et al.
Partner: UNT Libraries Government Documents Department

Explosive generation of high magnetic fields in large volumes and solid state applications

Description: Various methods of producing ultra-high magnetic fields by explosive flux compression are described. A survey is made of the kinds of high magnetic field solid state data obtained in such fields by various groups. Preliminary results are given for the magnetic phase boundary that separates the spin-flop and paramagnetic regions of MnF/sub 2/.
Date: January 1, 1980
Creator: Fowler, C.M.; Caird, R.S.; Erickson, D.J.; Freeman, B.L. & Garn, W.B.
Partner: UNT Libraries Government Documents Department

High resolution near edge x-ray spectroscopy

Description: A technique to suppress the core-hole lifetime broadening in near- edge x-ray spectroscopy is presented. A simple theoretical explanation based on total energy conservation in the fluorescence process is given to explain the improved resolution. The experimental arrangement is shown together with an application to the L[sub III] edge of dysprosium. Furthermore, the application of high-resolution fluorescence spectroscopy in the study of magnetism is presented. The spin-resolved absorption spectra from MnF[sub 2] are shown as an example.
Date: January 1, 1992
Creator: Haemaelaeinen, K.; Siddons, D.P.; Berman, L.E.; Kao, C.C. & Hastings, J.B.
Partner: UNT Libraries Government Documents Department

Light scattering studies of solids and atomic vapors

Description: The general technique of light scattering and luminescence was used to study the properties of a number of material systems. First, multi-phonon resonant Raman scattering up to four phonons in GaSe and one- and two-phonon resonant Raman scattering in the mixed GaS/sub x/Se/sub 1-x/ crystals with x < or = 0.23 were investigated. Second, the observation of one-phonon resonant Raman scattering in HfS/sub 2/ is reported. The result is used to determine the position of the direct gap of HfS/sub 2/. Third, the first observation of the ..pi..-polarized one-magnon luminescence sideband of the /sup 4/T/sub lg/ (/sup 4/G) ..-->.. /sup 6/A/sub lg/(/sup 6/S) excitonic transition in antiferromagnetic MnF/sub 2/ is presented. An effective temperature of the crystal is deduced from the simultaneously observed anti-Stokes sideband emission. Multi-magnon (< or = 7) excitonic luminescence sidebands were also observed in MnF/sub 2/, KMnF/sub 2/, and RbMnF/sub 3/ using pulsed excitation and detection. A simple model based on two-ion local exchange is proposed to explain the results qualitatively. Fourth, the first observation of two-magnon resonant Raman scattering in MnF/sub 2/ around the magnon sidebands is reported. A simple theoretical description explains the experimental observations. Fifth, a detailed theory of exciton-exciton interaction in MnF/sub 2/ is developed to explain and to predict the experimental results on two-exciton absorption, high level excitation, and exciton--exciton scattering. Sixth, Brillouin scattering was used to obtain the five independent elastic constants of the layered compound GaSe. The results show clear elastic anisotropy of the crystal. Resonant Brillouin scattering near the absorption edge was also studied, but no resonant enhancement was found. Seventh, two-photon parametric scattering in sodium vapor was studied. Phase matching angles and scattering cross sections are calculated for a given set of experimental conditions.
Date: September 1, 1978
Creator: Chiang, T.C.
Partner: UNT Libraries Government Documents Department

X-ray absorption spectroscopy beyond the core-hole lifetime

Description: A new technique to overcome the core-hole lifetime broadening in x-ray absorption spectroscopy is presented. It utilizes a high resolution fluorescence spectrometer which can be used to analyze the fluorescence photon energy with better resolution than the natural lifetime width. Furthermore, the high resolution spectrometer can also be used to select the final state in the fluorescence process which can offer spin selectivity even without long range magnetic order in the sample.
Date: January 1, 1992
Creator: Haemaelaeinen, K.; Hastings, J.B.; Siddons, D.P. & Berman, L.
Partner: UNT Libraries Government Documents Department

Application of soft x-ray appearance potential spectroscopy to light lanthanides, 4d transition metals, and insulators

Description: Evaporated films of La, Ce, Yb, Y, Ag--Mn(5 percent), KCl, MnF$sub 2$, CsCl and LaF$sub 3$ were studied using the soft x-ray appearance potential spectroscopy (SXAPS) technique. Studies were also made of bulk polycrystalline samples of Y, Zr, Nb, and Mo. The results are discussed in terms of existing SXAPS theories. Several similarities between soft x-ray absorption (SXA) data and the SXAPS results are discussed, and it is shown that the SXA data can aid in the interpretation of SXAPS spectra when using the well-known self-convolution model. In this approximation the absorption coefficient, $alpha$(E), is substituted for the density of states, N(E-E/sub c/) $Yields$ $alpha$(E). For more localized excitations, a convolution of $alpha$(E) with bremsstrahlung isochromat data, based on Wendin&#x27;s two density of states formalism is used to predict SNAPS results. (auth)
Date: October 1, 1975
Creator: Smith, R. J.
Partner: UNT Libraries Government Documents Department