SRC Users' Meeting - Synchrotron Radiation Center - University of ...
SRC Users' Meeting - Synchrotron Radiation Center - University of ... SRC Users' Meeting - Synchrotron Radiation Center - University of ...
PHOTOEMISSION STUDY OF USb AND UTe – 5f ELECTRONIC STRUCTURE AND MAGNETISM T. Durakiewicz 1, 2 , G. Lander 1 , C.G. Olson 3 , J.J. Joyce 1 , M. T. Butterfield 1 , E. Guziewicz 1, 4 , A.J. Arko 1 , J. L. Sarrao 1 , F. Wastin 4 , J. Rebizant 4 , K. Mattenberger 5 , and O. Vogt 5 1 Los Alamos National Laboratory, Los Alamos NM87545, USA; 2 Institute of Physics, UMCS Lublin, 20-031 Poland; 3 Ames Laboratory, Iowa State University, Ames IA, USA; 4 Institute of Physics, Polish Academy of Sciences, Warsaw, Poland; 4 European Commission, JRC, Institute of Transuranium Elements, Postfach 2340, D-76125 Karlsruhe, Germany; 5 Laboratorium fur Festkorperphysik, ETH, CH-8093 Zurich, Switzerland. USb and UTe single crystal compounds were investigated by angle-resolved photoelectron spectroscopy. Measurements were performed at the Synchrotron Radiation Center, Stoughton, WI, using the plane grating monochromator line, with an energy resolution of 20meV at 20eV light and an angular resolution of 1 degree. Uranium monoantimonide is an antiferromagnet with T N =214K. USb is an unusual monopnicitde, having a 3k magnetic ordering structure of type I, with the moments aligned towards the (111) direction [1]. Within the first eV below E F there are at least three well resolved peaks, A, B and C, positioned at approximately 55meV, 210meV and 610meV below E F , respectively. In previous work [2] peaks A and B were not resolved, due to lower energy resolution (50meV). In our ARPES study one may notice the following: (i) all three peaks are dispersive, with about 20meV dispersion for peak A, 50meV for peak B and about 100meV for peak C, (ii) the maximum photoemission intensity is seen around the X point, (iii) none of the peaks represent a band that crosses E F . The monotelluride UTe is a ferromagnet with T C =104K of a semi-metallic character. The -X ARPES reveals a structure within the first 1eV below E F composed of two bands, where the broader band B might be a superposition of more than one feature. Both bands seem to be relatively flat. Only a minor change in intensity is seen around the X point. Major changes in photoemission intensity are seen around the FM transition, where band A crosses EF at the transition. Since the FWHM of peak A is of the order of 200 meV, and it’s BE at low temperatures is about -55 meV, one cannot state that an actual gap is formed below the transition, as suggested in [3]. When compared with Np and Pu monoantimonides and monochalcogenides, a direct correlation between the binding energy of the peak bearing most of the 5f weight in the photoemission spectrum, magnetic moment and transition temperature may be seen within the series. Existence of such a correlation indicates the central role of 5f electrons in establishing the magnetic properties of these materials. Hybridization of the 5f electrons with the conduction band is found within the series and the level of localization is shown to increase from Sb to Te. The SRC is operated under Grant No. DMR-0084402. Work Supported by the US Department of Energy, Office of Science. References: [1] G.H. Lander and P. Burlet, Physica B 215, 7 (1995). [2] H. Kumigashira, T. Ito, A. Ashihara, H.D. Kim, H. Aoki, T. Suzuki, H. Yamgami and T. Takhashi, Phys. Rev. B 61, 15707 (2000). [3] B. Reihl, N. Martensson and O. Vogt, J. Appl. Phys. 53, 2008 (1982).
FIELD IONIZATION OF CH 3 I IN SUPERCRITICAL AR C. M. Evans 1 and G. L. Findley 2 1 Department of Chemistry and Biochemistry, Queens College – CUNY, 65-30 Kissena Blvd, Flushing, NY 11367 2 Department of Chemistry, University of Louisiana at Monroe, Monroe, LA 71209 Supercritical fluids have recently been shown to improve rates and modify product ratios of chemical reactions, to vary chemical shifts in NMR, and to alter lifetimes and energies of molecular vibrational states. However, the detailed nature of the molecule (i.e., dopant)/fluid (i.e., perturber) interactions that lead to these effects is not well understood. In recent studies of the density dependence of solvatochromic shifts of vibrational and UV-visible absorption bands, an increase in the energy shift near the critical density along the critical isotherm of the perturber was observed (cf. Fig. 1). In measurements of the field ionization of high-n CH 3 I Rydberg states in supercritical argon, we observed a decrease in the shift near the critical density along the critical isotherm (cf. Fig. 2). Such a dramatic difference in behavior is striking. The densitydependent shift of the dopant ionization energy in dense media can be written as a sum of contributions, = w 0 (P) + V 0 (P), where w 0 is the shift due to the average polarization of the perturber by the ionic core, V 0 is the quasi-free electron energy in the perturbing medium and P is the perturber number density. Our preliminary analysis suggests that while w 0 shifts in a manner similar to the vibrational and UV-visible band shifts, V 0 does not. Thus, the difference in behavior between the shift of high-n Rydberg states and of vibrational (or UV-visible) absorption bands is due to the interaction of the quasi-free electron with the perturbing medium. This work was conducted at SRC (NSF DMR-0084402) and was supported by a grant from the Louisiana Board of Regents Support Fund (LEQSF (1997-00)-RD-A-14). 1996 0.0 1994 -0.2 line position (cm ) -1 1992 1990 1988 (eV) -0.4 -0.6 1986 -0.8 1984 0 2 4 6 8 10 12 14 16 18 density (mol/L) Fig. 1. Infrared absorption line peak position of the T 1u asymmetric CO stretching mode of W(CO) 6 in CO 2 vs CO 2 density at (!) the critical temperature of 33C and () 50C. The lines provide a visual aid. (Modified from R.S. Urdahl, D. J. Myers, K. D. Rector, P. H. Davis, B. J. Cherayil and M. D. Fayer, J. Chem. Phys 107, 3747 (1997).) -1.0 0 5 10 15 Ar (10 21 cm -3 ) Fig. 2. Ionization potential of CH 3 I in argon plotted as a function of argon number density Ar. () -114C; () -118C; () various lower temperatures other than the critical temperature; () the critical temperature of -122C. The lines provide a visual aid. (C. M. Evans and G. L. Findley, to be published.) 20 25
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PHOTOEMISSION STUDY OF USb AND UTe – 5f ELECTRONIC<br />
STRUCTURE AND MAGNETISM<br />
T. Durakiewicz 1, 2 , G. Lander 1 , C.G. Olson 3 , J.J. Joyce 1 , M. T. Butterfield 1 , E. Guziewicz 1, 4 ,<br />
A.J. Arko 1 , J. L. Sarrao 1 , F. Wastin 4 , J. Rebizant 4 , K. Mattenberger 5 , and O. Vogt 5<br />
1 Los Alamos National Laboratory, Los Alamos NM87545, USA; 2 Institute <strong>of</strong> Physics, UMCS<br />
Lublin, 20-031 Poland; 3 Ames Laboratory, Iowa State <strong>University</strong>, Ames IA, USA; 4 Institute <strong>of</strong><br />
Physics, Polish Academy <strong>of</strong> Sciences, Warsaw, Poland; 4 European Commission, JRC, Institute<br />
<strong>of</strong> Transuranium Elements, Postfach 2340, D-76125 Karlsruhe, Germany; 5 Laboratorium fur<br />
Festkorperphysik, ETH, CH-8093 Zurich, Switzerland.<br />
USb and UTe single crystal compounds were investigated by angle-resolved<br />
photoelectron spectroscopy. Measurements were performed at the <strong>Synchrotron</strong> <strong>Radiation</strong> <strong>Center</strong>,<br />
Stoughton, WI, using the plane grating monochromator line, with an energy resolution <strong>of</strong> 20meV<br />
at 20eV light and an angular resolution <strong>of</strong> 1 degree.<br />
Uranium monoantimonide is an antiferromagnet with T N =214K. USb is an unusual<br />
monopnicitde, having a 3k magnetic ordering structure <strong>of</strong> type I, with the moments aligned<br />
towards the (111) direction [1]. Within the first eV below E F there are at least three well resolved<br />
peaks, A, B and C, positioned at approximately 55meV, 210meV and 610meV below E F ,<br />
respectively. In previous work [2] peaks A and B were not resolved, due to lower energy<br />
resolution (50meV). In our ARPES study one may notice the following: (i) all three peaks are<br />
dispersive, with about 20meV dispersion for peak A, 50meV for peak B and about 100meV for<br />
peak C, (ii) the maximum photoemission intensity is seen around the X point, (iii) none <strong>of</strong> the<br />
peaks represent a band that crosses E F .<br />
The monotelluride UTe is a ferromagnet with T C =104K <strong>of</strong> a semi-metallic character. The<br />
-X ARPES reveals a structure within the first 1eV below E F composed <strong>of</strong> two bands, where the<br />
broader band B might be a superposition <strong>of</strong> more than one feature. Both bands seem to be<br />
relatively flat. Only a minor change in intensity is seen around the X point. Major changes in<br />
photoemission intensity are seen around the FM transition, where band A crosses EF at the<br />
transition. Since the FWHM <strong>of</strong> peak A is <strong>of</strong> the order <strong>of</strong> 200 meV, and it’s BE at low<br />
temperatures is about -55 meV, one cannot state that an actual gap is formed below the<br />
transition, as suggested in [3].<br />
When compared with Np and Pu monoantimonides and monochalcogenides, a direct<br />
correlation between the binding energy <strong>of</strong> the peak bearing most <strong>of</strong> the 5f weight in the<br />
photoemission spectrum, magnetic moment and transition temperature may be seen within the<br />
series. Existence <strong>of</strong> such a correlation indicates the central role <strong>of</strong> 5f electrons in establishing the<br />
magnetic properties <strong>of</strong> these materials. Hybridization <strong>of</strong> the 5f electrons with the conduction<br />
band is found within the series and the level <strong>of</strong> localization is shown to increase from Sb to Te.<br />
The <strong>SRC</strong> is operated under Grant No. DMR-0084402. Work Supported by the US<br />
Department <strong>of</strong> Energy, Office <strong>of</strong> Science.<br />
References:<br />
[1] G.H. Lander and P. Burlet, Physica B 215, 7 (1995).<br />
[2] H. Kumigashira, T. Ito, A. Ashihara, H.D. Kim, H. Aoki, T. Suzuki, H. Yamgami and T.<br />
Takhashi, Phys. Rev. B 61, 15707 (2000).<br />
[3] B. Reihl, N. Martensson and O. Vogt, J. Appl. Phys. 53, 2008 (1982).
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