#
# arev:/usr/local/unicat/unireq/beamreq/req00045.txt
# UNICAT Member Beam Time Request  #45

# created Wed Feb 24 10:36:00 CST 1999
#

days:
	5-7

description:
	We propose to use conventional and resonant magnetic x-ray scattering
	to study the metal-insulator phase transition in Cd2Os2O7.  Cd2Os2O7
	exhibits the magnetically frustrated pyrochlore crystal structure
	(space group Fd3m and lattice constant a=10.17A at room temperature)
	which consists of two interpenetrating sublattices of corner
	sharing tetrahedra.  Transport measurements [1,2] have shown that this
	compound undergoes a sharp metal-insulator transition at 226 K with no
	apparent change in crystal symmetry at the transition and only a small
	change in lattice constant.  Magnetic susceptibility suggests
	antiferromagnetic order which accompanies the metal-insulator transition
	and a very small ferromagnetic component (10^-3 Bohr Mag./F.U.) which
	may be due to spin canting.
	The presence of Cd in the compound makes neutron scattering studies
	of the magnetic order extremely difficult.  For this reason, coupled
	with the easily attainable energies of the Os L edges (LI=12.9680 keV,
	LII=12.3850 keV, LIII=10.8709 keV), resonant magnetic x-ray scattering
	should provide an invaluable tool in the characterization of the magnetic
	order in this novel compound.
	
	We presently have several single crystals (approximate dimensions on
	the order of 1mm) which are suitable for magnetic x-ray diffraction.
	The 226 K transition temperature allows the experiment to easily
	be performed in a DISPLEX.  We plan to measure the crystal lattice
	constants carefully both above and below the metal-insulator transition
	and use resonant magnetic x-ray scattering to characterize the associated
	antiferromagnetic order.
	
	References
	
	[1] A.W. Sleight et. al. Solid State Comm. 14, 357 (1974).
	
	[2] D. Mandrus et. al. unpublished.
	
	

equipment+required:
	displex

experiment:
	X-Ray Scattering Study of Cd2Os2O7

hazards:
	

name:
	Stephen E. Nagler (ORNL)

new+request:
	on

nonmembers:
	COMMENT:
	The proposed experiment is being discussed with Ben Larson
	at ORNL - The collaborators are Stephen E. Nagler and 
	Mark D. Lumsden both from ORNL.

station:
	33ID-D

unacceptable+dates:
	Before April 5th



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