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Summary: Magnetic and crystallographic order in *manganese
A. C. Lawson, Allen C. Larson, M. C. Aronson,`) S. Johnson,b) Z. Fisk, P. C. Canfield,c)
J. D. Thompson, and R. B. Von-Dreele
Los Alanzos National Laboratory, Los Alamos, New Mexico 87.545
We have made time-of-flight neutron diffraction measurementson a-manganesemetal. Powder
diffraction measurementswere madeat 14 temperaturesbetween15 and 305 K, and single crystal
measurementsweremadeat 15 and300 K. We found that_thecrystal structureof o-Mn is tetragonal
below its N&e1point of 100 K, with crystal symmetryI42m and magnetic(Shubnikov)symmetry
P,a21c. In agreementwith the earlierresultsof Yamadaet al., thereare six independentmagnetic
atoms,andwe found that their momentsareweakly temperaturedependent.The onsetof magnetic
order causesslight changesin the atomic positionsand in the averageatomic elastic constant.
I. INTRODUCTlON
a-manganesehas a surprisingly complex cubic crystal,
structurewith 58 atoms per body-centeredcell.' The com-
plexity is surprising, becausemost elements have simple
structures.In the caseof Mn, the complexity is thought to
arise from an instability of the 3d electronshell that gives
rise to the formation of "self-intermetallic" compounds.In
other words, elementalMn is actually an intermetallic com-
pound betweenMn atoms in different electronic configura-
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