Absolute measurement of the critical scattering cross section in cobalt Page: 1 of 9
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1
INTRODUCTION
From the angular distribution of neutrons critic-
ally scattered from magnetic systems, considerable
informaion can be obtained regarding the long range
spin co-relations which develop near the critical point.
In the quasi-static limits the scattered neutron inten-
sity is directly proportional to the wave-vector-depend-
ent susceptibility x(q) which in the Orstein-Zernike
approximation has the simple formX(q)= Xo
2 2
rl(Kl+q )2 -
XO=(gp ) S(S+l)/3kBT(1)
for small scattering vectors q. X(q) is related to
the spin pair correlation function y(r) by Fourier
inversion, which, from Eq.(1), gives the well-known
asymptotic dependencey(r)a 1 e-1r
r(2)
for large distances r. The correlation range of the
spin fluctuations, 9=Kl 1, is obtained directly from
the width of the Lorentzian shaped critical scattering
and has been extensively investigated in numerous
materials. However, to determine the parameter ri,
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ABSOLUTE MEASUREMENT OF THE CRITICAL SCATTERING CROSS SECTION IN COBALT
C. J. Glinka*t and V. J. Minkiewicz*1# 6. 7 '.Z'9- -9
University of Maryland, College Park, Maryland 20742
and
L. Passella*
Brookhaven National Laboratory, Upton, New York 11973
ABSTRACT
Small-angle neutron scattering techniques have
been used to study the angular distribution; of the
critical scattering from cobalt above T . These mea-
surements have been put on an absolute scale by cali-
brating the critical scattering directly against the
nuclear incoherent scattering from cobalt. In this
way the interaction range rl, which appears in the
classical and modified Ornstein-Zernike expressions
for the asymptotic form of the spin pair correlation
function and is related to the strength of the spin
correlations, has been determined. We obtain ri/a =
0.46 0.03 for the ratio of the interaction range to
the nearest-neighbor distance in cobalt. This result
is in good agreement with theoretical predictions.
Lack of agreement among previous determinations of
the ratio rl/a made in iron failed to provide a defini-
tive comparison with theory.ec e a 3
Z7 ZoE
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Glinka, C. J.; Minkiewicz, V. J. & Passell, L. Absolute measurement of the critical scattering cross section in cobalt, article, January 1, 1975; Upton, New York. (https://digital.library.unt.edu/ark:/67531/metadc866365/m1/1/?rotate=90: accessed July 15, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.