Neutron Scattering

An experimental verification of this new technique is shown in Fig . 4 .19 . Here, the
magnetic (100) Bragg peak of an antiferromagnetic MnF 2 single crystal can produce such
a 90 degree rotation of the polarisation . The ordered magnetic structure is collinear, wich
spins pointing into c-direction, which is oriented in between the x and z direction of the
instrument . Varying the field strength of the y-coil, the initial polarisation at the sample
precesses perpendicular to y leading to a final polarisation as shown in Fig . 4 .19 .
neutron polarization analysis
Pxy from P-precession in xz-plane
Blly
M11C11Q
2 2 .5 3 3 .5 4
l y [A]
Figure 4 .19 : Measurement of off-diagonal elements of the polarisation tensor using the
(100) Bragg scattering of antiferromagnetic MnF 2 , in which the magnetic moments are
aligned parallel to the c-axis . The precession angle in xz-plane of the initial polarisation
depends on the field By (x I y ), and only neutrons with final polarisation Py are detected .
Appendix
Units :
magnetic field H :
Oersted Ampere/meter (SI) = 47r x 10-3
(cgs)
magnetic induction B = ,uo uH, po = 1.2566 x 10-sm kg C-2 (=1 in cgs-units) :
Tesla (SI) = kg / (sec2 Ampere) = 10 4 Gauss (cgs)
For cgs-units and vacuum (N = 1), H in Oe corresponds to B in Gauss .
Earth magnetic field : ~ 15 A/m ~ 0 .19 Oe .
4-24