Nuclear Polarization Dependence of Coherent Neutron Scattering from Holmium

Abstract

Neutron diffraction measurements with unpolarized neutrons have been made on a single crystal of Ho in the temperature range 4.2 K to 0.4 K with the aim of studying the change in coherent scattering produced by the h.f.s. induced polarization of the Ho nuclear spins. It was found that the magnetic satellite reflections decrease linearly with nuclear polarization, but that no effect could be seen on the ordinary hexagonal reflections. The incoherent scattering amplitude was found to be binc=−0.086±.008×10−12cm. The magnetic structure reported by Koehler et.al. was confirmed except for the spin bunching parameter δ. We find δ=8.3° where Koehler finds δ=5.8°. Since δ=0° represents complete bunching, our measurement suggests that the magnetic anisotropy does not affect the magnetic structure as much as Koehler suggests. Using the Ho coherent scattering amplitude bcoh=0.85×10−12cm we find that the two compound nucleus scattering amplitudes are b+=+0.70±.04×10−12cm and b_=+1.04±.04×10−12cm.