Bulk magnetic structure studies using polarized epithermal neutrons

Abstract

Parity violating effects in the nucleus are normally very small, but in certain compound nuclear resonances such effects are enhanced to several percent, as in the 0.734 eV p-wave resonance in ¹³⁹La. We have used this enhanced parity violation to measure the depolarization of neutrons traversing a thick single crystal of ferromagnetic holmium.

The depolarization was dependent on the relative orientation of the neutron polarization and the holmium c crystalline axis. The effect was explained in terms of neutron precession in an array of highly correlated domains magnetized in the c axis direction. The results show the high degree of correlation of magnetic domains in the single crystal and demonstrate the usefulness of epithermal neutrons in measuring magnetic properties of thick crystals. The use of other parity violating resonances should allow polarization analysis of neutrons over a range of neutron energies.