Abstract
We present the status of development of a novel neutron spin filter based on the strong spin dependence of the neutron scattering on protons. Using photo-excited triplet states for the dynamic nuclear polarization (DNP) process, proton polarization values of 80% can now be achieved in pentacene doped single crystals of naphthalene at a field of 0.36 T in a simple helium flow cryostat. Careful sample preparation lead to extremely long polarization decay times under moderate conditions that allowed us to develop a transportable device. The filter is polarized in the lab under well controlled conditions and is then transferred to the neutron beam line where it can be operated during several days with almost constant polarization while requiring only a minimum of equipment. We describe briefly the main features of the spin filter and its use as a spin analyzer in a small-angle neutron scattering (SANS) experiment probing the magnetic structure of a nanocrystalline soft magnetic material. Furthermore the procedure for performing the background and spin leakage corrections of the neutron data is outlined in detail.
Highlights
In their classical experimental study Moon, Riste and Koehler [1] introduced the one dimensional polarization analysis and demonstrated the polarization dependence of nuclear and magnetic scattering, which allows the unambiguous separation of magnetic scattering from nuclear scattering
This experiment demonstrates that our neutron spin filter, though presently still limited in the flipping ratio to below 5, can reveal the small spin-flip signal of a magnetic scattering
Outlook and conclusion We have demonstrated that a neutron spin filter based on protons polarized by triplet dynamic nuclear polarization (DNP) is perfectly suited to be used as spin analyzer in small-angle neutron scattering (SANS) experiments investigating magnetic properties of nanocrystalline materials, which so far have been be studied using cells of polarized 3He gas
Summary
In their classical experimental study Moon, Riste and Koehler [1] introduced the one dimensional polarization analysis and demonstrated the polarization dependence of nuclear and magnetic scattering, which allows the unambiguous separation of magnetic scattering from nuclear scattering. By a polarization analysis of the scattered neutrons, measuring the so called spin-flip process, which is free of coherent nuclear SANS and purely magnetic, one gets access to the magnetic scattering vector (Halpern-Johnson vector) [2] perpendicular to the neutron polarization. This information is crucial for the understanding of the magnetic response of magnetic materials in intermediate non saturating fields [3], as well as the unique spin structure of exotic non-collinear magnetic phases e.g. skyrmions [4].
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