Polarized ³He spin filters for neutron scattering

Wangchun Chen, Thomas R. Gentile

Division 846, Physics Laboratory

Julie A. Borchers, Philippe Mangin, Kevin V. O’Donovan, Charles F. Majkrzak

NIST Center for Neutron Research, MSEL

Gordon Jones

Hamilton College

Polarized neutron scattering techniques are very important and powerful probes for the fundamental structures of magnetic materials. Polarized ³He spin filters, which are based on the large spin dependence of the absorption of neutrons by nuclear spin-polarized ³He, are playing a critical role in the polarized neutron scattering instrumentation because of their unique ability to polarize broadband neutron beams and analyze large solid angle scattered neutron beams.

The work presented describes two successful applications of ³He spin filters in neutron scattering. The first successful application is development of polarized neutron diffuse reflectometry using a polarized ³He analyzer in conjunction with a position sensitive detector. This work was carried out on the NG1 and AND-R polarized neutron reflectometers at the NIST Center for Neutron Research (NCNR).  In these experiments, we used patterned magnetic thin film samples that are prototypes for next-generation magnetic recording media. While some information regarding the magnetic characteristics of these samples can be gained from magnetic microscopy techniques, only neutron reflectivity can directly access buried layers and interfaces.  In a recent experiment we have achieved a record-high ³He polarization of 76 % on the neutron beam line. With this enhanced capability of the neutron reflectometer provided by ³He spin filters, we are now able to probe in-plane magnetic domain formation in patterned magnetic layers much more efficiently as compared to using a supermirror analyzer. The second successful application is development of a continuously operating compact neutron polarizer using a polarized ³He spin filter. This work was done at the Intense Pulsed Neutron Source single crystal diffractometer at Argonne National Laboratory. Polarizing ³He in-situ provides a constant neutron polarization and reduces the sensitivity to ³He relaxation mechanisms. These successful demonstrations have resulted in growing interest in using ³He neutron spin filters for other neutron scattering instruments at the NCNR such as trip-axis spectrometers.

The author name: Wangchun Chen

Mentor’s name: Thomas R. Gentile

Division 846, Physics Laboratory

B184 Bldg. 235, MS 8461

Phone: 301-975-6222

Email: wcchen@nist.gov

Not a Sigma Xi member

Category: Physics