College Park, Maryland      June 6 - 10 , 2004

ACNS Home Meeting Announcement Committees and Contacts Registration Abstract Submission Travel Reimbursement Dates to Remember

T2-C1 (1:30 PM): Spin-analyzed diffuse scattering measurements of magnetic thin films with a ³He analyzer and a position-sensitive detector

W. C. Chen (National Institute of Standards and Technology; Indiana University), K.V. O'Donovan (NIST Center for Neutron Research; University of Maryland, College Park), J.A. Borchers, C.F. Majkrzak, T.R. Gentile (National Institute of Standards and Technology)

Polarized ³He gas, produced by optical pumping, can be used to polarize or analyze neutron beams because of the strong spin dependence of the neutron absorption cross section for ³He. ³He spin filters have been identified as important polarizing elements in the development of polarized neutron scattering instruments for the upcoming spallation neutron source (SNS) because they are broadband and suitable for divergent scattered beams. Here we report efficient polarization analysis of diffusely reflected neutrons in a reflectometry geometry using a hyperpolarized ³He spin filter in conjunction with a position-sensitive detector (PSD). We obtained spin-analyzed two-dimensional Qx-Qz reciprocal space maps for a patterned array of Co antidots in the saturated and the demagnetized states. We compared data obtained from a ³He analyzer and a PSD with those obtained from a conventional supermirror analyzer, and they are in good agreement. The preliminary results for the upcoming experiment with a ³He analyzer and a PSD using a patterned dot sample and/or a rare-earth alloy exchange spring will also be reported. For these experiments, ³He gas is polarized by the spin-exchange optical pumping (SEOP) method and stored in a uniform magnetic field provided by a shielded solenoid. We address two important issues for achieving the better performance of the ³He spin-analysis device: high ³He polarization and long relaxation time of the cell. Using a spectrally narrowed diode laser array we have recently achieved ³He polarizations of 74 % to 79 % in ³He cells ranging from 260 cm³ to 500 cm³ in volume.

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