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Polarized Neutron Reflectometry of a Patterned Magnetic Film with a 3He analyzer and a Position Sensitive Detector

Wangchun Chen and Thomas R. Gentile

Division 846, Physics Laboratory

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

NIST Center for Neutron Research, MSEL

S. Adenwalla

University of Nebraska

Polarized Neutron scattering techniques are very important and powerful probes for the fundamental structures of magnetic materials. Polarized 3He gas, produced by optical pumping, can be used to polarize or analyze neutron beams because of the large spin dependence of the neutron absorption cross section for 3He. Polarized 3He based neutron spin filters are expected to play a key role in the polarized neutron scattering instruments because of their unique ability to polarize broadband neutron beams and analyze divergent scattered beams.
 
 

The work presented describes our successful development of polarized neutron reflectometry (PNR) using a polarized 3He analyzer in conjunction with a position sensitive detector (PSD). PNR is capable of providing information on the depth profile of the magnetization, in-plane domains and interfacial roughness of magnetic thin films. This work was carried out on the NG1 polarized neutron reflectometer at the NCNR (NIST Center for Neutron Research). We measured the specular and diffuse reflectivity of a patterned array of magnetic Co antidots. Analysis of the data yielded spin-analyzed two-dimensional Qx-Qz reciprocal space maps for the sample in magnetized and demagnetized states. We compared the measurements obtained with a 3He analyzer and a PSD with those obtained using a conventional supermirror analyzer and a pencil 3He detector. The results are in good agreement. The combination of a polarized 3He analyzer and a PSD allows for polarization analysis for a broad range of scattering angles, which substantially increases the efficiency of studies of diffuse magnetic scattering. For this experiment, 3He gas was polarized by the spin-exchange optical pumping (SEOP) method and stored in a uniform magnetic field provided by a shielded solenoid. The performance of the 3He analyzer has been improved following our recent success in fabricating cells with relaxation times of several hundred hours and producing 3He gas with approximately 70 % to 75 % polarization using a spectrally narrowed diode laser array.

Wangchun Chen

NIST

100 Bureau Drive, MS 8461

Gaithersburg, MD 20899-8461

Phone: 301-975-6222

Email: wcchen@nist.gov