Neutron Diffuse Reflectometry of Magnetic Thin Films with a 3He Analyzer

Polarized neutron reflectometry (PNR) is a powerful probe that characterizes the magnetization depth profile and magnetic domains in magnetic thin films. Although the conventionally used supermirrors are well-matched for specular PNR, they have limited angular acceptance and hence are impractical for complete characterization of the magnetic off-specular scattering where polarization analysis for diffusely reflected neutrons is required. Polarized $^{3}$He 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 $^{3}$He. Here we report efficient polarization analysis of diffusely reflected neutrons in a reflectometry geometry using a polarized $^{3}$He analyzer in conjunction with a position-sensitive detector (PSD). We obtained spin-resolved two-dimensional Q$_{x}$-Q$_{z}$ reciprocal space maps for a patterned array of Co antidots in both the saturated and the demagnetized states. The preliminary results for a patterned amorphous bilayer, Gd$_{40}$Fe$_{60}$/ Tb$_{55}$Fe$_{45}$, measured with a $^{3}$He analyzer and a PSD will also be discussed. Using the spin exchange optical pumping method we have achieved record high $^{3}$He polarizations of 76{\%} on the neutron beam line where we measured an initial analyzing efficiency of 0.97 and a neutron transmission for the desired spin state of 0.45.