Neutron polarizers based on polarized 3He

The goal of this work, which is a collaborative effort between Indiana University, NIST, and Hamilton College, is to extend the technique of polarized neutron scattering into new domains by the development and application of polarized 3He-based neutron spin filters. After the IPNS experiment which measured Zeeman sp[litting in surface scattered neutrons using a polarized 3He cell as a polarization analyzer transporterd by car from Bloomington to Chicago, the Indiana work focused on technical developments to improve the 3He polarization of the Indiana compression system. The compression system was rebuilt with a new valve system which allows gas trapped in the dead volume of the compressors at the end of the piston stroke to be exhausted and conducted back to the optical pumping cell where it can be repolarized. We also incorporated a new intermediate storage volume made at NIST from 1720 glass which will reduce polarization losses between the compressors. Furthermore, we improved the stability of the 1083 nm laser by cooling the LMA rod. We achieved 60% 3he polarization in the optical pumping cell and 87% preservation of the polarization during compression. In parallel we built a magnetically-shielded transport solenoid for use on neutron scattering instruments such asmore » POSY which achieves a fractional field uniformity of better than 10-3 per cm. The field was mapped using an automated 3D field mapping system for in-situ measurement of magnetic field gradients Diluted magnetic semiconductors offer many exciting opportunities for investigation of spintronic effects in solids and are certain to be one of the most active areas of condensed matter physics over then next several years. These materials can act as efficient spin injectors for devices that make use of spin-dependent transport phenomena. We just (late July 2002) finished a neutron reflectivity experiment at NIST on a GaMnAs trilayer film. This material is a ferromagnetic semiconductor which is of interest for possible applications in spintronics. With the temperature at 12 K and H=235G which saturated both layers' moment to be parallel to the guide field we saw ferromagnetic alignment (FM) of the two outer layers. We also have evidence that the two magnetic layers have different Tc's, and can therefore be used to fabricate a spin-valve. We see a peak at a location in q-space that could correspond to an anti-ferromagnetic state. Finally, we made progress in assembling a spin-exchange optical pumping system which will eventually be relocated to IPNS as an on-site neutron spin filter. As this is written we are preparing for the first effort to optically pump 3He using spin exchange at Indiana. This device will be operational before the end of the present grant. The goal of the work funded by the subcontract to Hamilton College was to support the work of NIST and Indiana in developing 3He-based neutron spin filters for use in polarized neutron scattering applications. Most of the grant period was used by Hamilton to construct the required infrastructure, including 3He cell filling and NMR systems. The main achievement at Hamiltonin is the successful operation of the spin exchange filling system to make a 3He spin exchange cell with a spin relaxation time of 300 hours. This very long relaxation time bodes well for the further development of spin exchange 3He spin filters. Hamilton also constructed a portable NMR device that was used at Indiana to conduct the compression system measurements.« less