Magnetism Reflectometer at SNS. Click image for a larger view.
The SNS Magnetism Reflectometer is designed mainly for reflectometry and high-angle diffraction studies of magnetic thin films, superlattices, and surfaces. The combination of the high-power SNS neutron source and the use of advanced neutron optics will also allow off-specular diffraction studies of in-plane structures. Today, even at the world's most advanced neutron sources, such experiments are extremely difficult to perform. The availability of polarized neutrons and polarization analysis suggests that the instrument will also be used for specific studies of non-magnetic thin film samples. Examples for the latter case include contrast variation, incoherent background reduction and phase determination for direct inversion of reflectivity data into real-space scattering-length density profiles.
Neutrons from the moderator are guided to the sample position at a distance of 18.5 m via a combination of a short channel beam bender and a tapered neutron guide. A horizontal scattering plane has been chosen to allow more convenient operation of the instrument and auxiliary equipment. Neutrons that are reflected/diffracted by the sample will be counted by a two-dimensional multidetector at a 20 m distance from the moderator. Polarizing neutron optical elements (polarizer, analyzer and spin flipper) determine the spin-state before and after scattering by the sample. The wavelength is determined by time-of-flight. The instrument is designed for 60 Hz operation. Bandwidth choppers restrict the total bandwidth of neutrons that are incident onto the sample to 3.5 Å when the instrument is collecting data in every time frame. The highest intensity will be available in the second frame (3.5 Å - 7.0 Å); however, by changing the phasing of the bandwidth choppers, the available 3.5 Å bandwidth can be shifted to either smaller or higher neutron wavelengths. Additionally, by changing the speed of the choppers, pseudo 30 Hz (or lower) operation can be realized with correspondingly wider wavelength bandwidth.
Magnetism Reflectometer at SNS. Click image for a larger view.
Besides the conventional use of a neutron reflectometer to analyze the structural and magnetic depth profiles of thin film structures, complementary kinetic studies (for example, probing the dynamic behavior of magnetic domains) are feasible. The capability of "time-tagging" pulses over a broad Q-range to study processes with longer time constants (msec to hours) is unique to the time-of-flight method and will be explored. Furthermore, studies of phonons and magnons at interfaces might be a real possibility with this instrument.
The SNS Instrument Oversight Committee (IOC) recommended in February 2000, the construction of two neutron reflectometry instruments to be used for (near) surface science experiments. One of these instruments will be dedicated to studies of liquid surfaces, and the other is designed for magnetism studies on thin films.
Recent publications about the instrument and its components:
"Decoupled moderators - Do we always need them? or: A new approach for pulse shaping"
Parizzi A., Lee W.T., Felcher G.P., Klose F., Journal of Neutron Research 11 (2003) 51 - 60
"Neutron polarization evolution calculations along the SNS Magnetism Reflectometer beam line"
A. A. Parizzi , F. Klose, V. Christoph, Physica B (submitted)
"Optimization of the SNS Magnetism Reflectometer neutron-guide optics using Monte Carlo Simulations"
F. Klose, W.T. Lee, Applied Physics A (Material Science & Processing) 74, Supplement 1, s1486 (2002)
"Modeling the neutron spin-flip process in a time-of-flight spin-resonance energy filter"
A.A. Parizzi, W.-T. Lee, F. Klose, Applied Physics A (Material Science & Processing) 74, Supplement 1, s1498 (2002)
"Possibilities for polarized pulsed neutron instrumentation based on the time-of-flight spin-resonance energy filter"
A.A. Parizzi, W.-T. Lee, F. Klose, Applied Physics A (Material Science & Processing) 74, Supplement 1, s1607 (2002)
"The SNS Magnetism Reflectometer: Basic Design and Neutron Guide Optimization Using Monte Carlo Simulations"
W.T. Lee and F. Klose, Authors; James L. Wood, Ian S. Anderson, Editors; Proceedings of SPIE Vol. 4509 (2001) 145 - 156
"Requirements for the optical elements of a spin-resonance energy filter for neutrons at reactor and pulsed source instruments"
A.A. Parizzi, W.T. Lee, F. Klose, Authors; James L. Wood, Ian S. Anderson, Editors; Proceedings of SPIE Vol. 4509 (2001) 114 - 125
"A Drabkin energy filter for experiments at a spallation neutron source"
A.A. Parizzi A., Felcher G.P., Klose F., ICANS-XV, 15th Meeting of the International Collaboration on Advanced Neutron Sources, Proceedings, Tsukuba/Japan, November 6-9, 2000, p. 572 - 580
