Polarized Beam OperationA polarized beam option has been developed for BT-7, utilizing 3He polarizers immediately before and after the sample. This gives BT-7 full polarized beam capability for experiments where a guide field (only) is applied at the sample position to control the direction of polarization, and thereby the cross sections. The system is fully operational. The 3He itself can be inverted to achieve the alternate spin state before or after the sample. An adjustable guide field at the sample position is under computer control to manipulate the polarization direction perpendicular or parallel to the scattering plane, or in an angular range in the scattering plane. Spin Flippers are no longer used.
A vertical-field polarized beam option with the 7 T magnet, at relatively modest fields of 2 T and below, is also availble for BT-7.
Please note that optically pumping the cells takes ~1 day to get good 3He polarization, and other instruments use the polarizers as well. Hence the use of the polarized beam option must be requested and scheduled well in advance of an experiment.
Sample Mounting for Polarized Beam Operation.
There are special requirements that must be taken into account when mounting samples for polarized beam measurements. In particular, no stainless steel of any kind should be used in or on the sample container, as that can cause uncontrolled depolarization of the neutrons. In addition, non-magnetic screws such as aluminum or brass screws should be used to mount the sample onto the copper block, for example in a closed cycle refrigerator.
For operation below 1.5 K, in a dilution or 3He3refrigerator, additional care should be used to avoid superconducting materials. Cd inside the sample container has caused problems (TC = 0.52 K, HC = 2.8 mT). Pure aluminum has TC = 1.2 K, HC = 10 mT; 6061 Al alloy used for sample mounts and containers has a lower or no transition, depending on the detailed compoisiton and fabrication history, and can also cause problems in some circumstances.
In addition to the BT-7 instrument publication
Double Focusing Thermal Triple Axis Spectrometer at the NCNR
,J. W. Lynn, Y. Chen, S. Chang, Y. Zhao, S. Chi, W. Ratcliff, II, B. G. Ueland, and R. W. Erwin, Journal of Research of NIST 117, 61-79 (2012),
please use the following publication to acknowledge polarized beam work on BT-7:
3He Neutron Spin Filters for a Thermal Neutron Triple Axis Spectrometer, W. C. Chen, G. Armstrong, Y. Chen, B. Collett, R. Erwin, T. R. Gentile, G. L. Jones, J. W. Lynn, S. McKenney and J. E. Steinberg, Physica B 397, 168 (2007).
Publications that have utilized the polarized beam capability on BT-7
Magnetic Order of the Iron Spins in NdOFeAs, Y. Chen, J. W. Lynn, G. F. Chen, G. Li, Z. C. Li, J. L. Luo, N. L. Wang, P. Dai, C. dela Cruz, and H. A. Mook Phys. Rev. B78, 064515 (2008).
Single Ferroelectric and chiral magnetic domain of single-crystalline BiFeO3 in an electric field, Seongsu Lee, Taekjib Choi, W. Ratcliff II, R. Erwin, S-W. Cheong, and V. Kiryukhin, Phys. Rev. B 78, 100101(R) (2008).
Spin Waves in the Magnetoelectric Effect LiCoPO4 Compound, W. Tian, J. Li, J. W. Lynn, J. L. Zarestky, and D. Vaknin, Phys. Rev. B 78, 184409 (2008)
End-compensated magnetostatic cavity for polarized 3He neutron spin filter, J.W. McIver, R. Erwin, W.C. Chen, and T.R. Gentile, Rev. Sci. Instrum. 80, 063905 (2009).
Applications of 3He neutron spin filters at the NCNR, W. C. Chen, R. Erwin, J. W. McIver III, S.Watson, C.B. Fu, T. R. Gentile, J. A. Borchers, J. W. Lynn, and G. L. Jones, Physica 404B, 2663 (2009).
Coupled Magnetic and Ferroelectric Hysteresis in Multiferroic Ni3V2O8, I. Cabrera, M. Kenzelmann, G. Lawes, Y. Chen, W. C. Chen, R. Erwin, T. R. Gentile, J. B. Leao, J. W. Lynn, N. Rogado, R. J. Cava, and C. Broholm, Phys. Rev. Lett. 103, 087201 (2009).
Nitrogen Contamination in Elastic Neutron Scattering, Songxue Chi, Jeffrey W. Lynn, Ying Chen, William Ratcliff II, Benjamin G. Ueland, Nicholas P. Butch, Shanta R. Saha, Kevin Kirshenbaum, and Johnpierre Paglione, Meas. Sci. Technol. 22, 047001 (2011).
Antiferromagnetic order and superlattice structure in the nonsuperconducting and superconducting RbyFe1.6+xSe2, Meng Wang, Miaoyin Wang, G. N. Li, Q. Huang, C. H. Li, G. T. Tan, C. L. Zhang, H. B. Cao, Wei Tian, Yang Zhao, Y. C. Chen, X. Y. Lu, Bin Sheng, H. Q. Luo, S. L. Li,1 M. H. Fang, J. L. Zarestky, W. Ratcliff, M. D. Lumsden, J. W. Lynn, and Pengcheng Dai, Phys. Rev. B 84, 094504 (2011).
Studies of long range order and excitations in the iron arsenide superconductors, Pratt, Daniel Keith, (2011). Graduate Theses and Dissertations. http://lib.dr.iastate.edu/etd/10177
Double Focusing Thermal Triple Axis Spectrometer at the NCNR
,J. W. Lynn, Y. Chen, S. Chang, Y. Zhao, S. Chi, W. Ratcliff, II, B. G. Ueland, and R. W. Erwin, Journal of Research of NIST 117, 61-79 (2012).
Carrier Localization and Electronic Phase Separation in a doped Spin-Orbit Driven Mott Phase in Sr3(Ir1-xRux)2O7, Chetan Dhital, Tom Hogan, Wenwen Zhou, Xiang Chen, Zhensong Ren, Mani Pokharel, Yoshinori Okada, M. Heine, Wei Tian, Z. Yamani, C. Opeil, J. S. Helton, J. W. Lynn, Ziqiang Wang, Vidya Madhavan, and Stephen D. Wilson, Nature Communications
.5, 3377 (2014).
Spurious Peaks Arising from Multiple Scattering Events the Sample Environment in Inelastic Neutron Scattering, Lothar Pintschovius, Dmitry Reznik, Frank Weber, Philippe Bourges, Dan Parshall, Ranjal Mittal, Samrath LaI Chaplot, Rolf Heid, Thomas Wolf, Daniel Lamago, and Jeffrey W. Lynn, J. Appl. Cryst. 47, 1472 (2014).
Quadrupole Order in the Frustrated Pyrochlore Tb2+xTi2−xO7+y, H. Takatsu, S. Onoda, S. Kittaka, A. Kasahara, Y. Kono, T. Sakakibara, Y. Kato, B. Fåk, J. Ollivier, J. W. Lynn, T. Taniguchi, M. Wakita, and H. Kadowaki, Phys. Rev. Lett. 116, 217201 (2016).
Complex magnetic incommensurability and electronic charge transfer through the ferroelectric transition in multiferroic Co3TeO6, Chi-Hung Lee, Chin-Wei Wang, Yang Zhao, Wen-Hsien Li, Jeffrey W. Lynn, A. Brooks Harris, Kirrily Rule, Hung-Duen Yang, and Helmuth Berger, (submitted).
Last modified 11-October-2016 by website owner: NCNR (attn: Jeff Lynn)