Journal of large-scale research facilities, 3, A104 (2017) http://dx.doi.org/10.17815/jlsrf-3-107-1 Published: 26.01.2017 E4: The 2-Axis Di�ractometer at BER II Helmholtz-Zentrum Berlin für Materialien und Energie * Instrument Scientists: - Dr. Karel Prokes, Helmholtz-Zentrum Berlin für Materialien und Energie phone: +49 30 8062-42804, email: prokes@helmholtz-berlin.de - Dr. Fabiano Yokoachiya, Helmholtz-Zentrum Berlin für Materialien und Energie phone: +49 30 8062-42804, email: fabiano.yokoachiya@helmholtz-berlin.de Abstract: The double-axis di�ractometer E4 is operated by the Helmholtz-Zentrum Berlin. It is suited for magnetic structure determinations and parametric studies on single crystals in a wide range of ex- ternal conditions. Pyrolytic graphite and germanium focusing monochromators o�er two �xed neutron incident wavelengths of about 1.0*106 ncm−2s−1. 1 Introduction The instrument is primarily suited for magnetic structure determination under various conditions, which includes magnetic �elds up to 17 T, temperatures down to 30 mK and hydrostatic pressures up to 10 kbar. The application of uniaxial pressure and use of auxiliary methods (e.g. electrical resistivity, ac susceptibility, pyroelectric current measurements) is also possible. The most common application is to reveal spatial arrangement ordered spin structures to study magnetic and/or crystal structure phase transitions and construction of phase diagrams. Using the polarized neutrons option facilitates the sep- aration of magnetic contributions from nuclear scattering. The measurement of �ipping ratios allows registration of very weak magnetic scattering. The monochromator shielding contains one beam channel at 2ΘM = 42.5°. This position corresponds to the incident wavelength of 0.24 nm for the vertical focusing PG(002) monochromator and 0.122 nm for the double-focusing Ge(311) monochromator. Both monochromators are operated remotely. Saphire and PG �lters o�er an e�ective suppression of unwanted epithermal and λ /2 (for PG monochromator) neutrons. Before the monochromator position a radial collimator is placed. *Cite article as: Helmholtz-Zentrum Berlin für Materialien und Energie. (2017). E4: The 2-Axis Di�ractometer at BER II. Journal of large-scale research facilities, 3, A104. http://dx.doi.org/10.17815/jlsrf-3-107-1 1 http://jlsrf.org/ http://dx.doi.org/10.17815/jlsrf-3-107-1 http://dx.doi.org/10.17815/jlsrf-3-107-1 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 3, A104 (2017) http://dx.doi.org/10.17815/jlsrf-3-107-1 The secondary �ight path is conical and primarily without collimators that can be placed (with �at monochromator) optionally. Motorized slits o�er a possibility to reduce the background. The addi- tional option of polarized neutrons uses a super mirror bender and a π−�ipper. The instrument runs under the system CARESS; automatic control of temperature and magnetic �eld is provided. An Eule- rian cradle can optionally be used to access the four dimensional Q-ω -space. The instrument is equipped with a position sensitive 200x200 mm2 detector before which an oscillating collimator is placed. The detector is mounted assymetrically so that it covers below the scattering plane about 4 degrees and above about 10 degrees. The coverage in 2θ amounts to about 14 degrees. Figure 1: View of E4 with an extensive sample environment installed: the vertical cryomagnet and the dilution refrigerator. 2 Typical applications Typical applications include: • Magnetic structure determination • Study of magnetic and structural phase transitions • Determination of magnetic phase diagrams • Study of critical points as a function of magnetic �eld and temperature • Measurement of correlation functions above the ordering temperature 2 http://dx.doi.org/10.17815/jlsrf-3-107-1 https://creativecommons.org/licenses/by/4.0/ http://dx.doi.org/10.17815/jlsrf-3-107-1 Journal of large-scale research facilities, 3, A104 (2017) 3 Instrument layout Figure 2: Schematic view of E4. 3 http://dx.doi.org/10.17815/jlsrf-3-107-1 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 3, A104 (2017) http://dx.doi.org/10.17815/jlsrf-3-107-1 4 Technical Data Beam tube R 2 Collimation automatic change of α 1 = 40’ radial, open geometrical divergence: 60’ manual variation of α 2 (optional 10’, 20’, 40’) α 3 (oscillating radial) Monochromator PG (002) with variable vertical curvature Ge (113) double focusing Take o� angle of monochromator 2ΘM = 42.5° Wave length λ =0.244 nm (PG) or 0.122 nm (Ge) Flux 0.95·106 n/cm2s (PG) 0.9·106 n/cm2s (Ge) 0.3·106 n/cm2s polarized (PG+bender) Range of scattering angles 0° ≤ 2Θ ≤ 120° (with con�gurational restrictions related to sample environment) Angle resolution Depends on setting Sample size From 1 mm3 for topic-focused studies Detector 2D detector 200x200 mm2 (removable oscillating radial collimator in front), variable distance (700-950 mm) Polarized neutrons Yes (super mirror bender) Please contact the instrument scientist to discuss in advance Instrument options Polarization analysis (super mirror analysis) Sample environment • Horizontal magnetic �eld < 6 T • Vertical magnetic �eld < 17 T • Temperature range 0.03 - 600 K • Hydrostatic pressure 0 - 10 kbar • 4-circle mode Software CARESS, BEAN, set of supporting programs to deal with 2D data Table 1: Technical parameters of E4. 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