crystals
Article DEMAND, a Dimensional Extreme Magnetic Neutron Diffractometer at the High Flux Isotope Reactor
Huibo Cao 1,* , Bryan C. Chakoumakos 1 , Katie M. Andrews 1, Yan Wu 1, Richard A. Riedel 2, Jason Hodges 2, Wenduo Zhou 1, Ray Gregory 2, Bianca Haberl 1, Jamie Molaison 1 and Gary W. Lynn 1
1 Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA; [email protected] (B.C.C.); [email protected] (K.M.A.); [email protected] (Y.W.); [email protected] (W.Z.); [email protected] (B.H.); [email protected] (J.M.); [email protected] (G.W.L.) 2 Neutron Technologies Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA; [email protected] (R.A.R.); [email protected] (J.H.); [email protected] (R.G.) * Correspondence: [email protected]; Tel.: +1-865-574-3011
Received: 8 December 2018; Accepted: 19 December 2018; Published: 21 December 2018
Abstract: A two-dimensional (2D) Anger camera detector has been used at the HB-3A four-circle single-crystal neutron diffractometer at the High Flux Isotope Reactor (HFIR) since 2013. The 2D detector has enabled the capabilities of measuring sub-mm crystals and spin density maps, enhanced the efficiency of data collection and phase transition detection, and improved the signal-to-noise ratio. Recently, the HB-3A four-circle diffractometer has been undergoing a detector upgrade towards a much larger area, magnetic-field-insensitive, Anger camera detector. The instrument will become capable of doing single-crystal neutron diffraction under ultra-low temperatures (50 mK), magnetic fields (up to 8 T), electric fields (up to 11 kV/mm), and hydrostatic high pressures (up to 45 GPa). Furthermore, half-polarized neutron diffraction is also available to measure weak ferromagnetism and local site magnetic susceptibilities. With the new high-resolution 2D detector, the four-circle diffractometer has become more powerful for studying magnetic materials under extreme sample environment conditions; hence, it has been given a new name: DEMAND.
Keywords: single-crystal neutron diffraction; polarized neutron diffraction; position sensitive detector; magnetism; magnetic materials; atomic magnetic susceptibility; local magnetic susceptibility; ultra-low temperature; high pressure; Anger camera
1. Introduction Single-crystal neutron diffraction is known for characterizing magnetic and nuclear structures. However, it is limited by the availability of intense neutron resources and large crystals. New detector technologies have made high-resolution and high-efficiency large area detectors possible, which can speed up the data collection and enable the capability of measuring more detailed information beyond a structure solution, such as short-range order, strain, and defect studies, by modeling the peak profile. A recently developed two-dimensional (2D) magnetic-field-insensitive detector has been equipped at the HB-3A four-circle diffractometer housed at the High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory (ORNL). The detector uses solid-state silicon photomultipliers (SiPM) [1]. Fast data collection by snapshotting the Bragg peaks and short-range order studies have been introduced. The new Anger camera detector on HB-3A enables the full capability of single-crystal unpolarized/polarized neutron diffraction under a much more diverse set of sample environment equipment, including ultra-low-temperature cryostats (50 mK), high-field cryomagnets (up to 8 T), and high-pressure cells (up to 45 GPa), and extends the capability of single-crystal neutron
Crystals 2019, 9, 5; doi:10.3390/cryst9010005 www.mdpi.com/journal/crystals Crystals 2019, 9, 5 2 of 9 diffraction for studying unconventional magnetic materials, including low-dimensional magnets, highly frustrated magnets, 4d-5d strong spin–orbital coupled magnets, and molecular magnets. By extending these capabilities, the traditional HB-3A four-circle diffractometer [2] has become an extreme sample environment magnetic single-crystal neutron diffractometer with a high-resolution 2D detector (DEMAND). After fully completing the detector upgrade, DEMAND will be able to expand its capacity for neutron diffraction and support a more advanced single-crystal neutron diffraction community together with other similar types of instruments, including the 6T2 thermal neutron four-circle diffractometer (FCD) at LLB, France [3], the D9 hot neutron FCD [4] and the D10 FCD with three-axis energy analysis [5] at ILL, France, HEiDi [6] and POLI [7] at FRM-II, Germany, the ZEBRA thermal single-crystal diffractometer [8] at PSI, Switzerland, and the SENJU extreme environment single-crystal neutron diffractometer [9] at J-PARC, Japan. This paper is the continuation of the earlier one reported in 2011 [2], and so will focus on the newly available area detector, the new sample environment equipment, polarized neutron diffraction, and related new science areas.
Crystals 2018, 8, x FOR PEER REVIEW 2 of 9 2. Anger Camera Detector Theof sample HB-3A environment four-circle diffractometerequipment, including had run ultra with‐low a‐3temperatureHe point detector cryostats since (50 2010mK), andhigh started‐field to use acryomagnets 2D Anger camera (up to 8 inT), 2013. and high The‐pressure detector cells is a (up scintillator-based to 45 GPa), and extends 2D Anger the capability camera with of single a size‐ of crystal neutron diffraction for studying unconventional magnetic materials, including low‐ 51 mm × 51 mm, in actuality a prototype detector for the instrument TOPAZ at the Spallation Neutron dimensional magnets, highly frustrated magnets, 4d‐5d strong spin–orbital coupled magnets, and Source (SNS) at ORNL [10]; we call this Camera-I. The new detector is magnetic-field insensitive due molecular magnets. By extending these capabilities, the traditional HB‐3A four‐circle diffractometer to the[2] use has of become solid an SiPM, extreme and sample it also environment has a better magnetic pixel resolution single‐crystal (0.65 neutron mm) thandiffractometer Camera-I with (1 mm pixela resolution). high‐resolution We 2D call detector the new (DEMAND). SiPM model After Camera-II, fully completing and its the prototype detector upgrade, with a 2DEMAND× 2 array of sensorwill modules be able to (Figure expand1a) its has capacity already for been neutron commissioned diffraction and and support successfully a more runadvanced for a full single reactor‐crystal cycle. Therefore,neutron a larger diffraction 2D Anger community camera together detector with of theother Camera-II similar types version of instruments, will be installed including at HB-3A the 6T2 at the beginningthermal of neutron 2019. Its four size‐circle of 348 diffractometer (vertical) mm (FCD)× 116 at (horizontal) LLB, France mm[3], the can D9 cover hot neutron vertical FCD angles [4] ofand 50 ◦ at a 30-cmthe distanceD10 FCD to with the three sample‐axis position, energy analysis allowing [5] the at instrumentILL, France, to HEiDi run in [6] a and two-axis POLI mode[7] at FRM with‐ accessII, to a largeGermany, reciprocal the ZEBRA space thermal volume, single which‐crystal allows diffractometer for effective [8] single-crystal at PSI, Switzerland, neutron and diffraction the SENJU using extremeextreme sample environment environments. single‐crystal Soon, theneutron detector diffractometer will be expanded [9] at J‐PARC, to the Japan. size of This 348 paper× 348 is mm the 2 as continuation of the earlier one reported in 2011 [2], and so will focus on the newly available area shown in Figure1b. Except for the better pixel resolution, larger size, and tolerance to magnetic fields, detector, the new sample environment equipment, polarized neutron diffraction, and related new the new detector is similar to the current prototype Anger camera using conventional photomultiplier science areas. tubes (PMTs) [10]. Here, we will introduce some new capabilities gained from the Anger camera 3 detector2. Anger compared Camera to Detector the He point detector.
(a) (b)
Figure 1. (a) A view of the solid-state silicon photomultiplier (SiPM) made of a 2 × 2 array of sensor Figure 1. (a) A view of the solid‐state silicon photomultiplier (SiPM) made of a 2 × 2 array of sensor modules (116 mm × 116 mm). (b) DEMAND: the future view of the HB-3A single-crystal neutron modules (116 mm × 116 mm). (b) DEMAND: the future view of the HB‐3A single‐crystal neutron diffractometer after installing the 3 × 3 SiPM Anger camera detector. The χ/φ circles shown are diffractometer after installing the 3 × 3 SiPM Anger camera detector. The χ/ϕ circles shown are interchangeable with an ultra-low temperature cryostat or a cryomagnet, so the diffractometer can be interchangeable with an ultra‐low temperature cryostat or a cryomagnet, so the diffractometer can be run inrun either in either four-circle four‐circle mode mode or or two-axis two‐axis mode, mode, respectively. respectively.
The HB‐3A four‐circle diffractometer had run with a 3He point detector since 2010 and started to use a 2D Anger camera in 2013. The detector is a scintillator‐based 2D Anger camera with a size of 51 mm × 51 mm, in actuality a prototype detector for the instrument TOPAZ at the Spallation Neutron Source (SNS) at ORNL [10]; we call this Camera‐I. The new detector is magnetic‐field insensitive due to the use of solid SiPM, and it also has a better pixel resolution (0.65 mm) than Camera‐I (1 mm pixel resolution). We call the new SiPM model Camera‐II, and its prototype with a 2 × 2 array of sensor modules (Figure 1a) has already been commissioned and successfully run for a full reactor cycle. Therefore, a larger 2D Anger camera detector of the Camera‐II version will be installed at HB‐3A at the beginning of 2019. Its size of 348 (vertical) mm × 116 (horizontal) mm can cover vertical angles of 50° at a 30‐cm distance to the sample position, allowing the instrument to run in a two‐axis mode with access to a large reciprocal space volume, which allows for effective single‐crystal neutron diffraction using extreme sample environments. Soon, the detector will be expanded to the size of 348 × 348 mm2 as shown in Figure 1b. Except for the better pixel resolution, larger size, and tolerance
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2.1. 3He Detector and 2D Anger Camera Detector The 3He detector had seven anodes, each with a size of 10 mm in diameter, and only the central anode was used [2]. Camera-I has a size of 51 × 51 mm2. We measured the same crystal, a natural 3 tetrahedrite Cu12Sb4S13, at room temperature in the same mounting orientation with both the He detector and the 2D Anger camera detector. The crystal has a spherical shape, and is 3.7 mm in diameter. The neutron wavelength of 1.008 Å from the bent Si-331 [2] was used for the data collection. Figure2 shows the peak (2 2 2) measured by both detectors. The peak image was observed in Camera-I (Figure2a). The rocking-curve scans with both detectors are plotted together in Figure2b. The detector signal is from the predefined region-of-interest (ROI), which has a size of 25 mm in diameter. Camera-I observed 60% extra neutron counts, while the background is about the same at 2 counts/s/cm2 for both detectors. The conversion efficiency of the 3He detector is ~99% for thermal neutrons of 1.008 Å, while the conversion efficiency of Camera-I is estimated to be 80%. The extra intensity gain is due to the Bragg peak size being larger than the aperture of the central anode. Table1 lists the structural and refinement parameters of Cu 12Sb4S13 from the data collected with both detectors for comparison, and Figure3 shows the plots of the observed structure factors: 2 2 squared, F obs, versus the calculated F cal. The results are consistent with each other within the error bars. By optimizing the ROI, the rocking-curve scans can have a lower background per scanning point, which benefits measurements of small crystals. The ROI can be predefined in the data acquisition program SPICE [11] before starting the data collection or can be redefined in MantidPlot [12] after the experiment. For Camera-I, the rocking-curve scan covers the full peak profile of each Bragg reflection, and the data can be sliced in reciprocal space, which can be used to calibrate dimensionalities of ordering parameters and track structural transitions. The larger the detector gets, the faster new phase searches can run. New phases are usually indicated by peak broadening/splitting, superlattice peaks, magnetic satellite peaks, or/and diffuse scattering. The high pixel resolution ensures that the high instrument resolution is not sacrificed (the closest detector-to-sample distance is ~30 cm for Camera-I without losing the instrument resolution, and it is ~20 cm for Camera-II). The complete DEMAND (with the full 3 × 3 array of detector modules) will advance the data collection speed and the data completeness, enable the access to extreme sample environment conditions that only allow limited or no tilting of sample (Section3: sample environment), and expand the reciprocal space coverage for half-polarized neutron diffraction to reconstruct magnetization density maps and study atomic magnetic susceptibilities (Section4: polarized neutron diffraction) under various sample environment conditions. CrystalsCrystals 20182019,, 89,, x 5 FOR PEER REVIEW 44 of of 9 9 Crystals 2018, 8, x FOR PEER REVIEW 4 of 9
(a) (b) (a) (b) Figure 2. (a) A snapshot of the Bragg peak (2 2 2) of a sphere of a natural tetrahedrite Cu12Sb4S13 crystal Figure 2. (a) A snapshot of the Bragg peak (2 2 2) of a sphere of a natural tetrahedrite Cu12Sb43S13 crystal recordedFigure 2. by(a )the A Camera snapshot‐I ofdetector. the Bragg (b) θ‐ peak2θ scans (2 2 2) of ofthe a Bragg sphere peak of a (2 natural 2 2) recorded tetrahedrite by the Cu He12Sb point4S13 3 detectorcrystalrecorded recorded and by thethe byCameraCamera the Camera-I‐‐II detector. detector. (b) θ‐2 (θ b)scansθ-2θ scansof the of Bragg the Bragg peak (2 peak 2 2) (2 recorded 2 2) recorded by the by He the point3He pointdetector detector and the and Camera the Camera-I‐I detector. detector.
(a) (b) (a) (b) FigureFigure 3. ((aa)) Observed Observed versus versus calculated calculated structure structure factors factors squared. The The data data were were collected collected by by Figure 3. (a) Observed versus calculated structure3 factors squared. The data were collected by rockingrocking-curve‐curve scans scans through through each each reflection reflection with with the the He3He point point detector detector (black (black solid solid squares) squares) and andthe rocking‐curve scans through each reflection with the 3He point detector (black solid squares) and the Camerathe Camera-I‐I detector detector (red (red open open circles). circles). The The blue blue open open diamonds diamonds represent represent the the data data collected collected by by Camera‐I detector (red open circles). The blue open diamonds represent the data collected by snapshotting each Bragg peak with the Camera‐I detector (the F22calc were calculated from the same snapshotting each Bragg peak with the Camera-I detector (the F calc were calculated from the same snapshotting each Bragg peak with the Camera‐I detector (the F2calc were calculated from the same structurestructure parametersparameters that that were were refined refined from from the datathe collecteddata collected by rocking-curve by rocking scans‐curve with scans the Camera-Iwith the structure parameters that were refined from the data collected by rocking‐curve scans with the Cameradetector).‐I detector). (b) The full-widths-at-half-maximum (b) The full‐widths‐at‐half‐ (FWHMs)maximum of (FWHMs) the rocking-curve-scanned of the rocking‐curve peaks‐scanned versus Camera‐I detector). (b) The full‐widths‐at‐half‐maximum (FWHMs) of the rocking‐curve‐scanned peaksthe detector versus anglethe detector 2θ. The angle widths 2θ. The were widths obtained were by obtained fitting eachby fitting peak each with peak a Gaussian with a Gaussian function. peaks versus the detector angle 2θ. The widths were obtained by fitting each peak with a Gaussian function.The larger The the larger error-bar, the error the weaker‐bar, the is weaker the corresponding is the corresponding peak. The peak. peaks The with peaks FWHM with error-bars FWHM error larger‐ function. The larger the error‐bar, the weaker is the corresponding peak. The peaks with FWHM error‐ barsthan larger 0.4◦ are than not 0.4° realistic are not although realistic they although are still they plotted. are still plotted. bars larger than 0.4° are not realistic although they are still plotted. 2.2.2.2. Capability Capability for for Tiny Tiny Crystals 2.2. Capability for Tiny Crystals TheThe Anger Anger camera camera detector detector enables enables the the capability capability for for rapid rapid data data collection collection by by snapshotting snapshotting Bragg Bragg peakspeaksThe instead instead Anger of of camerascanning scanning detector through through enables each each thereflection reflection capability (typically (typically for rapid 21 21 datapoints points collection at at the the minimum minimum by snapshotting are are used used Bragg for for stepsteppeaks scans). scans). instead The The of strong strong scanning reflections, reflections, through e.g., each over reflection 1000 counts/s, (typically can can 21 be bepoints measured measured at the by byminimum rocking rocking-curve‐ curveare used scans scans for atatstep 1 second/point, scans). The strong and and the thereflections, mosaic mosaic information informatione.g., over 1000 can can counts/s, be be extracted extracted can befrom from measured those those strong strong by rocking peaks. peaks.‐curve The The weak weakscans peakspeaksat 1 second/point, that requirerequire a aand long long the counting counting mosaic time informationtime can can be measuredbe canmeasured be extracted by snapshottingby snapshotting from those the peak thestrong peak signal peaks. signal at each The at Bragg weakeach Braggpositionpeaks position that and require corrected and corrected a long by the counting by mosaic the mosaic distributiontime can distribution be andmeasured instrument and instrumentby snapshotting resolution. resolution. The the data peak The collected datasignal collected at on each the Bragg position and corrected by the mosaic distribution and instrument resolution. The data collected
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same tetrahedrite Cu12Sb4S13 were plotted in blue open squares in Figure3a, and the corresponding 2 F cal were calculated from the structure parameters listed in Table1 (the Camera-I detector) except for the scale factor. The discrepancies are because the peak widths are not only Q (or 2θ)-dependent as shown in Figure3b. The figure plots the peak width versus the detector angle 2 θ, which includes the sample mosaic and instrument resolution information. Although, in principle, we should be able to measure a structure by snapshotting the Bragg peaks, the formula of the peak width must be given or modeled. Currently, it only works for tiny high-quality crystals, which is mostly important with this kind of data collection considering that it is not possible to collect a full data set within a reasonable amount of beam time by rocking-curve scanning each reflection. The data collection of 463 reflections with rocking-curve scans takes ~1 min per reflection and 7.7 h in total (including motor motion and data communication time) with 21 points/scan at 1 s/point. Snapshotting 463 reflections with 10 s/point takes 20 s per reflection and 2.6 h in total, including motor motion and data communication time. Snapshotting Bragg peaks is especially important for measuring weak signals or tiny crystals. For tiny crystals with perfect quality (the mosaic is instrument-resolution-limited), all of the reflections can be snapshotted and corrected by the instrument resolution. The smallest crystal that has been 3 measured at HB-3A is an YbFeO3 hexagonal ferrite thin film (5 mm × 5 mm × 50 nm~0.001 mm ), and the ordered Fe-moment size determined was 2 µB [13]. The weak superlattice peaks originating from an Fe/Cu site order in a superconductor material NaCuFeAs were also collected by snapshotting Bragg peaks at HB-3A, and the refinement confirmed that it is a Fe/Cu stripe structure. The counting time for each snapshot was 10 min, and details for that study are reported in [14].
Table 1. The structural parameters of Cu12Sb4S13 measured at room temperature at DEMAND using the Camera-I and 3He point detectors. The space group is I-43m and the lattice parameter a = 10.342(8) 1 1 Å. The atomic positions are Cu1: Cu ( 2 , 0, 4 ); Cu2: Cu (0, 0, z); Sb1: Sb (x, x, x); S1: S (x, x, z); S2: S (0, 0, 0). The atomic displacement parameters U have units of Å2 and only non-zero U elements are listed.
Parameter 2D Anger Camera (Camera-I) 3He Point Detector Scale 2.88(5) 1.81(4) Extinction 0.19(4) 0.21(8) 2 RF 4.02 4.59 2 RF w 4.89 10.8 RF 3.49 5.02 χ2 0.309 1.99 No. of reflections 463 323 Cu2: z 0.2169(3) 0.2163(3) Sb1: x 0.2652(2) 0.26511(1) S1: x 0.8824(4) 0.8828(2) S1: z 0.3598(4) 0.3593(2) Cu1: U11 = U22 0.0189(8) 0.0201(7) Cu1: U33 0.023(1) 0.026(1) Cu2: U11 = U22 0.072(1) 0.073(1) Cu2: U33 0.014(1) 0.013(1) Cu2: U12 −0.054(2) −0.051(2) Sb1: U11 = U22 = U33 0.009(1) 0.0090(8) Sb1: U12 0.001(1) 0.0001(9) S1: U11 = U22 0.011(1) 0.013(1) S1: U33 0.011(3) 0.010(2) S1: U12 −0.0008(19) −0.002(1) S1: U13 = U23 0.001(1) 0.001(1) S2: U11 = U22 = U33 0.020(3) 0.021(3)
3. Sample Environment Besides the routine sample environments, such as closed-cycle refrigerators (CCR) for 4–800 K, permanent magnet sets (up to 1 T), electric field options (up to 11 kV/mm), and clamp CuBe Crystals 2019, 9, 5 6 of 9
Crystals 2018, 8, x FOR PEER REVIEW 6 of 9 pressure cells (up to 2 GPa), that can be run in the four-circle goniometer mode, which enables cellsfull access(up to to2 GPa), reciprocal that can space, be therun Anger in the camerafour‐circle detector goniometer brings mode, other extreme which enables sample full environment access to reciprocalequipment space, (Figure the4 )Anger that are camera only alloweddetector tobrings tilt a other few degreesextreme or sample not allowed environment to tilt atequipment all, such (Figureas ultra-low-temperature 4) that are only allowed down to to tilt 50 mK,a few a degrees high magnetic or not allowed field up to tilt 8 T, at and all, high such pressure as ultra‐ uplow to‐ temperature45 GPa, for single-crystaldown to 50 mK, neutron a high diffraction. magnetic Thefield large up to 2D 8 AngerT, and camerahigh pressure detector up covers to 45 50GPa,◦ in for the singlevertical‐crystal and can neutron reach enoughdiffraction. out-of-plane The large reflections 2D Anger to camera determine detector structures covers for 50 these° in the extreme vertical sample and canenvironment reach enough conditions. out‐of‐plane reflections to determine structures for these extreme sample environment conditions.
(a) (b) (c)
FigureFigure 4. 4. (a()a )A A cryostat cryostat used used for for reaching reaching a a dilution dilution refrigerator refrigerator temperature temperature of of 50 50 mK mK and and (b (b) )a a cryomagnetcryomagnet used used for for reaching reaching 0–6 0–6 T T are are installed installed at at HB HB-3A‐3A in in two two-axis‐axis mode mode to to do do single single-crystal‐crystal neutronneutron diffraction. diffraction. (c ()c )The The Diamond Diamond Anvil Anvil Cell Cell (DAC) (DAC) mounted mounted at at the the cold cold head head of of a a closed closed-cycle‐cycle refrigeratorrefrigerator (CCR) (CCR) in in the the four four-circle‐circle mode. mode.
HighHigh pressure pressure studies studies have beenbeen performedperformed onon a a Ba Ba0.40.4SrSr1.61.6Mg2Fe1212OO2222 hexaferritehexaferrite crystal crystal that that presentspresents a a new new magnetoelectric magnetoelectric coefficient coefficient record record for for single single-phase‐phase materials materials [15] [15 ]by by using using Diamond Diamond ® AnvilAnvil Cells Cells (DACs) (DACs) that that were were designed designed at at ORNL ORNL [16,17]. [16,17]. Both Both polycrystalline polycrystalline diamond diamond (Versimax (Versimax®) ) ® andand single single-crystal‐crystal diamond diamond anvil anvil cells cells have have been been used. used. While While the the setup setup for for the the Versimax® Versimax cellcell is is limitedlimited to to 10 10 GPa, GPa, the the setup setup used used for for the the single single-crystal‐crystal diamond diamond anvil anvil cell cell (6 (6 mm mm anvils, anvils, 2 2 mm mm culet, culet, steelsteel gasket) gasket) is is capable capable of ofsignificantly significantly higher higher pressures pressures and andhas reached has reached 45 GPa 45 in GPa the inpast the [17]. past With [17]. theWith single the single-crystal‐crystal DAC, DAC, we can we precisely can precisely calibrate calibrate the pressure the pressure with with the ruby the ruby fluorescence fluorescence method. method. A 3 thinA thin hexaferrite hexaferrite sample sample (with (with a crystal a crystal dimension dimension of 0.7 of × 0.70.7 ×× 0.10.7 mm× 0.13) was mm loaded) was loadedinside the inside gasket the chambergasket chamber (1 mm diameter, (1 mm diameter, 0.2 mm 0.2 height) mm height) with glycerin with glycerin as the aspressure the pressure transmission transmission medium. medium. The pressureThe pressure was calibrated was calibrated by the by ruby the fluorescence ruby fluorescence method method at room at roomtemperature temperature for each for loading each loading step. Figurestep. Figure5 shows5 showsthe (220) the peak (220) change peak changebetween between the low pressure the low pressure of 0.2 GPa of (i.e., 0.2 GPathe locking (i.e., the pressure) locking andpressure) the highest and the pressure highest of pressure 7.3 GPa. of 7.3Using GPa. glycerin Using glycerinas the pressure as the pressure medium medium provides provides a better a hydrostaticbetter hydrostatic pressure pressure on the oncrystal the crystalcompared compared to that tousing that lead using as lead the aspressure the pressure medium medium [16], so [16 it], enablesso it enables studies studies under under a higher a higher pressure pressure of 7.3 GPa, of 7.3 the GPa, highest the highest pressure pressure that has that been has reached been reached so far atso HB far‐3A. at HB-3A. In principle, In principle, higher higherpressures pressures would would be possible; be possible; however, however, in this in particular this particular case, case,the samplethe sample did didnot notmaintain maintain its single its single-crystal‐crystal character character upon upon a further a further pressure pressure increase, increase, which which was was likelylikely due due to to the the non non-hydrostatic‐hydrostatic pressure pressure above above 7.3 7.3 GPa. GPa. To reach To reach a higher a higher pressure pressure than than 10 GPa, 10 GPa, we needwe need to reduce to reduce the thecrystal crystal height height to ~0.07 to ~0.07 mm mm (while (while keeping keeping the the lateral lateral dimensions) dimensions) and and using using gas gas pressure transmitting, which in principle allows for ~45 GPa while maintaining detectability on the beamline. So far, the high‐pressure experiments are only used for qualitative studies because neutron absorption caused by the gasket and the pressure medium varies with pressure. It requires more
Crystals 2019, 9, 5 7 of 9 pressure transmitting, which in principle allows for ~45 GPa while maintaining detectability on the beamline. So far, the high-pressure experiments are only used for qualitative studies because neutron absorption caused by the gasket and the pressure medium varies with pressure. It requires more Crystals 2018, 8, x FOR PEER REVIEW 7 of 9 calibration with several standard crystals, and various pressure mediums use high-pressure diffraction for crystallographic purposes.
(a) (b) (c)
FigureFigure 5. 5. HighHigh pressure pressure on on the the hexaferrite hexaferrite crystal crystal with with DAC. DAC. The The peak peak signal signal at at (2 (2 2 2 0) 0) captured captured by by thethe Camera Camera-I‐I detector detector under under pressure: pressure: ( (aa)) 0.2 0.2 GPa GPa and and ( (bb)) 7.3 7.3 GPa. GPa. Radial Radial scans scans at at (2 (2 2 2 0) 0) under under a a pressurepressure of of 0.2 0.2 GPa GPa (blue (blue squares) squares) and and 7.3 7.3 GPa GPa (red (red do dots).ts). The The higher higher background background at 7.3 at 7.3 GPa GPa is due is due to theto the pressure pressure-induced‐induced Bragg Bragg peak peak shift, shift, which which now now overlaps overlaps with with a broadened a broadened powder powder peak peak from from the gasket.the gasket. When When the theBragg Bragg peak peak overlaps overlaps with with powder powder lines lines of of the the sample sample environment, environment, the the peak peak integrationintegration cancan bebe done done through through the the rocking-curve rocking‐curve scans scans as shown as shown in (c ),in where (c), where the background the background caused causedby the powderby the powder scattering scattering is uniform is uniform and can and be properlycan be properly subtracted. subtracted.
4.4.Polarized Polarized Neutron Neutron Diffraction Diffraction 7 2 BesidesBesides the the high high flux flux (2 (2 × ×10710 n/cmn/cm2/s) and/s) the and high the‐resolution high-resolution modes modes (δd/d = ( δ2%)d/d [2]= 2%)for single [2] for‐ crystalsingle-crystal neutron neutron diffraction, diffraction, HB‐3A HB-3A DEMAND DEMAND also alsohas hasadded added a new a new capability capability for for half half-polarized‐polarized neutronneutron diffraction diffraction with with an an S S-bender‐bender supermirror supermirror polarizer. polarizer. Again Again due due to to the the large large high high-resolution‐resolution 2D2D Anger Anger camera camera detector, detector, we we can can easily easily mea measuresure the the flipping flipping ratios ratios by by snapshotting snapshotting each each reflection reflection withwith spin up/down neutrons. neutrons. The The extreme extreme sample sample environments environments can can be be used used for for half half-polarized‐polarized µ neutronneutron diffraction, diffraction, too. The The resolution resolution of of 0.01 0.01 μB ofof a a moment moment size size for for ferromagnetism ferromagnetism is is the the best best we we havehave determined determined so so far. far. We We are are still still commissioning commissioning other other polarizers polarizers for for shorter shorter wavelength wavelength neutrons, neutrons, 3 includingincluding a a 3HeHe-polarizer‐polarizer and and supermirror supermirror bender bender polarizers. The The capabilities capabilities of of measuring measuring spin spin densitydensity maps maps and and local local site site magnetic magnetic susceptibility susceptibility or or atomic atomic magnetic magnetic susceptibility susceptibility are are in in active active development.development. Further Further details details will will be be reported reported in in future future works. works.
5.5.Conclusions Conclusions AfterAfter the full detector andand fullfull capabilitycapability of of polarized polarized neutron neutron diffraction diffraction are are installed, installed, the the HB-3A HB‐ 3Awill wi havell have migrated migrated away away from from its its traditional traditional four-circle four‐circle setup setup and and becomebecome anan extreme sample sample environmentenvironment magnetic magnetic single-crystalsingle‐crystal neutronneutron diffractometer, DEMAND, that is fully suitable suitable for for studyingstudying material material science, science, especially especially quantum quantum materials, materials, condensed condensed matter matter physics, physics, solid solid state state chemistry,chemistry, mineralogy, mineralogy, and and other other small small molecular molecular crystallography crystallography and and magnetism. magnetism. Table Table 2 lists2 lists the insttherument instrument parameters parameters as a assummary a summary for DEMAND. for DEMAND.
Table 2. The DEMAND thermal single‐crystal neutron diffractometer.
Monochromator Double‐Focusing Silicon Incident wavelengths 1.008 Å Si‐331; 1.550 Å Si‐220; 2.548 Å Si‐111; 2D Anger camera (SiPM) Magnetic‐field insensitive (tested at 300 Gauss) Detector Size: 348 × 348 mm2 (50° × 50°) at SDD = 300 mm; Pixel resolution: 0.65 mm Four‐circle mode with a CCR: −27° < 2θ (scattering angle) < 155°; −40° < ω (sample table) < 45° Diffractometer angles −110° < χ (tilt) < 110°; −181° < ϕ (sample rotation motor) < 181° Two‐axis mode with cryostat or cryomagnet: Crystals 2019, 9, 5 8 of 9
Table 2. The DEMAND thermal single-crystal neutron diffractometer.
Monochromator Double-Focusing Silicon Incident wavelengths 1.008 Å Si-331; 1.550 Å Si-220; 2.548 Å Si-111; 2D Anger camera (SiPM) Magnetic-field insensitive (tested at 300 Gauss) Detector Size: 348 × 348 mm2 (50◦ × 50◦) at SDD = 300 mm; Pixel resolution: 0.65 mm Four-circle mode with a CCR: −27◦ < 2θ (scattering angle) < 155◦; −40◦ < ω (sample table) < 45◦ −110◦ < χ (tilt) < 110◦; −181◦ < φ (sample rotation motor) < 181◦ Diffractometer angles Two-axis mode with cryostat or cryomagnet: −27◦ < 2θ < 155◦; −177◦ < ω < 163◦ −5◦ < ν (tilt) < 5◦; −181◦ < φ (sample stick motor) < 181◦ Sample-Detector distance (SDD) 200–400 mm Maximum flux at sample 2.2 × 107 n/cm2/s Highest resolution δd/d > 0.3% S-bender supermirror: polarization ratio >95% for λ = 2.548 Å Polarizers 3He polarizer 90% for λ = 1.550 Å Four-circle mode with a CCR: 4 K < T < 800 K; 0 < H < 1 T; 0 < P < 40 GPa; 0 < E < 104 V/mm; Sample environment Two-axis mode with cryostat or Furnace or cryomagnet: 0.05 K < T < 1800 K; 0 < H < 8 T; 0 < P < 45 GPa; 0 < E < 11 kV/mm;
Author Contributions: Conceptualization, H.C., B.C.C., and K.M.A.; methodology, H.C., B.C.C., K.M.A., Y.W., R.A.R., W.Z., R.G., J.H., B.H., J.M., and G.W.L.; software, W.Z. and R.G.; validation, H.C., B.C.C., and K.M.A.; formal analysis, H.C., B.C.C., and Y.W.; investigation, H.C., B.C.C., K.M.A., Y.W., R.A.R., J.H., B.H., and J.M.; resources, H.C., B.C.C., K.M.A., R.A.R., J.H., B.H., and G.W.L.; writing—original draft preparation, H.C.; writing—review and editing, H.C., B.C.C., K.M.A., Y.W., R.A.R., W.Z., R.G., J.H., B.H., J.M., and G.W.L.; visualization, H.C. and Y.W.; supervision, H.C. and B.C.C. Funding: The research using polarized neutron diffraction and high pressure is supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Early Career Research Program Award KC0402010, under Contract DE-AC05-00OR22725. This research used resources at the High Flux Isotope Reactor, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. Acknowledgments: We thank Cornelius Donahue, Christopher Montcalm, and Theodore Visscher for detector development, Van Graves, Jonathan Smith, and Mike Harrington for instrument upgrade support; Matthew Collins, Cory Fletcher, Tyler White, and Christopher M. Redmon for supporting the ultra-low temperature and cryomagnet experiments, Mark J. Loguillo and Gerald M. Rucker for supporting DAC high-pressure loading, Harish Agrawal, Doug Armitage, and John Wenzel for sample environment development, Gary A. Taufer and Larry R. Senesac for SPICE support, and Mike Hittman for machining support. Conflicts of Interest: The authors declare no conflict of interest.
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