Survey of background scattering from materials found in small-angle neutron scattering

Barker, J. G.; Mildner, D. F. R.

doi:10.1107/s1600576715010729

Cited by 34 publications

(27 citation statements)

References 46 publications

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“…2(d,e), calculations based on ref. 28 and literature data for LaCoO 3 indicate a qualitatively different form than the measured T dependence, particularly below ∼100 K.…”

Section: )) and M/h(t)contrasting

confidence: 64%

Neutron-scattering-based evidence for interacting magnetic excitons inLaCoO3

et al. 2015

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Recent progress with the thermally-driven spin-state crossover in LaCoO 3 has made it increasingly apparent that the nominally non-magnetic low spin ground state of this material actually hosts novel defect-based magnetism. This is investigated here via a small-angle neutron scattering (SANS) study of LaCoO 3-δ crystals. The results provide: (i) the surprising finding that the spin-state crossover is clearly reflected in SANS via quasielastic/inelastic scattering from paramagnetic spin fluctuations/excitations, and (ii) evidence for the formation, likely around oxygen defects, of local entities known as magnetic excitons. The latter generate distinct magnetic scattering below 60 K, providing valuable quantitative information on exciton densities and interactions. Potential relevance to the unexpected ferromagnetism recently discovered in epitaxial LaCoO 3 films is discussed.PACS Nos: 75.47.Lx, 75.30.Wx, Corresponding author: CL (leighton@umn.edu) 2 Magnetism in LaCoO 3 has attracted attention and controversy for almost 50 years, largely due to the only marginal dominance of the crystal field splitting of t 2g and e g states over the Hund exchange energy [1,2]. A low spin (LS, t 2g 6 e g 0 , S = 0) configuration is thus observed in the ground state, but is stable only to ∼30 K, at which point excited spin-states are gradually populated [1][2][3][4][5][6][7][8][9][10][11][12]. These excited states can be simplistically described as intermediate spin ( Despite these challenges, substantial recent progress has been achieved. This encompasses:(i) Increased recognition that characterization of excited states as atomic-like "IS" or "HS" is likely misleading due to significant spin-orbit coupling [15] and ; (ii) A suite of experiments using electron spin resonance [6,11], X-ray absorption spectroscopy/magnetic circular dichroism [7], and inelastic neutron spectroscopy (INS) [8,9], that consistently identify a zero-field-split triplet as the first excited state; (iii) Direct measurement of both a 0.6 meV excitation associated with this triplet [8,9] and a g-factor of 3-3.5 [6,11]; and (iv) Consistent interpretation of these results in terms of a spin-orbit triplet excited state [6,8,9,11,15]. While the understanding of the spin-state problem in LaCoO 3 thus remains incomplete, it is nevertheless advancing. [27]. Noteworthy in comparison to conventional magnetic polarons is that these excitons / spin-state polarons form as the host lattice crosses over to an S = 0 ground state; they can thus exist in a non-magnetic (as opposed to para-or antiferro-magnetic) matrix.Here, a study of the magnetism of LaCoO 3 crystals using small-angle neutron scattering (SANS) is reported. The magnetic SANS is found to have two contributions: A low scattering wavevector (q) part with strong q dependence that turns on below 60 K, and a higher q part with 4 negligible q dependence that increases gradually on warming above 30 K. The latter is shown to be due to the spin-state crossover, which SANS is demonstrated to be sensitive to via the qua...

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“…2(d,e), calculations based on ref. 28 and literature data for LaCoO 3 indicate a qualitatively different form than the measured T dependence, particularly below ∼100 K.…”

Section: )) and M/h(t)contrasting

confidence: 64%

Neutron-scattering-based evidence for interacting magnetic excitons inLaCoO3

et al. 2015

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“…These scaled data coincide with the measured data. The scaling relation (30) might not hold for unconventional SANS processes, such as multiple Bragg scattering (MBS), which might contribute significantly to the SANS cross section (Barker & Mildner, 2015). 5(b), where again the scaled and measured data coincide.…”

Section: Resultsmentioning

confidence: 99%

“…The absorption of the -Fe 2 O 3 powder was included in these plots, although it is small and has no visible effect ( th = 0.10 cm À1 for bulk -Fe 2 O 3 ; the powder density is roughly 40% less). The scaling relation (30) might not hold for unconventional SANS processes, such as multiple Bragg scattering (MBS), which might contribute significantly to the SANS cross section (Barker & Mildner, 2015). Our analysis technique is also valid for such unconventional SANS processes, if the scaling equation (30) holds.…”

Section: Resultsmentioning

confidence: 99%

Neutron Larmor diffraction on powder samples

et al. 2020

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A hitherto unrecognized resolution effect in neutron Larmor diffraction (LD) is reported, resulting from small-angle neutron scattering (SANS) in the sample. Small distortions of the neutron trajectories by SANS give rise to a blurring of the Bragg angles of the order of a few hundredths of a degree, leading to a degradation of the momentum resolution. This effect is negligible for single crystals but may be significant for polycrystalline or powder samples. A procedure is presented to correct the LD data for the parasitic SANS. The latter is accurately determined by the SESANS technique (spin-echo small-angle neutron scattering), which is readily available on Larmor diffractometers. The analysis technique is demonstrated on LD and SESANS data from -Fe 2 O 3 powder samples. The resulting d-spacing range agrees with experimental data from high-resolution synchrotron radiation powder diffraction on the same sample. research papers J. Appl. Cryst. (2020). 53, 88-98 Thomas Keller et al. Neutron Larmor diffraction on powder samples 89

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“…One can compare the results of the small-angle scattering with other contributions that have been described by Barker & Mildner (2015), such as those of the detector windows. The relatively high scattering for the aperture made with the natural abundance B 4 C has a variation of intensity at small Q of approximately 1/Q 4 .…”

Section: Discussionmentioning

confidence: 99%

Boron carbide composite apertures for small-angle neutron scattering made by three-dimensional printing

Olsson

Rennie

2016

J Appl Crystallogr

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Apertures for small-angle neutron scattering prepared from a boron carbide/ polymer composite have been made by three-dimensional printing using fused filament fabrication. Use of enriched 10 B 4 C gives higher absorption and much lower parasitic scattering than natural B 4 C. The simple fabrication, the capability to replace toxic and environmentally hazardous materials such as cadmium, and the possibility to diminish the secondary background of -radiation are attractive features of use of these materials. Complex shapes, apart from apertures, can be fabricated readily with this composite, for example, to make shielding for instrument components and masks used to calibrate detectors.

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Survey of background scattering from materials found in small-angle neutron scattering

Cited by 34 publications

References 46 publications

Neutron-scattering-based evidence for interacting magnetic excitons inLaCoO3

Neutron-scattering-based evidence for interacting magnetic excitons inLaCoO3

Neutron Larmor diffraction on powder samples

Boron carbide composite apertures for small-angle neutron scattering made by three-dimensional printing

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