Polarization anisotropy of X-ray atomic factors and `forbidden' resonant reflections

Дмитриенко, В. Е.; Ishida, Kohtaro; Kirfel, Α.; Овчинникова, Е. Н.

doi:10.1107/s0108767305018209

Cited by 125 publications

(86 citation statements)

References 93 publications

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“…The resonant scattering process adopted is a rather exotic one, involving pure electric quadrupole events (that is, beyond the usual dipole approximation). However, in recent years, such phenomena have been studied in detail and are now extremely well understood 19,20 . Its phase and amplitude vary rapidly with photon energy, being significant only very close to the Fe K X-ray absorption pre-edge energy of 7.11 keV, and it has a complex dependence on both photon polarization and the azimuthal rotation of the sample about the normal to the diffracting planes (ψ-angle).…”

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confidence: 99%

Measuring the Dzyaloshinskii–Moriya interaction in a weak ferromagnet

et al. 2014

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Magnetism-the spontaneous alignment of atomic moments in a material-is driven by quantum mechanical exchange interactions that operate over interatomic distances. Some magnetic interactions cause 1,2 , or are caused by 3,4 , a twisting of arrangements of atoms. This can lead to the magnetoelectric e ect, predicted to play a prominent role in future technology, and to the phenomenon of weak ferromagnetism, governed by the so-called Dzyaloshinskii-Moriya interaction 5-8 . Here we determine the sign of the latter interaction in iron borate (FeBO 3 ) by using synchrotron radiation. We present a novel experimental technique based on the interference between two X-ray scattering processes, where one acts as a reference wave. Our experimental results are validated by state-ofthe-art ab initio calculations. Together, our experimental and theoretical approaches are expected to open up new possibilities for exploring, modelling and exploiting novel magnetic and magnetoelectric materials.There is considerable mystery behind the origins of complicated structures. Although the dominant short-range interactions that allow the building blocks to grow are well understood, the much more subtle forces that lead to a particular twisting at larger lengthscales, such as chiral biological molecules and liquid crystals 9 , and canted magnetic systems 3 , remain subjects of topical debate. In this Letter we seek to address this question for the case of magnetism. Our main findings are twofold: first, we demonstrate a novel and elegant experimental method for exploring magnetic materials with weak relativistic spin-orbit interactions, and second, we present a state-of-the-art quantum-mechanical many-body approach to the detailed description of such interactions in crystals. As a touchstone example we selected crystalline iron borate (FeBO 3 ), which is a strongly correlated electron system with a relatively simple crystal structure, nonetheless allowing a nontrivial canted and locally twisted magnetic ordering pattern. Taken together, these two strands demonstrate that modern condensed matter theory is capable of determining the elusive sign of the Dzyaloshinskii-Moriya interaction, and is thus able to elucidate the mechanism for coupling electric and magnetic degrees of freedom in magnetoelectric multiferroics, and to begin to predict the properties of this important class of materials.The interactions between atomic magnetic moments (or spins) are not direct, but mediated by the intervening matter. Coupling can be diminished through screening 10 , or enhanced, for example, by superexchange via oxygen atoms 11 . Moreover, the coupling is a property of the material and, according to Neumann's principle, must therefore possess all of its symmetries. The most general form of the bilinear coupling energy between two spins contains a scalar (isotropic) exchange term, exchange anisotropy (which we will neglect for the present discussion) and an antisymmetric term that reverses with permutation of the spin indices. The latter is the Dzyaloshi...

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Measuring the Dzyaloshinskii–Moriya interaction in a weak ferromagnet

et al. 2014

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“…In this framework, the atomic scattering factors should be described by using a tensorial formalism. [32][33][34] It is worth pointing out that similar azimuthal behavior can be obtained from the atomic approach given by Hannon et al, 35 but the tensorial analysis is more general and appropriate.…”

Section: Discussionmentioning

confidence: 85%

Double stripe ordering inNd0.5Sr0.5MnO3determined by resonant soft x-ray scattering

et al. 2006

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We have studied the low-temperature ordered phase of Nd 0.5 Sr 0.5 MnO 3 by resonant soft x-ray scattering at the Mn L 2,3 edges. Strong resonances were observed at ͑ 0 1 2 0 ͒ and ͑ 1 2 0 0 ͒ reflections, which are resolved in momentum space. Azimuthal scans reveal a periodicity for both resonances, the minimum intensity being almost zero. The two reflections show a very different energy dependence which extends in the whole energy region of the Mn L-edge. The ͑ 0 1 2 0 ͒ reflection originates from the anisotropy induced on the d-symmetry projected density of states owing to the local tetragonal distortion at one of the two crystallographic inequivalent Mn sites ͑the so-called Mn 3+ ions in the conventional ionic description͒. This is similar to the resonance observed at the Mn K edge. We propose that the ͑ 1 2 0 0 ͒ reflection, which has not its counterpart either on the Mn K-edge resonant scattering or on the magnetic scattering, is originated by anisotropy of the d-symmetry projected density of the so-called Mn 4+ sublattice. In this way, the latter reflection could denote a pure orbital ordering in this sublattice.

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“…Such anisotropy of anomalous scattering is, however, only significant in the near-edge region, as has been experimentally demonstrated in numerous investigations for salts and small-molecule compounds (Templeton & Templeton, 1982, 1995Kirfel et al, 1991;Dmitrienko, 1983). A comprehensive review of these studies has been presented by Dmitrienko et al (2005). Anisotropy of anomalous scattering has also been observed for selenated proteins Fanchon & Hendrickson, 1990;Bricogne et al, 2005), and in metalloproteins (Hendrickson et al, 1988).…”

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confidence: 99%

Polarization-dependence of anomalous scattering in brominated DNA and RNA molecules, and importance of crystal orientation in single- and multiple-wavelength anomalous diffraction phasing

et al. 2007

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In this paper the anisotropy of anomalous scattering at the Br K-absorption edge in brominated nucleotides is investigated, and it is shown that this effect can give rise to a marked directional dependence of the anomalous signal strength in X-ray diffraction data. This implies that choosing the correct orientation for crystals of such molecules can be a crucial determinant of success or failure when using single-and multiple-wavelength anomalous diffraction (SAD or MAD) methods to solve their structure. In particular, polarized absorption spectra on an oriented crystal of a brominated DNA molecule were measured, and were used to determine the orientation that yields a maximum anomalous signal in the diffraction data. Out of several SAD data sets, only those collected at or near that optimal orientation allowed interpretable electron density maps to be obtained. The findings of this study have implications for instrumental choices in experimental stations at synchrotron beamlines, as well as for the development of data collection strategy programs.

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Polarization anisotropy of X-ray atomic factors and `forbidden' resonant reflections

Cited by 125 publications

References 93 publications

Measuring the Dzyaloshinskii–Moriya interaction in a weak ferromagnet

Measuring the Dzyaloshinskii–Moriya interaction in a weak ferromagnet

Double stripe ordering inNd0.5Sr0.5MnO3determined by resonant soft x-ray scattering

Polarization-dependence of anomalous scattering in brominated DNA and RNA molecules, and importance of crystal orientation in single- and multiple-wavelength anomalous diffraction phasing

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