| 1. |
- Potapkin, V., et al.
(author)
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Magnetic interactions in NiO at ultrahigh pressure
- 2016
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In: PHYSICAL REVIEW B. - : AMER PHYSICAL SOC. - 2469-9950. ; 93:20, s. 201110-
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Journal article (peer-reviewed)abstract
- Magnetic properties of NiO have been studied in the multimegabar pressure range by nuclear forward scattering of synchrotron radiation using the 67.4 keV Mossbauer transition of Ni-61. The observed magnetic hyperfine splitting confirms the antiferromagnetic state of NiO up to 280 GPa, the highest pressure where magnetism has been observed so far, in any material. Remarkably, the hyperfine field increases from 8.47 T at ambient pressure to similar to 24 T at the highest pressure, ruling out the possibility of a magnetic collapse. A joint x-ray diffraction and extended x-ray-absorption fine structure investigation reveals that NiO remains in a distorted sodium chloride structure in the entire studied pressure range. Ab initio calculations support the experimental observations, and further indicate a complete absence of Mott transition in NiO up to at least 280 GPa.
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| 2. |
- Sergueev, I., et al.
(author)
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Effect of pressure, temperature, fluorine doping, and rare earth elements on the phonon density of states of LFeAsO studied by nuclear inelastic scattering
- 2013
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 87:6
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Journal article (peer-reviewed)abstract
- We have performed systematic studies of the lattice dynamics in LFeAsO (L = La, Ce, Pr, Nd, Sm) in the parent and in the similar to 10% F-doped compounds as a function of pressure and temperature. We have found that the modifications in the partial Fe density of phonon states are mainly governed by the Fe-As bond length. The change of this bond length explains the change of the Fe density of phonon states above 25 meV. We further observe anomalies in the behavior of the phonon mode near 16 meV. In the parent phase, this mode softens anomalously upon cooling through the structural phase transition. Upon F doping, this mode hardens indicating a strong electron-phonon coupling. This suggests that the corresponding phonons play an important role in the competition between superconductivity and magnetism in these materials. DOI: 10.1103/PhysRevB.87.064302
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