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- Artyukhin, Sergey, et al.
(författare)
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Solitonic lattice and Yukawa forces in the rare-earth orthoferrite TbFeO3
- 2012
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Ingår i: Nature Materials. - 1476-4660. ; 11:8, s. 694-699
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Tidskriftsartikel (refereegranskat)abstract
- The random fluctuations of spins give rise to many interesting physical phenomena, such as the 'order-from-disorder' arising in frustrated magnets and unconventional Cooper pairing in magnetic superconductors. Here we show that the exchange of spin waves between extended topological defects, such as domain walls, can result in novel magnetic states. We report the discovery of an unusual incommensurate phase in the orthoferrite TbFeO3 using neutron diffraction under an applied magnetic field. The magnetic modulation has a very long period of 340 angstrom at 3 K and exhibits an anomalously large number of higher-order harmonics. These domain walls are formed by Ising-like Tb spins. They interact by exchanging magnons propagating through the Fe magnetic sublattice. The resulting force between the domain walls has a rather long range that determines the period of the incommensurate state and is analogous to the pion-mediated Yukawa interaction between protons and neutrons in nuclei.
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| 2. |
- Tsapatsaris, Nikolaos, et al.
(författare)
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Polymorphic drugs examined with neutron spectroscopy: Is making more stable forms really that simple?
- 2013
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 427, s. 124-128
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Tidskriftsartikel (refereegranskat)abstract
- Understanding polymorphism in pharmaceutical ingredients is a long-standing challenge in formulation science. A well-known example is paracetamol, C8H9NO2. The marketed stable form I crystallizes with corrugated molecular layers. In contrast, form II, which is thermodynamically favorable at high pressures, has relatively planar layers that can slip over each other without difficulty, but is metastable at ambient conditions. By means of inelastic neutron scattering we demonstrated that the lattice modes of form II exhibit a sudden 1 meV energy shift at 300 K under a pressure of ca 0.4 GPa. Moreover, evidence of an increase of the vibrational energy in both polymorphs was found, which was accompanied, in form I, by an unexpectedly weak increase of the tunnel splitting. These results indicate an anisotropy of the potential surface probed by the methyl rotor, and are discussed in relation to the differences of the strength of the hydrogen bond environment for each polymorph. (C) 2013 Elsevier B. V. All rights reserved.
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