Small angle neutron scattering measurements have been performed to study the thermodynamic stability of skyrmion-lattice phases in Cu2OSeO3. We found that the two distinct skyrmion-lattice phases [SkX(1) and SkX(2) phases] can be stabilized through different thermal histories; by cooling from the paramagnetic phase under finite magnetic field, the SkX(2) phase is selected. On the other hand, the 30• -rotated SkX(1) phase becomes dominant by heating the sample from the ordered conical phase under finite field. This difference in stabilization is surprisingly similar to the irreversibility observed in spin glasses. The zero-field cooling results in the co-existence of the two phases. It is further found that once one of the skyrmion-lattice phases is formed, it is hardly destabilized. This indicates unusual thermal stability of the two skyrmion-lattice phases originating from an unexpectedly large energy barrier between them.
Centimetre-sized single crystals of high-quality CaBaCo 2 Fe 2 O 7 were synthesized by the optical floating zone technique. The metal-to-metal stoichiometry and oxygen content were confirmed by spectroscopy and thermal reduction experiments. The hexagonal symmetry P6 3 mc (No. 186) well describes the powder X-ray and neutron diffraction as well as single-crystal neutron diffraction at all measured temperatures. This symmetry is also consistent with optical second harmonic generation data obtained between 10 and 295 K. However, a satisfactory structure description from single-crystal neutron diffraction data needs an oxygen split position. Specific heat, magnetic susceptibility and powder neutron diffraction data indicate a magnetic phase transition at T N = 159 K to an antiferromagnetic ground state, but with a persisting hexagonal symmetry and intrinsic geometric frustration.research papers
The hexagonal swedenborgite, CaBaCo 2 Fe 2 O 7 , is a chiral frustrated antiferromagnet, in which magnetic ions form alternating Kagome and triangular layers. We observe a long range √ 3 × √ 3 antiferromagnetic order setting in below TN = 160 K by neutron diffraction on single crystals of CaBaCo 2 Fe 2 O 7 . Both magnetization and polarized neutron single crystal diffraction measurements show that close to TN spins lie predominantly in the ab-plane, while upon cooling the spin structure becomes increasingly canted due to Dzyaloshinskii-Moriya interactions. The ordered structure can be described and refined within the magnetic space group P 31m . Diffuse scattering between the magnetic peaks reveals that the spin order is partial. Monte Carlo simulations based on a Heisenberg model with two nearest-neighbor exchange interactions show a similar diffuse scattering and coexistence of the √ 3 × √ 3 order with disorder. The coexistence can be explained by the freedom to vary spins without affecting the long range order, which gives rise to ground-state degeneracy. Polarization analysis of the magnetic peaks indicates the presence of long-period cycloidal spin correlations resulting from the broken inversion symmetry of the lattice, in agreement with our symmetry analysis.
Abstract. Rubidium guanidinate, RbCN 3 H 4 , is the first example of a new class of compounds containing the unsubstituted guanidinate anion CN 3 H 4 -. While the first crystal-structure determination was based on powder X-ray diffraction, neutron powder and single-crystal X-ray diffraction have now been utilized to improve the previous structural model, in particular with respect to experimentally localizing the hydrogen positions, which were so far derived from density-functional
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