ALBERT

Description: 〈p〉Multiple-〈i〉q〈/i〉 spin order, i.e., a spin texture characterized by a multiple number of coexisting magnetic modulation vectors 〈i〉q〈/i〉, has recently attracted attention as a source of nontrivial magnetic topology and associated emergent phenomena. One typical example is the triple-〈i〉q〈/i〉 skyrmion lattice state stabilized by Dzyaloshinskii-Moriya interactions in noncentrosymmetric magnets, while the emergence of various multiple-〈i〉q〈/i〉 states of different origins is expected according to the latest theories. Here, we investigated the magnetic structure of the itinerant polar hexagonal magnet Y〈sub〉3〈/sub〉Co〈sub〉8〈/sub〉Sn〈sub〉4〈/sub〉, in which several distinctive mechanisms favoring multiple-〈i〉q〈/i〉 states are allowed to become active. Small-angle neutron-scattering experiments suggest the formation of incommensurate triple-〈i〉q〈/i〉 magnetic order with an in-plane vortex-like spin texture, which can be most consistently explained in terms of the novel four-spin interaction mechanism inherent to itinerant magnets. The present results suggest a new route to realizing exotic multiple-〈i〉q〈/i〉 orders and that itinerant hexagonal magnets, including the 〈i〉R〈/i〉〈sub〉3〈/sub〉〈i〉M〈/i〉〈sub〉8〈/sub〉Sn〈sub〉4〈/sub〉 family with wide chemical tunability, can be a unique material platform to explore their rich phase diagrams.〈/p〉

Description: Multiple- q spin order, i.e., a spin texture characterized by a multiple number of coexisting magnetic modulation vectors q , has recently attracted attention as a source of nontrivial magnetic topology and associated emergent phenomena. One typical example is the triple- q skyrmion lattice state stabilized by Dzyaloshinskii-Moriya interactions in noncentrosymmetric magnets, while the emergence of various multiple- q states of different origins is expected according to the latest theories. Here, we investigated the magnetic structure of the itinerant polar hexagonal magnet Y 3 Co 8 Sn 4 , in which several distinctive mechanisms favoring multiple- q states are allowed to become active. Small-angle neutron-scattering experiments suggest the formation of incommensurate triple- q magnetic order with an in-plane vortex-like spin texture, which can be most consistently explained in terms of the novel four-spin interaction mechanism inherent to itinerant magnets. The present results suggest a new route to realizing exotic multiple- q orders and that itinerant hexagonal magnets, including the R 3 M 8 Sn 4 family with wide chemical tunability, can be a unique material platform to explore their rich phase diagrams.

Description: Although the oxidation of water is efficiently catalysed by the oxygen-evolving complex in photosystem II (refs 1 and 2), it remains one of the main bottlenecks when aiming for synthetic chemical fuel production powered by sunlight or electricity. Consequently, the development of active and stable water oxidation catalysts is crucial, with heterogeneous systems considered more suitable for practical use and their homogeneous counterparts more suitable for targeted, molecular-level design guided by mechanistic understanding. Research into the mechanism of water oxidation has resulted in a range of synthetic molecular catalysts, yet there remains much interest in systems that use abundant, inexpensive and environmentally benign metals such as iron (the most abundant transition metal in the Earth's crust and found in natural and synthetic oxidation catalysts). Water oxidation catalysts based on mononuclear iron complexes have been explored, but they often deactivate rapidly and exhibit relatively low activities. Here we report a pentanuclear iron complex that efficiently and robustly catalyses water oxidation with a turnover frequency of 1,900 per second, which is about three orders of magnitude larger than that of other iron-based catalysts. Electrochemical analysis confirms the redox flexibility of the system, characterized by six different oxidation states between Fe(II)5 and Fe(III)5; the Fe(III)5 state is active for oxidizing water. Quantum chemistry calculations indicate that the presence of adjacent active sites facilitates O-O bond formation with a reaction barrier of less than ten kilocalories per mole. Although the need for a high overpotential and the inability to operate in water-rich solutions limit the practicality of the present system, our findings clearly indicate that efficient water oxidation catalysts based on iron complexes can be created by ensuring that the system has redox flexibility and contains adjacent water-activation sites.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Okamura, Masaya -- Kondo, Mio -- Kuga, Reiko -- Kurashige, Yuki -- Yanai, Takeshi -- Hayami, Shinya -- Praneeth, Vijayendran K K -- Yoshida, Masaki -- Yoneda, Ko -- Kawata, Satoshi -- Masaoka, Shigeyuki -- England -- Nature. 2016 Feb 25;530(7591):465-8. doi: 10.1038/nature16529. Epub 2016 Feb 10.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, Higashiyama 5-1, Myodaiji, Okazaki, Aichi 444-8787, Japan. ; SOKENDAI (The Graduate University for Advanced Studies), Shonan Village, Hayama, Kanagawa 240-0193, Japan. ; Research Center of Integrative Molecular Systems, Institute for Molecular Science, Nishigo-naka 38, Myodaiji, Okazaki, Aichi 444-8585, Japan. ; Advanced Catalytic Transformation Program for Carbon Utilization (ACT-C), Japan Science and Technology Agency, Honcho 4-1-8, Kawaguchi, Saitama 332-0012, Japan. ; Department of Theoretical and Computational Molecular Science, Institute for Molecular Science, Nishigo-naka 38, Myodaiji, Okazaki, Aichi 444-8585, Japan. ; Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, Honcho 4-1-8, Kawaguchi, Saitama 332-0012, Japan. ; Department of Chemistry, Graduate School of Science and Technology, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan. ; Department of Chemistry and Applied Chemistry, Graduate School of Science and Engineering, Saga University, Honjo-machi 1, Saga, 840-8502, Japan. ; Department of Chemistry, Faculty of Science, Fukuoka University, Nanakuma, Jonan-ku 8-19-1, Fukuoka 814-0180, Japan.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26863188" target="_blank"〉PubMed〈/a〉