投稿者 : webmaster 投稿日時： 2012-11-20 19:00:00 (4773 ヒット)
Electron has a feature of magnet, so called "spin". In magnetic materials, huge number of electronic spins spontaneously align their directions resulting in "ordered magnetic states". Ordinary magnets typically contain transition elements and/or rare earth elements. In the past decades, great effort has been made to realize the magnetic ordering in materials comprising only nonmagnetic elements. One fascinating example is three dimensionally arrayed alkali-metal nanoclusters in zeolite crystals. Figure (a) shows a schematic illustration of the crystal structure of sodalite which is a kind of zeolites. In sodalite, nano-sized cages are arrayed in a body-centered-cubic structure. We can "dope" a sodium atom into each cage, and an s-electron provided by the guest sodium atom is accommodated in the cage as shown in Fig. (b). Due to an exchange interaction between the adjacent s-electrons through the window of the cage, antiferromagnetic ordering is realized. Recently, we, a group from Osaka University, succeeded in detecting directory the magnetic ordering of this material by using a neutron diffraction for the first time. The experiments were performed using the spectrometer PONTA.The spatial distribution of the s-electron spin was also examined, and it was confirmed that the s-electron delocalized over nanometer size in the cage is responsible for the magnetic ordering. This work is published in Physical Review Letters on 17 Oct. 2012.
投稿者 : taku 投稿日時： 2010-09-13 12:19:54 (8791 ヒット)
An electron is a magnet. However, the magnetic moment of the electron can take only the two states, up and down, which is in contrast to the real-life magnet which can have any direction. This degree of freedom, up and down states, is called "spin". When the two spins interact with each other antiferromagnetically, surprisingly they couple, and disappear (formation of singlet). In strongly frustrated lattice as kagome lattice, this coupling cannot be formed trivially; up spin cannot select which down spin to couple... Consequently, the singlet state starts to move around the lattice; the resonating-valence-bond state. When a weak breaking of the complete frustration is introduced, the singlet solidifies, resulting in the valence-bond-solid state. Of course, the spins hide themselves by forming singlet pairs, so they are not easy to be seen experimentally. We, a team from ISSP, Tokyo Tech. and Tokyo Univ. of Science, uses neutron scattering to "see" the hidden state by exciting the singlet ground state into triplet excited state. In this experiment, we confirm the pinwheel VBS state in the model kagome antiferromagnet Rb2Cu3SnF12. This result is published in Nature Physics on 2010/09/12. Detail in Japanese can be found elsewhere.