[{"type":"speech","title":"Thermodynamic properties of the magnetic layered compound BaNi\u2082V\u2082O\u2088","issued":{"date-parts":[["2006"]]},"author":[{"family":"Knafo","given":"W."},{"family":"Drobnik","given":"S."},{"family":"Grube","given":"K."},{"family":"L\u00f6hneysen","given":"H. von"},{"family":"Meingast","given":"C."},{"family":"Popovich","given":"P."},{"family":"Schweiss","given":"P."},{"family":"Wolf","given":"T."}],"note":"Internat.Conf.on Strongly Correlated Electron Systems (SCES '05), Wien, A, July 26-30, 2005 DPG Spring Meeting of the Divison Condensed Matter, 21st General Conf.of the Condensed Matter Division of the European Physical Society, Dresden, March 26-31, 2006 Verhandlungen der Deutschen Physikalischen Gesellschaft, R.6, B.41(2006) MA 12.4 Internat.Conf.on Magnetism (ICM 2006), Kyoto, J, August 20-25, 2006 Book of Abstracts","abstract":"Magnetism\nSectional Programme Overview\nMA 12 Kondo \/ Heavy Fermions\nTime: Monday 16:30\u201317:45\nMA 12.1 Mon 16:30 HSZ 403\nMagnetic ground state of the frustrated one dimensional binary compound CuCl2 \u2014 \u2022Michael Banks1 , Reinhard K Kremer1 , and Bachir Ouladdiaf2 \u2014 1 MPI-FKF, 70569 Stuttgart \u2014 2 ILL\nGrenoble, CEDEX 9\nHistorically, the binary CuCl2 and the structurally similar CuBr2 are\namong the very \ufb01rst systems the magnetic properties of which were analyzed in terms of a linear spin chain arrangements. Low-dimensional\nmagnetism with typical signatures, e.g. a broad short-range ordering\nmaxima in the susceptibility and heat capacity, have been found. The\nantiferromagnetic (afm) intra-chain exchange parameters are signi\ufb01cant\n(e.g. \u2248320K for CuBr2 ). However, both systems are far from representing ideal one-dimensional magnets as must be concluded from the\nrather high transition temperatures to long-range ordering (e.g. 24 K for\nCuCl2 ) indicating appreciable inter-chain coupling. To the best of our\nknowledge, the magnetic structures of CuCl2 and CuBr2 remain unsolved\nuntil now. We studied the afm ordering of CuCl2 and CuBr2 in detail by\nneutron powder di\ufb00raction using ILL\u2019s high \ufb02ux powder di\ufb00ractometer\nD20 in its high resolution option. Using single crystals of CuCl2 , we used\nthe 4-circle di\ufb00ractometer D10 also at the ILL to conclusively solve the\nmagnetic structure. The magnetic structure of CuCl2 will be presented as\nshowing helicoidal ordering along the chain direction with an incommensurate propagation vector \u03c4 = [0.5,0.224,0]. The magnetic phase diagram\nwill be presented showing a spin-\ufb02op phase along the chain direction at\nH SF \u2248 4T.\nMA 12.2 Mon 16:45 HSZ 403\nHigh-resolution Fermi-Edge and energy dependent photoemission spectra of Fe1\u2212x Cox Si \u2014 \u2022D. Zur1 , I. Jursic1 , D. Menzel1 ,\nL. Patthey2 , and J. Schoenes1 \u2014 1 Institut f\u00a8r Physik der Kondenu\nThe interest on FeSi is renewed because of similarities with some rareearth compounds known as Kondo insulators. In spite of several photoemission investigations, the size of the gap is still not clear. In addition,\nthe in\ufb02uence on the electronic structure by doping with a 3d transition\nmetal is interesting due to the changes in electronic and magnetic properties. We present high resolution photoemission spectra at 11 K of the\nFermi edge of Fe1\u2212x Cox Si crystals with 0, 5 and 20 at.% Co, using synchrotron radiation at the SLS. Photon energies of 21.2 eV and 40.8 eV\nhave been used. A gap of about 80 meV has been found, which is consistent with some theoretical predictions. This gap closes with increasing\nCo concentrations. Furthermore, changes in the electronic structure owing to di\ufb00erent Co concentrations have been studied with angle- and\nphotoenergy-resolved photoemission.\nMA 12.3 Mon 17:00 HSZ 403\nField-induced parity breaking in isotropic frustrated spin chains\n\u2014 \u2022Oleksiy Kolezhuk1,2 and Temo Vekua3 \u2014 1 Physics Dept.., Harvard University, Cambridge MA 02138, USA \u2014 2 Inst. f. Theor. Physik,\nUniv. Hannover, 30167 Hannover, Germany \u2014 3 Univ. Louis Pasteur,\nLab. de Physique Theorique, 67084 Strasbourg Cedex, France\nIt is argued that an external magnetic \ufb01eld applied to an isotropic\nzigzag spin chain with an arbitrary spin S and antiferromagnetic nearestneighbor and next-nearest-neighbor exchange couplings J1 and J2 induces\na quantum phase transition into a phase with spontaneously broken parity, characterized by long-range ordering of vector chirality. To show\nthat, we use a bosonization approach for S = 1\/2 and S = 1, valid in\nthe limit of a weak zigzag interaction J1 \/J2\n1, as well as an e\ufb00ective\nlarge-S theory applicable in the vicinity of the saturation \ufb01eld. Relevance\nto real materials and the possibility of experimental observation of chiral\nphases are discussed.\nMA 12.4 Mon 17:15 HSZ 403\nBaNi2 V2 O8 \u2014 \u2022William Knafo1,2 , Stephanie Drobnik1,2 , Kai\n\u00a8\nPaul Popovich1 , Peter Schweiss1 , and Thomas Wolf1 \u2014\n1\nRoom: HSZ 403\nBaNi2 V2 O8 is a quasi two-dimensional magnetic system which consists\nof a planar honeycomb arrangement of spin-1 ions of Ni2+ . Although a\nsmall inter-plane interaction leads to three-dimensional magnetic order\nbelow TN = 47 K, this system has been recently proposed as a candidate\nfor a two-dimensional XY magnetic model where a Kosterlitz-Thouless\ntransition should occur [1]. To test this scenario, we have grown large\nsingle crystals of BaNi2 V2 O8 and have investigated their thermodynamic\nproperties. We present here speci\ufb01c heat, thermal expansion, magnetostriction, and magnetization measurements, which were carried out for\ntemperatures T between 3 and 300 K and magnetic \ufb01elds H up to 14\nT. The main features of the resulting (H, T) phase diagram are (i) an\nincrease of TN when the \ufb01eld is applied in the plane and (ii) a cross-over\nto a \u201dspin-\ufb02op\u201dphase below TN for \ufb01elds higher than HSF \u2248 1.4 T. The\nanisotropy of the magnetic moments and the dimensionality of their interactions will be considered carefully to discuss if a two dimensional XY\nmodel is relevant or not for this system.\n[1] N. Rogado et al., Phys. Rev. B 65, 144443 (2002).\nMA 12.5 Mon 17:30 HSZ 403\nBose glass vs. Mott glass in site-diluted S=1 Heisenberg antiferromagnets \u2014 \u2022Tommaso Roscilde1,2 and Stephan Haas2 \u2014 1 MaxPlanck-Institut fuer Quantenoptik, Garching (Germany) \u2014 2 University\nof Southern California, Los Angeles\nMaking use of large-scale quantum Monte Carlo simulations, we investigate the ground-state phase diagram of the square-lattice S=1 Heisenberg antiferromagnet with strong single-ion anisotropy and in presence\nof site dilution of the magnetic lattice. Mapping the spins onto HolsteinPrimako\ufb00 bosons, the single-ion anisotropy is seen to play the role of\na repulsive on-site potential for the bosons. The clean limit of the\nmodel shows an anisotropy-driven quantum phase transition from an\nXY ordered (super\ufb02uid) phase to a quantum disordered (Mott insulating) phase. A similar transition is also driven by the application of a\nuniform \ufb01eld on the disordered state. Adding site dilution to the model,\nthe non-trivial interplay between quantum \ufb02uctuations and lattice randomness gives rise to a novel quantum-disordered Mott glass phase in\nzero \ufb01eld, with a gapless spectrum and yet a vanishing uniform susceptibility. Upon applying a \ufb01eld, such phase is turned into a Bose glass, with\ngapless spectrum and \ufb01nite susceptibility. The above picture is directly\nrelevant for experiments on doped quasi-low-dimensional Ni compounds,\nas the recently investigated NiCl2 -4SC(NH2 )2 (V.S. Zapf et al., condmat\/0505562).","kit-publication-id":"240063932"}]