Dynamic Spin Freezing in the Spin Ice Compound Dy2Ti2O7
P. Schiffera, J. Snydera, J. S. Sluskyb, R. J. Cavab
aDepartment of Physics and Materials Research Institute, Pennsylvania State University, University Park PA 16802 USA
bDepartment of Chemistry and Princeton Materials Institute, Princeton University, Princeton, NJ 08540 USA
Recent work has shown that the geometrical frustration of ice is replicated by Dy2Ti2O7, a site-ordered magnetic material in which the spins reside on a lattice of corner sharing tetrahedra and form a novel magnetic ground state known as ßpin ice" We have found a cooperative spin-freezing transition leading to the spin ice ground state in Dy2Ti2O7 which dilution studies show is associated with the development of spin-spin correlations. This transition is associated with a very narrow range of relaxation times which is more analogous to the freezing of protons in ice than spin-freezing in traditional spin glasses.
Magnetic Ordering under High Pressure in the Quantum Spin System TlCuCl3
Hidekazu Tanakaa, Kenji Gotoa, Toshio Onoa, Yoshiya Uwatokob
aDepartment of Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan
bInstitute for Solid State Physics, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
TlCuCl3 is a strongly coupled spin dimer system with the excitation gap D/kB=7.7 K. It was found that at pressure of P=10 kbar, TlCuCl3 undergoes magnetic ordering at TN » 10 K. The phase diagram for the magnetic field parallel to the [2,0,1] direction is presented.
Microscopic Magnetic Phase Separation at the Impurity Stimulated Antiferromagnetic Ordering of two Spin-Gap Systems
A.I. Smirnova, V.N. Glazkova, T Masudab, K. Uchinokurab, A.Ya. Shapiroc, L.N. Demianetsc
aP.L.Kapitza Institute for Physical Problems RAS, 117334 Moscow, Russia
bUniversity of Tokyo, Tokyo 113-8656, Japan
cA.V.Shubnikov Institute of Crystallography RAS, 117333 Moscow, Russia
ESR spectra of spin-Peierls compound CuGeO3 and Haldane magnet PbNi2V2O8, both doped with 1-2% Mg, revealed the coexistence of paramagnetic (PM) and antiferromagnetic (AFM) resonance modes below the Néel point. The ordering is known to be due to the restoring of the AFM staggered magnetization near impurities. The surprising PM spectral component indicates a nonuniform phase: clusters of staggered magnetization, touching each other, form AFM areas, though some clusters are isolated from AFM areas by the residual of the spin-gap matrix. Isolated clusters provide PM signals due to their net spin.
Coexistence of Gap-less and Gapped Excitations in NH4CuCl3
Hiroyuki Nojiria, Hidekazu Tanakab, Buddy Kurniawanc, Mitsuhiro Motokawad
aDepartment of Physics, Okayama University, Tsushimanaka 3-1-1, Okayama 700-8530, Japan
bDepartment of Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan
cDepartment of Physics, University of Indonesia, Depok 16424, Indonesia
dInstitute for Material Research, Tohoku University, Sendai 980-8577, Japan
ESR investigations are performed on a low dimensional compound NH4CuCl3 with magnetization plateaux. In the phase below the [ 1/4]-plateau, a coexistence of two-types of triplets and a gap-less mode is found. Below 1.3 K at which spins of the gap-less mode show some magnetic ordering, the higher energy triplet mode exhibit no changes. In addition to the previously reported gapped modes at [ 1/4]- and [ 3/4]-plateaux, a new low energy mode is found at the half of the saturation field. This mode may be related to an ïrrelevant instability" of [ 1/2]-plateau that has not been found in the previous static magnetization measurement.
Low temperature NMR studies of Na2V3O7
J. L. Gavilanoa, D. Raua, Sh. Mushkolaja, H. R. Otta, F. Milab, P. Milletc
aLaboratorium für Festkörperphysik, ETH-Hönggerberg, CH-8093 Zürich, Switzerland
bInstitut de Physique Théorique, Université de Lausanne, CH - 1015 Lausanne, Switzerland
cCentre d'Elaboration des Matériaux et d'Etudes Structurales, 31055 Toulouse Cedex, France
We have performed 23Na-NMR measurements on the quasi one-dimensional spin 1/2 system Na2V3O7 at low temperatures. The temperature dependence of the spin lattice relaxation rate T1-1(T) measured at 78 MHz exhibits a narrow peak near 2.5 K, indicating the onset of a cooperative phase transition to a state with a small gap in the spectrum of V spin excitations. Considering the results of the susceptibility at higher temperatures, it seems likely that this transition reflects the onset of antiferromagnetic order. The observed increase of the critical temperature, upon enhancing the applied magnetic field, however, indicates that the nature of the transition must be investigated in more detail.
Single-component Ferrimagnetism by an Organic Triradical and Variable Spin-network Composed of Organic Polyradicals
Yuko Hosokoshi, Keiichi Katoh, Katsuya Inoue
Institute for Molecular Science; School of Mathematical and Physical Science, The Graduate University for Advanced Studies, Nishigonaka 38, Okazaki, Aichi 444-8585, Japan
Focusing on the quantum nature of organic radicals which consist only of light elements, we have constructed several spin networks. Intramolecular magnetic exchange couplings are controllable by the design of the molecular structure. An organic biradical BNO [BNO=1,3-bis(N-tert-butylaminoxyl)benzene] can be regarded as an S=1 species, since BNO consists of S=1/2 spin pairs (dimers) in which the two spins are coupled ferromagnetically with 2J/kB ³ 600 K. Combination of the BNO unit and another S=1/2 species by the intra- and intermolecular antiferromagnetic interactions results in the ferrimagnetic network. Properties of the ferrimagnetic PNNBNO molecule and related materials are presented.