21 research outputs found
Spangolite: an s=1/2 maple leaf lattice antiferromagnet?
Spangolite, Cu6Al(SO4)(OH)12Cl.3H2O, is a hydrated layered copper sulphate
mineral. The Cu2+ ions of each layer form a systematically depleted triangular
lattice which approximates a maple leaf lattice. We present details of the
crystal structure, which suggest that in spangolite this lattice actually
comprises two species of edge linked trimers with different exchange
parameters. However, magnetic susceptibility measurements show that despite the
structural trimers, the magnetic properties are dominated by dimerization. The
high temperature magnetic moment is strongly reduced below that expected for
the six s=1/2 in the unit cell.Comment: Accepted for JPCM Frustrated Magnetism special issue, added reference
[5] in replacemen
Dispersive excitations in the high-temperature superconductor La2-xSrxCuO4
High-resolution neutron scattering experiments on optimally doped La2-xSrxCuO4 (x=0.16) reveal that the magnetic excitations are dispersive. The dispersion is the same as in YBa2Cu3O6.85, and is quantitatively related to that observed with charge sensitive probes. The associated velocity in La2-xSrxCuO4 is only weakly dependent on doping with a value close to the spin-wave velocity of the insulating (x=0) parent compound. In contrast with the insulator, the excitations broaden rapidly with increasing energy, forming a continuum at higher energy and bear a remarkable resemblance to multiparticle excitations observed in 1D S=1/2 antiferromagnets. The magnetic correlations are 2D, and so rule out the simplest scenarios where the copper oxide planes are subdivided into weakly interacting 1D magnets
Multiple magnon modes and consequences for the Bose-Einstein condensed phase in BaCuSi2O6
The compound BaCuSi2O6 is a quantum magnet with antiferromagnetic dimers of S=1/2 moments on a quasi-2D square lattice. We have investigated its spin dynamics by inelastic neutron scattering experiments on single crystals with an energy resolution considerably higher than in an earlier study. We observe multiple magnon modes, indicating clearly the presence of magnetically inequivalent dimer sites. The more complex spin Hamiltonian revealed in our study leads to a distinct form of magnon Bose-Einstein condensate phase with a spatially modulated condensate amplitude
Origin of the Spin-Orbital Liquid State in a Nearly J=0 Iridate Ba3ZnIr2O9
We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba3ZnIr2O9 is a realization of a novel spin-orbital liquid state. Our results reveal that Ba3ZnIr2O9 with Ir5+ (5d(4)) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J = 0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir2O9 dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK
Micro-fabrication process for small transport devices of layered manganite
Devices have been fabricated based on the bilayer manganite La(1.4)Sr(1.6)Mn(2)O(7), which in the bulk state orders magnetically below 90 K, at which point both in-plane and c-axis bulk resistivity decrease by 2-3 orders of magnitude. We provide an optimized procedure to fabricate devices to electrical transport in-and out of plane. Fabricated mesoscopic devices have dimensions comparable to a typical magnetic domain, allowing us to study structures going from a single domain to several domains. © 2012, American Institute of Physics
Direct electric field control of the skyrmion phase in a magnetoelectric insulator
Magnetic skyrmions are topologically protected spin-whirls currently considered as promising for use in ultra-dense memory devices. Towards achieving this goal, exploration of the skyrmion phase response and under external stimuli is urgently required. Here we show experimentally, and explain theoretically, that in the magnetoelectric insulator Cu2OSeO3 the skyrmion phase can expand and shrink significantly depending on the polarity of a moderate applied electric field (few V/ÎŒm). The theory we develop incorporates fluctuations around the mean-field that clarifies precisely how the electric field provides direct control over the free energy difference between the skyrmion and the surrounding conical phase. The quantitative agreement between theory and experiment provides a solid foundation for the development of skyrmionic applications based on magnetoelectric coupling
Quantum phase transition of a magnet in a spin bath
The excitation spectrum of a model magnetic system, LiHoF, has been
studied using neutron spectroscopy as the system is tuned to its quantum
critical point by an applied magnetic field. The electronic mode softening
expected for a quantum phase transition is forestalled by hyperfine coupling to
the nuclear spins. We show that interactions with the nuclear spin bath control
the length scale over which the excitations can be entangled. This generic
result limits how far it is possible to approach intrinsic electronic quantum
criticality.Comment: 13 pages, 3 figures, pre-proof versio