arXiv subjects

I. A. Zaliznyak

Publications and source records attributed to I. A. Zaliznyak.

50 records · Page 3Linked to original sources

arXiv2007

Stripeless incommensurate magnetism in a doped strongly correlated oxide

We studied the nano-scale structure of the short-range incommensurate magnetic order in La1.5Sr0.5CoO4 by elastic neutron scattering. We find that magnetic diffuse scattering is isotropic in the a-b plane, in contrast with the naive expectation based on the popular stripe model. Indeed, charge segregation into lines favoring certain lattice direction(s) would facilitate linear stacking faults in an otherwise robust antiferromagnetism of un-doped material, leading to anisotropic disorder, with a characteristic symmetry pattern present in the neutron scattering data.

cond-mat.str-el↗

arXiv2004

Universal features of charge and spin order in a half-doped layered perovskite

We have investigated the peculiar structure of charge and spin ordering in the half-doped layered perovskite oxide La$_{1.5}$Sr$_{0.5}$CoO$_4$ by elastic neutron scattering. Two samples with different preparation histories were studied. We find that the generic features of the ordered states, such as their short-range, glassy nature and the spin incommensurability, are sample-independent. At the same time, some subtle features of the ordered phases, such as the correlation lengths, differ.

cond-mat.str-el↗

arXiv2003

Spinons in the strongly correlated copper oxide chains in SrCuO2

We have investigated the spin dynamics in the strongly correlated chain copper oxide SrCuO$_2$ for energies up to $\gtrsim 0.6$ eV using inelastic neutron scattering. We observe an acoustic band of magnetic excitations which is well described by the "Muller-ansatz" for the two-spinon continuum in the S=1/2 antiferromagnetic Heisenberg spin chain. The lower boundary of the continuum extends up to $\approx 360$ meV, which corresponds to an exchange constant $J = 226(12)$ meV. Our finding that an effective Heisenberg spin Hamlitonian adequately describes the spin sector of this 1D electron system, even though its energy scale is comparable to that of charge excitations, provides compelling experimental evidence for spin-charge separation.

cond-mat.str-el↗

arXiv2003

Spiral order induced by distortion in frustrated square-lattice antiferromagnet

In a strongly frustrated square-lattice antiferromagnet with diagonal coupling J', for J/(2J') < 1, an incommensurate spiral state with propagation vector Q = (π+/- δ, π+/- δ) near (π,π) competes closely with the Neel collinear antiferromagnetic ground state. For classical Heisenberg spins the energy of the spiral state can be lowered as it adapts to the distortion of the crystal lattice. As a result, a weak superstructural modulation such as exist in doped cuprates might stabilize an incommensurate spiral phase for some range of the parameter J/(2J') close to 1.

cond-mat.str-el↗

arXiv2003

Modification of the classical Heisenberg helimagnet by weak uniaxial anisotropy and magnetic field

Classical ground state of the isotropic Heisenberg spin Hamiltonian on a primitive Bravais lattice is known to be a single-Q planar spin spiral. A uniaxial anisotropy and external magnetic field distort this structure by generating the higher-order Fourier harmonics at wave-vectors nQ in the spatial spin configuration. These features are not captured in the formalism based on the Luttinger-Tisza theorem, where the classical ground state energy is minimized under the ``weak'' condition on the length of the spins. We discuss why the correct solution is lost in that approach and present an alternative microscopic treatment of the problem. It allows to find the classical ground state for general Q for both easy-axis and easy-plane uniaxial second-order anisotropy, and for any orientation of the magnetic field, by treating the effect of anisotropy (but not the field) as a perturbation to the exchange structure. As a result, the classical ground state energy, the uniform magnetization, and the magnetic Bragg peak intensities that are measured in experiment, are calculated.

cond-mat.str-el↗

arXiv2003

Continuum in the spin excitation spectrum of a Haldane chain (erratum)

There was a slight error in calculating the nonlinear sigma-model prediction for the 2-magnon scattering continuum shown in Fig. 2 of cond-mat/0010049, and Phys. Rev. Lett. {\bf 87}, 017202 (2001). Present erratum explains what was incorrect, and shows a corrected version of the figure. The correction is minor and does not affect main conclusions drawn in the original paper.

cond-mat.str-el↗

arXiv2002

Structure of end states for a Haldane Spin Chain

Inelastic neutron scattering was used to probe edge states in a quantum spin liquid. The experiment was performed on finite length antiferromagnetic spin-1 chains in Y_2BaNi_{1-x}Mg_xO_5. At finite fields, there is a Zeeman resonance below the Haldane gap. The wave vector dependence of its intensity provides direct evidence for staggered magnetization at chain ends, which decays exponentially towards the bulk (xi = 8(1) at T=0.1K). Continuum contributions to the chain end spectrum indicate inter-chain-segment interactions. We also observe a finite size blue shift of the Haldane gap.

cond-mat.str-el↗

arXiv2001

Continuum spin excitations in S=1 one-dimensional antiferromagnet

We present detailed measurement of the non-hydrodynamic part of the spin excitation spectrum in the model quasi-1D S=1 antiferromagnet CsNiCl3 by inelastic magnetic neutron scattering. In the better part of the Brillouin zone the effect of the inter-chain coupling is negligible, and spin dynamics reflects that of a single Haldane chain. We find that at q ~< 0.6pi this quantum spin system ceases to support coherent propagating excitation, which gradually turns into a continuum band of states, whose width grows with decreasing q. This finding is consistently verified under different resolution conditions, obtained with two different high-luminosity experimental setups.

cond-mat.str-el↗

arXiv2001

Spin-entropy driven melting of the charge order in La1.5Sr0.5CoO4

We studied the melting of the charge order in the half-doped tetragonal perovskite La1.5Sr0.5CoO4 by elastic neutron scattering. We found that diffuse peaks, corresponding to the breathing-type modulation of oxygen positions in the CoO6 octahedra, disappear above Tc = 825(27) K. This melting of the diffuse superstructure is reversible (no change in the correlation lengths upon annealing is observed) and accompanied by a large nonlinear thermal expansion along the tetragonal c-axis, with a cusp at Tc. We conclude that quenched disorder of the doped Sr ions is at the origin of this anisotropic charge glass state. We also suggest that its melting is driven by the transition from the intermediate- to the high-spin state of Co{3+} ion, which is favored by the spin entropy at high T.

cond-mat.str-el↗

arXiv2000

Continuum in the spin excitation spectrum of a Haldane chain, observed by neutron scattering in CsNiCl3

The spin excitation continuum, expected to dominate the low-energy fluctuation spectrum in the Haldane spin chain around the Brillouin zone center, q=0, is directly observed by inelastic magnetic neutron scattering in the S=1 quasi-1D antiferromagnet CsNiCl3. We find that the single mode approximation fails, and that a finite energy width appears in the dynamic correlation function S(q,omega) for q < 0.5pi. The width increases with decreasing q, while S(q,omega) acquires an asymmetric shape qualitatively similar to that predicted for the 2-magnon continuum in the nonlinear sigma-model.

cond-mat.str-el↗

arXiv2000

Independent freezing of charge and spin dynamics in La1.5Sr0.5CoO4

We present elastic and quasielastic neutron scattering measurements characterizing peculiar short-range charge-orbital and spin order in the layered perovskite material La1.5Sr0.5CoO4. We find that below Tc~750 K holes introduced by Sr doping lose mobility and enter a statically ordered {\it charge glass} phase with loosely correlated checkerboard arrangement of empty and occupied d{3z2-r2} orbitals (Co3+ and Co2+). The dynamics of the resultant mixed spin system is governed by the anisotropic nature of the crystal-field Hamiltonian and the peculiar exchange pattern produced by the orbital order. It undergoes a {\it spin freezing} transition at much a lower temperature, Ts~30 K.

cond-mat.str-el↗

arXiv1999

Anisotropic spin freezing in the S=1/2 zigzag ladder compound SrCuO2

Using magnetic neutron scattering we characterize an unusual low temperature phase in orthorhombic SrCuO2. The material contains zigzag spin ladders formed by pairs of S=1/2 chains (J=180 meV) coupled through a weak frustrated interaction |J'|<0.1J. At T<Tc1=5.0(4)K an elastic peak develops in a gapless magnetic excitation spectrum indicating spin freezing on a time scale larger than 200 picoseconds. While the frozen state has long range commensurate antiferromagnetic order along the chains with the correlation length exceeding 200 lattice periods along the c-axis and a substantial correlation length of 60(25) spacings along the a-axis perpendicular to the zigzag plane, only 2 lattice units are correlated along the b-axis which is the direction of the frustrated interactions. The frozen magnetic moment of each Cu ion is very small, 0.033(7) Bohr magneton even at T=0.35K, and has unusual temperature dependence with a cusp at Tc2=1.5K reminiscent of a phase transition. We argue that slow dynamics of stripe-like cooperative magnetic defects in tetragonal a-c planes yield this anisotropic frozen state.

cond-mat.mtrl-sci↗

arXiv1997

Tuning the spin Hamiltonian of NENP by external pressure: a neutron scattering study

We report an inelastic neutron scattering study of antiferromagnetic spin dynamics in the Haldane chain compound Ni(C2H8N2)2NO2ClO4 (NENP) under external hydrostatic pressure P = 2.5 GPa. At ambient pressure, the magnetic excitations in NENP are dominated by a long-lived triplet mode with a gap which is split by orthorhombic crystalline anisotropy into a lower doublet centered at $Δ_\perp\approx$ 1.2meV and a singlet at $Δ_\parallel\approx$ 2.5meV. With pressure we observe appreciable shifts in these levels, which move to $Δ_\perp{(2.5GPa)}\approx$ 1.45 meV and $Δ_\parallel(2.5GPa)\approx$ 2.2meV. The dispersion of these modes in the crystalline c-direction perpendicular to the chain was measured here for the first time, and can be accounted for by an interchain exchange J'_c approximately 3e-4*J which changes only slightly with pressure. Since the average gap value $Δ_H\approx$ 1.64 meV remains almost unchanged with P, we conclude that in NENP the application of external pressure does not affect the intrachain coupling J appreciably, but does produce a significant decrease of the single-ion anisotropy constant from D/J = 0.16(2) at ambient pressure to D/J = 0.09(7) at P = 2.5 GPa.

cond-mat↗

arXiv1995

Static properties of a quasi one-dimensional antiferromagnet in magnetic field

We calculate the effect of zero-point fluctuations on the magnetostatic properties of a quasi one-dimensional antiferromagnetic helimagnet with and without in-plane anisotropy. We find substantial reduction of the uniform susceptibility and the sublattice magnetization from their classical values and appreciable renormalization of the spin-flop field at $T=0$. The magnetization curve varies nonlinearly at small fields and is described by a universal formula at high fields. The results are compared with numerical simulations on one-dimensional systems and measurements in the CsNiCl$_3$-type compounds.

cond-mat↗