Weak antiferromagnetism due to Dzyaloshinskii-Moriya interaction in Ba 3 Cu 2 O 4 Cl 2 (original) (raw)
Related papers
Physical Review B, 2006
Ba 2 Cu 3 O 4 Cl 2 has two inter-penetrating square Cu sublattices, one with square root 2 times the in-plane spacing of the other. Isotropic magnetic interactions between the two sublattices are completely frustrated. Quantum fluctuations resolve the intrinsic degeneracy in the ordering direction of the more weakly coupled sublattice in favor of collinear ordering. We present neutron scattering and magnetization studies of the magnetic structure when the Cu ions are substituted with Co. The Co spins create new magnetic interactions between the two sublattices. The ordering behavior of both Cu sublattices is retained largely unmodified. Between the phase transitions of the two sublattices spin-glass behavior is observed. Magnetization results show a strong enhancement to the ferromagnetic aspect of the magnetic structure. The combination of glassy behavior and large moments strongly suggest that the Co moments induce the formation of local canted states.
Spin-wave dispersion and transition temperature in the cuprate antiferromagnetLa2CuO4
Physical Review B, 2003
We have studied the spin-wave dispersion at low temperatures and the transition temperature (T N) of the spin-1 2 antiferromagnet and high-T C parent La 2 CuO 4. The values of the in-plane exchange parameters ͑including first, second, and third nearest neighbors͒ are determined by an accurate fit to the recently experimentally observed in-plane spin-wave spectrum, obtained by the high-resolution inelastic neutron scattering performed on La 2 CuO 4 ͓Phys. Rev. Lett. 86, 5377 ͑2001͔͒. The analysis of the Néel temperature shows that the in-plane spin anisotropy () is much more significant than the three dimensionality, since T N of the three-dimensional ͑3D͒-antiferromagnet depends rather weakly on the value of the interlayer coupling (Ќ). We obtain that the Néel temperature of the 3D-antiferromagnet varies only weakly within the very wide interval of Ќ and the Néel temperature of the anisotropic 2D (0, Ќ ϭ0) antiferromagnet does not differ from the 3D value for the same. These conclusions are valid for both tetragonal and orthorhombic structures. However, dependence of T N is essentially different: for ϭ0, T N of the tetragonal structure becomes 0, while T N of the orthorhombic structure remains finite. These results are valid within the frame of the Tyablikov approximation.
Effects of cyclic four-spin exchange on the magnetic properties of the CuO2 plane
Physical review. B, Condensed matter, 1993
For the Cu02 square lattice, as a parent system of high-T, superconductors, a numerical study has suggested that the effective-spin model contains a large cyclic four-spin exchange interaction J,. This paper investigates the effects of J, upon magnetic Raman scattering and upon properties of the ground state by an exact numerical method mainly for a 16-site cluster. It is found that the main Raman peak with the Bzg symmetry is shifted by 20% to the lower-energy side with a realistic magnitude for J"which is about one fourth the size of the nearest-neighbor exchange J. Accordingly a value of J extracted from analyses of experimental data becomes larger by 10% than that estimated with the use of the Heisenberg model. Furthermore the four-spin exchange enhances a shoulder due to multimagnon states at an energy of about 4J, and this result compares favorably with the experimental line shape. Detailed discussion is given on the effect of the four-spin exchange upon the ground-state properties such as the staggered magnetization, the ground-state energy, weight of various spin configurations, and the spin-spin correlation function.
Journal of Physics: Condensed Matter, 2013
The title compounds have dominant ferromagnetic (FM) exchange interactions within one-dimensional (1D) half-twist ladders of s = ½ Cu 2+ ions and antiferromagnetic (AFM) interactions between ladders, leading to ordered 3D phases at temperatures below 20K. Here we show that a microscopic 1D model of the paramagnetic (PM) phase combined with a phenomenological model based on sublattice magnetization describes the observed temperature and field dependent magnetism. The model identifies AFM, spin-flop (SF) and PM phases whose boundaries have sharp features in the experimental magnetization M(T,H) and specific heat C P (T,H). Exact diagonalization (ED) of the 1D model, possible for 24 spins due to special structural features of half-twist ladders, yields the magnetization and spin susceptibility of the PM phase. AFM interactions between
Physical Review B, 2009
Spin-only descriptions of the half-filled one-band Hubbard model are relevant for a wide range of Mott insulators. In addition to the usual Heisenberg exchange, many new types of interactions, including ring exchange, appear in the effective Hamiltonian in the intermediate coupling regime. In order to improve on the quantitative description of magnetic excitations in the insulating antiferromagnetic phase of copper-oxide (cuprate) materials, and to be consistent with band structure calculations and photoemission experiments on these systems, we include second and third neighbor hopping parameters, t ′ and t ′′ , into the Hubbard Hamiltonian. A unitary transformation method is used to find systematically the effective Hamiltonian and any operator in the spin-only representation. The results include all closed, four hop electronic pathways in the canonical transformation. The method generates many ring exchange terms that play an important role in the comparison with experiments on La2CuO4. Performing a spin wave analysis, we calculate the magnon dispersion as a function of U, t, t ′ and t ′′. The four parameters are estimated by fitting the magnon dispersion to the experimental results of Coldea et al. [Phys. Rev. Lett. 86, 5377, 2001] for La2CuO4. The ring exchange terms are found essential, in particular to determine the relative sign of t' and t ′′ , with the values found in good agreement with independent theoretical and experimental estimates for other members of the cuprate family. The zero temperature sublattice magnetization is calculated using these parameters and also found to be in good agreement with the experimental value estimated by Lee et al. [Phys. Rev. B 60, 3643 (1999)]. We find a value of the interaction strength U ≃ 8t consistent with Mott insulating behavior.
Novel spin lattice in Cu 3 TeO 6 : an antiferromagnetic order and domain dynamics
Journal of Physics: Condensed Matter, 2005
We report on magnetic properties of cubic compound Cu3TeO6 studied by ac and dc susceptibility and neutron powder diffraction for the first time. A novel magnetic lattice, three dimensional spin web, composed of almost planar regular hexagons of Cu 2+ 1/2 spins, defines the properties of Cu3TeO6. The behaviour of the magnetic susceptibility in the paramagnetic state at ≈ 170 K is suggestive for a competition between local anisotropies of Cu 2+ hexagons. The resulting frustration is weaker than the antiferromagnetic nearest-neighbor interaction which leads to a collinear (or slightly canted) spin arrangement (k=0,0,0) and formation of magnetic domains below TN = 61 K.
Weak magnetism in insulating and superconducting cuprates
Physical Review B, 2010
X-ray magnetic circular dichroism provides evidence of an out-of-plane spin moment in undoped and doped cuprates. In La 2 CuO 4 this moment is related to the canting of the antiferromagnetically ordered Cu 2+ spins caused by the Dzyaloshinskii-Moriya interaction within the CuO 2 planes. This canting gives rise to the wellknown weak ferromagnetism in high magnetic fields. We find a similar behavior in doped compounds, both in the normal and in the superconducting state, but with a different temperature dependence typical of paramagnetic systems. This result suggests that, together with short-range in-plane antiferromagnetic correlations, the Dzyaloshinskii-Moriya interaction survives up to optimal doping and in the superconducting state.
Magnetic ordering in the frustrated Heisenberg chain system cupric chloride CuCl2
Physical Review B, 2009
We report a detailed examination the magnetic structure of anhydrous cupric chloride CuCl 2 carried out by powder neutron diffraction, magnetic susceptibility and specific heat measurements on polycrystalline and single crystal samples as well as an evaluation of the spin exchange interactions by first principles density functional theory (DFT) calculations. Anhydrous CuCl 2 shows one dimensional antiferromagnetic behavior and long range antiferromagnetic ordering below a Néel temperature of 23.9 K. Neutron powder and single crystal diffraction reveal that, below 23.9 K, CuCl 2 undergoes a phase transition into an incommensurate magnetic structure (propagation vector (1,0.2257,0.5) with a spin-spiral propagating along b and the moments confined in the bc crystallographic plane. Our DFT calculations show that the spin-spiral results from competing ferromagnetic nearest neighbor and antiferromagnetic next-nearest neighbor spin-exchange interaction along the spin chains. Implications for possible multiferroic behavior of CuCl 2 are discussed.
Physical Review B, 2009
In Cu 2 CdB 2 O 6 , a quantum-mechanical 1/2 magnetization plateau and classical antiferromagnetic long-range order ͑AF-LRO͒ appear. Two crystallographic Cu sites ͑Cu1 and Cu2͒ exist and have spin-1/2. It was speculated previously that spins on the Cu1 sites were in a nearly singlet state and that spins on the Cu2 sites formed the long-range order in weak magnetic fields and were almost saturated in fields of the magnetization plateau. As described herein, we report the magnetic structure of Cu 2 114 Cd 11 B 2 O 6 as determined using neutron powderdiffraction measurements. Contrary to that previous speculation, both the Cu1 and Cu2 spins have large magnetic moments in the ordered state. We discuss the mechanism which causes the magnetization plateau and AF-LRO.