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Register a new userElectronic structure of KTi(SO4)2.H2O - a S=1/2 frustrated chain antiferromagnet
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The compound KTi(SO4)2.H2O was recently reported as a quasi one-dimensional spin 1/2 compound with competing antiferromagnetic nearest neighbor exchange J1 and next-nearest neighbor exchange J2 along the chain with a frustration ratio alpha = J2/J1 ~ 0.29 [Chem. Mater. vol. 20, pg. 8 (2008)]. Here, we report a microscopically based magnetic model for this compound derived from density functional electronic structure calculations along with respective tight-binding models. Our calculations confirm the quasi one-dimensional nature of the system with antiferromagnetic J1 and J2, but suggest a significantly larger frustration ratio alpha ~ 1.1 +- 0.2. Based on transfer matrix renormalization group calculations we found that, due to an intrinsic symmetry of the J1-J2 model, our larger frustration ratio alpha is also consistent with the previous thermodynamic data. To resolve this issue, we propose performing high-field magnetization measurements and low temperature susceptibility measurements which should allow to precisely identify the frustration ratio alpha.
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From experimental and theoretical analyses of magnetic and specific-heat properties, we present the complete magnetic phase diagram of the quasi-one-dimensional antiferromagnet Cu(N$_2$H$_5$)$_2$(SO$_4$)$_2$. On cooling and at zero magnetic field this compound enters a one-dimensional regime with short-range magnetic correlations, marked by a broad maximum in the specific heat and magnetic susceptibility at $T_mathrm{max}sim 2,mathrm{K}$, followed by an ordered antiferromagnetic phase below $T_mathrm{N}sim 1,mathrm{K}$ induced by small interchain couplings. The intermediate-temperate one-dimensional regime can be modeled using exact quantum-transfer-matrix calculations, which perfectly describe the nonmonotonic behavior of T_max as a function of the magnetic field, giving $J = 4.25,mathrm{K}$ for the intrachain exchange parameter. The analysis of magnetic specific-heat and susceptibility data at low temperature indicates that the interchain exchange couplings are an order of magnitude smaller than the coupling inside the chains.
We present the results of magnetization, ESR and NMR measurements on single crystal samples of the frustrated S=1/2 chain cuprate LiCu2O2 doped with nonmagnetic Zn^2+. As shown by the x-ray techniques the crystals of Li(Cu{1-x}Zn{x})2O2 with x<0.12 are single-phase, whereas for higher Zn concentrations the samples were polyphase. ESR spectra for all monophase samples (0<= x<0.12) can be explained within the model of a planar spin structure with a uniaxial type anisotropy. The NMR spectra of the highly doped single crystal sample Li(Cu0.9Zn0.1)2O2 can be described in the frame of a planar spin glass like magnetic structure with short range spiral correlations in the crystal (ab)-planes with strongest exchange bonds. The value of magnetic moments of Cu^2+ ions in this structure is close to value obtained for undoped crystals: (0.8 +- 0.1) mu_B.
We present the results of the magnetization and dielectric constant measurements on untwinned single crystal samples of the frustrated S=1/2 chain cuprate LiCu_2O_2. Novel magnetic phase transitions were observed. A spin flop transition of the spiral spin plane was observed for the field orientations H||a,b. The second magnetic transition was observed at H~15 T for all three principal field directions. This high field magnetic phase is discussed as a collinear spin-modulated phase which is expected for an S=1/2 nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic chain system.
We have studied the structural, magnetic properties, and electronic structure of the compound InCuPO5 synthesized by solid state reaction method. The structure of InCuPO5 comprises of S = 1/2 uniform spin chains formed by corner-shared CuO4 units. Magnetic susceptibility chi(T) data shows a broad maximum at about 65 K, a characteristic feature of one-dimensional (1D) magnetism. The chi(T) data is fitted to the coupled, S = 1/2 Heisenberg antiferromagnetic (HAFM) uniform chain model that gives the intra-chain coupling (J/kB) between nearest neighbour Cu2+ ions as -100 K and the ratio of inter-chain to intra-chain coupling (J/J) as about 0.07. The exchange couplings estimated from the magnetic data analysis are in good agreement with the computed values from the electronic structure calculations based on density functional theory + Hubbard U (DFT+U) approach. The combination of theoretical and experimental analysis confirms that InCuPO5 is a candidate material for weakly coupled S = 1/2 uniform chains. A detailed theoretical analysis of the electronic structure further reveals that the system is insulating with a gap of 2.4 eV and a local moment of 0.70 muB /Cu.
The field induced magnetic phase transitions of Cs$_2$CuBr$_4$ were investigated by means of magnetization process and neutron scattering experiments. This system undergoes magnetic phase transition at Ne{e}l temperature $T_mathrm{N}=1.4$ K at zero field, and exhibits the magnetization plateau at approximately one third of the saturation magnetization for the field directions $Hparallel b$ and $Hparallel c$. In the present study, additional symptom of the two-third magnetization plateau was found in the field derivative of the magnetization process. The magnetic structure was found to be incommensurate with the ordering vector $boldsymbol{Q}=(0, 0.575, 0)$ at zero field. With increasing magnetic field parallel to the c-axis, the ordering vector increases continuously and is locked at $boldsymbol{Q}=(0, 0.662, 0)$ in the plateau field range $13.1 mathrm{T} < H < 14.4 mathrm{T}$. This indicates that the collinear textit{up-up-down} spin structure is stabilized by quantum fluctuation at the magnetization plateau.
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