Spin susceptibility and low-lying excitations in the Haldane-gap compound Y2BaNiO5

Structural and magnetic properties of spin-1/2 dimer compound Cu2(IPA)2(DMF)(H2O) with a large spin gap

We present the synthesis and a detailed investigation of structural and magnetic properties of metal-organic compound Cu₂(IPA)₂(DMF)(H₂O) by means of x-ray diffraction, magnetization, and heat capacity measurements. Single crystals of the title compound were synthesized by judicious selection of organic ligand and employing a selective hydrothermal reaction route. It crystallizes in an orthorhombic structure with space group Cmca. The structural analysis revealed that two Cu²⁺ ions are held together by the organic component (-O-C-O-) in a square paddle-wheel to form spin dimers which are aligned perpendicular to each other and are further coupled through organic ligands (isophthalic acid) forming two-dimensional layers. Temperature dependent magnetic susceptibility [Formula: see text] could be described well using spin-1/2 dimer model. The spin susceptibility [Formula: see text] shows an exponential decrease in the low temperature region, below the broad maximum, confirming the singlet ground state with a large spin gap of [Formula: see text] K. The heat capacity C _p measured as a function of temperature also confirms the absence of magnetic long-range-order down to 2 K.

Successive spin orderings of tungstate-bridged Li2Ni(WO4)2 of spin 1

Magnetic, thermodynamic, and dielectric properties of Li2Ni(WO4)2 of S  =  1 system have been studied using magnetic susceptibility, specific heat, and dielectric constant measurements. The magnetic orderings can be identified in three stages, including a short range magnetic ordering indicated by the rounded χ(T) peak with maximum at  ∼20 K, and signatures of two successful antiferromagnetic long range orderings near T(N1) ~ 18 K and T(N2) ~ 13 K revealed by the d(χ(T)) /d(T) peaks. The successive long range magnetic orderings are related to the quasi triangular symmetry breaking in the ac- and bc-planes and to the change of the dielectric constant, suggesting the presence of spin-phonon coupling. The specific heat and magnetic entropy analysis for Li2Ni(WO4)2 shows the existence of a significant low dimensional magnetic correlations at high temperature and confirms the long range three-dimensional (3D) behavior of magnetic orderings below T(N1) and T(N2).