Two-dimensionalS=12Heisenberg antiferromagnets: Synthesis, structure, and magnetic properties

Abstract

The magnetic susceptibility and magnetization of two new layered S= 1 2Heisenberg antiferromagnets with moderate exchange are reported.The two isostructural compounds, (2-amino-5-chloropyridinium)2CuBr4 ((5CAP)2CuBr4) and (2-amino-5-methylpyridinium)2CuBr4 ((5MAP)2CuBr4), contain S= , Cu(II) ions related by C-centering, yielding four equivalent nearest neighbors. The crystal structure of newly synthesized compound, (5CAP)2CuBr4, shows the existence of layers of distorted copper(II)-bromide tetrahedra parallel to the ab plane, separated by the organic cations along the c axis. Magnetic pathways are available through the bromide-bromide contacts within the layers and provide for moderate antiferromagnetic exchange. Susceptibility measurements indicate interaction strengths to be 8.5(1) K, and 6.5(1) K and ordering temperatures of 5.1(2) K and 3.8(2) K for (5CAP)2CuBr4 and (5MAP)2CuBr4 respectively. High field magnetization experiments on both compounds show upward curvature of M(H,T). Magnetization measurements made at T = 1.3 K show saturation occurs in (5MAP)2CuBr4 at 18.8 T and in (5CAP)2CuBr4 at 24.1 T. The magnetization curves are consistent with recent theoretical predictions. Single crystal magnetization measured at 2.0 K indicate a spin flop transition at 0.38 T and 0.63 T for (5CAP)2CuBr4 and (5MAP)2CuBr4 respectively.

Tuning the magneto-structural properties of non-porous coordination polymers by HCl chemisorption

“…The most plausible exchange pathway in 2 involves a two-halide Cu-Cl···Cl-Cu interaction (Fig. 5a) 36,37 , although it may also contain some influence from other potential superexchange mechanisms, such as Cu-Cl···Cu interactions or N-H···Cl-Cu hydrogen bonds. Because of the rapid release of HCl by 2 (conversion to 3), magnetic measurements were performed under HCl atmosphere to guarantee homogeneity during the magnetic measurements.…”

An extremely well isolated 2D-antiferromagnetic layer

“…4). Based upon the connectivity of the Cu(II) ions via pyrazine molecules, the data was initially fit to the uniform antiferromagnetic 2D-Heisenberg model [12] where C = the Curie Constant, J = magnetic exchange constant and p = percent paramagnetic impurity. As can be seen in Fig.…”

CuCl2(C10H8N2) - S=1/2 Heisenberg Antiferromagnet on Square Lattice

“…2). For the comparison of experimental magnetization with numerical predictions [9] of 1d and 2d QHAF the saturation magnetization and field have been estimated using T = 0 K mean-field approximation [8] with exchange couplings obtained from susceptibility data. The discrepancies (see Fig.…”

“…Magnetization of CuCl2(bipy) measured at 5 and 10 K compared to the numerical prediction for 1d (solid line) and 2d (dotted line) QHAF[9].…”