Magnetic studies of the two-dimensional, S=1/2 Heisenberg antiferromagnets (5CAP)2CuCl4 and (5MAP)2CuCl4

Abstract

The magnetic materials ͑5CAP͒ 2 CuCl 4 and ͑5MAP͒ 2 CuCl 4 form effective square planar lattices of CuCl 4 2Ϫ anions. The Cu 2ϩ ions have weak antiferromagnetic interactions in the plane through Cl-Cl contacts. These planes are well separated by the 5MAP and 5CAP organic groups. High temperature susceptibility measurements give Jϭ0.57 K for ͑5CAP͒ 2 CuCl 4 and Jϭ0.38 K for ͑5MAP͒ 2 CuCl 4 . (T,Hϭ0) for these materials has a rounded maximum at T peak ϭ1.1 K for ͑5CAP͒ 2 CuCl 4 and T peak ϭ0.62 K for ͑5MAP͒ 2 CuCl 4 . A kink in (T,Hϭ0) for the ͑5MAP͒ 2 CuCl 4 suggests a phase transition to three-dimensional long range order at T C ϭ0.44 K. Measurements of (T,H) show that the saturation field H C for the transition to a fieldinduced saturated state is 3.78 T for ͑5CAP͒ 2 CuCl 4 and 2.17 T for ͑5MAP͒ 2 CuCl 4 . Thus these materials are excellent model systems in which to explore the full H -T phase diagram of the two-dimensional Sϭ1/2 Heisenberg antiferromagnet.

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

“…The T = 0 K magnetization curve is predicted to have a weak logarithmic divergence at H sat due to the quenching of quantum fluctuations 5 , but this feature is not observed because the high field magnetization curve is rounded due to the presence of thermal excitations. The magnetization curve M(H,T) has recently been calculated for several finite temperatures by Quantum MonteCarlo techniques 20 ; these results are presented in Figure 6 Similar magnetization behavior has been observed experimentally 16 for the analogous chloride complexes, (5CAP) 2 CuCl 4 and (5MAP) 2 CuCl 4 . The isostructural chloride compounds have significantly weaker exchange interactions because of the smaller Cl radius resulting in a diminished halide-halide overlap.…”

Variational Monte Carlo study of a spin-1/2 Heisenberg antiferromagnet in magnetic fields

“…Recently, the fabrications of a new family of SSAF's with small exchange constants J 0.57 − 8.5 K, (5CAP) 2 CuX 4 and (5MAP) 2 CuX 4 with X=Cl or Br [2,3], have stimulated the exploration of high field properties of the SSAF by using spin-wave theory [4], variational approach [5], and exact diagonalization [6].…”

Path Laplacian operators and superdiffusive processes on graphs. II. Two-dimensional lattice

“…Square lattices are ubiquitous in many real-world physical systems. It is frequently used to describe the spin-1/2 antiferromagnetic Heisenberg model in a variety of materials [28,19,3,11]. It is also the preferred model for two-dimensional (2D) gases and optical lattices [5,21,18,1,25].…”