2009/03/13 by F. Xiao, F. M. Woodward, C. P. Landee +14
Chemistry · Materials Science · Physics and Astronomy · #Advanced Condensed Matter Physics #Chemistry #Condensed matter physics #Crystallography #Magnetic field #Magnetism in coordination complexes #Magnetization #Order (exchange) #Physics #Physics of Superconductivity and Magnetism #Quantum mechanics #cond-mat.mtrl-sci #cond-mat.str-el
paper · pdf · doi:10.1103/physrevb.79.134412
Accepted for publication in Physical Review B
arxiv created 2009/03/13 · openalex publication_date 2009/04/09 · arxiv updated 2015/05/13 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The magnetic properties of a family of molecular-based quasi-two-dimensional S=1/2 Heisenberg antiferromagnets are reported. Three compounds, [Cu(pz)2(ClO4)2, Cu(pz)2(BF4)2, and [Cu(pz)2(NO3)](PF6)] contain similar planes of Cu2+ ions linked into magnetically square lattices by bridging pyrazine molecules (pz=C4H4N2). The anions provide charge balance as well as isolation between the layers. Single crystal measurements of susceptibility and magnetization, as well as muon-spin-relaxation studies, reveal low ratios of N'eel temperatures to exchange strengths (4.25/17.5=0.243, 3.80/15.3=0.248, and 3.05/10.8=0.282, respectively) while the ratio of the anisotropy fields HA (kOe) to the saturation field HSAT (kOe) are small (2.6/490=5.3\ifmmode×\else\texttimes\fi10^\ensuremath-3, 2.4/430=5.5\ifmmode×\else\texttimes\fi10^\ensuremath-3, and 0.07/300=2.3\ifmmode×\else\texttimes\fi10^\ensuremath-4, respectively), demonstrating close approximations to a two-dimensional Heisenberg model. The susceptibilities of ClO4 and BF4 show evidence of an exchange-anisotropy crossover (Heisenberg to XY) at low temperatures; their ordering transitions are primarily driven by the XY behavior with the ultimate three-dimensional transition appearing parasitically. The PF6 compound remains Heisenberg type at all temperatures, with its transition to the N'eel state due to the interlayer interactions. Effects of field-induced anisotropy have been observed.