Cu(H2o)(2)(C2h8n2)So4: A Quasi-Two-Dimensional S=1/2 Heisenberg Antiferromagnet

The experimental results of the susceptibility, specific heat, magnetization, and electron spin resonance of Cu(H2O)(2)(C2H8N2)SO4 are reported. Despite the triangular arrangement of chemical bonds, the system is identified as an S=1/2 Heisenberg antiferromagnet where the dominant exchange coupling J/k(B)approximate to-1.4 K is mediated by a square network of hydrogen bonds. The long-range ordering observed at T-N=0.91 K is proposed to be Neel type. The possibility of tuning the strength of the exchange couplings in various directions is discussed.