Abstract
Submillimeter ESR of (NH4)2CuCl4·2H2O (Cl-salt), (NH4)2CuBr4·2H2O (Br-salt), CuCl2·2H2O and Cu(NH3)4SO4·2H2O (CTS) has been measured down to liquid helium temperature region by the apparatus using 337 μm wave of HCN laser and pulsed high magnetic fields up to 500 kOe. Each salt contains exchange-coupled inequivalent spin sites and so-called exchange splitting has been observed at room temperature. At liquid helium temperatures intensities of the two split lines are quite different and weaker line has shown a remarkable shift in Cl-salt, CuCl2·2H2O and CTS. In Br-salt only single line has been observed. These phenomena can be successfully explained by the molecular field theory. Inequivalent spins in CTS have been deduced by the theory to be anitiferromagnetically coupled while the coupling in Cl-, Br-salts and CuCl2·2H2O are ferromagnetic.
