Proton Magnetic Resonance Study of Magnetic Ordering in Two Cupric Salts

The shifts and the widths of the proton magnetic resonance lines in two Cu2+ salts have been studied to obtain information about the antiferromagnetic short-range order in these crystals. In Cu(NH3)4SO4·H2O, where the Cui+ spins order in antiferromagnetic linear chains, the resonance lines show a strong broadening at decreasing temperatures. This is explained by the decrease of the fluctuations of the Cu2+ spins due to the forming of antiferromagnetic clusters. The experimental results are in agreement with a simple model, relating the fluctuations and the susceptibility of the Cui+ spins. In Cu(NO3)2·3H2O measurements of the lineshifts show that the Cu2+ spins order antiferromagnetically in pairs. No broadening of the PMR lines is observed, which is explained by the absence of cluster forming.