Proton Magnetic Resonance Study of Magnetic Ordering in Two Cupric Salts

Abstract

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 Cu_i⁺ 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 Cu_i⁺ 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.