The shape of the proton magnetic resonance lines in CuSO 4·5H 2O at temperatures down to 0.31°K

Abstract

The shapes of the proton magnetic resonance lines in a single crystal of CuSO 4·5H 2O have been measured between 20°K and 0.31°K, using a 3He cryostat for the temperature region below 1.2°K. Above about 3°K the line widths are roughly independent of the temperature. The different contributions to the line width in this temperature range, arising from intra-and inter molecular proton-proton coupling and from the dipolar interaction between protons and the Cu ions at ( 1 2 , 1 2 , 0) have been determined. The results agree with calculations based upon the geometry of the unit cell and with the estimated exchange frequency of the ( 1 2 , 1 2 , 0) ions. Below about 3°K some of the resonance lines show a marked broadening, which can be explained by a slowing down of the fluctuations of the magnetic moments located at the (0, 0, 0) positions. These magnetic moments are antiferromagnetically coupled in one dimension and show increasing short range order at lower temperatures. The field and temperature dependence of this type of broadening have been measured and agree approximately with a simple calculation which relates the proton resonance line width and the susceptibility of the (0, 0, 0) system. The reported experiments are a continuation of the measurements of the proton resonance line shifts in CuSO 4·5H 2O, rreported in a preceding paper 1).