Magnetic dipole interactions in dysprosium ethyl sulphate - I. Susceptibility and specific heat between 20 and 1°K

Measurements have been made of the magnetic susceptibility and the magnetic contributions to the specific heat of dysprosium ethyl sulphate, at temperatures between 20 and 1°K. It is shown that below about 3°K these properties, and also the earlier optical rotation measure­ments of Becquerel et al., can be accounted for satisfactorily in terms of a doubly degenerate ground state of the magnetic ions, with spectroscopic splitting factors parallel and perpen­dicular to the crystal axis g1 = 10.8 and g┴ = 0, together with an unusually strong coupling between the ions arising from magnetic dipole-dipole interaction. The effect of other inter­actions is shown to be small. Because of this, and the extreme anisotropy of the g-tensor, the properties of this substance at very low temperatures (~ 0.1°K) should closely resemble those of a classical Ising model with known, dipolar forces between the ions. At temperatures above 3°K other states of the ions become populated and it is shown that the first of these lies at an energy of (23 ± 3) k, in good agreement with other experiments.