Magnetic Dipole Interactions in Dysprosium Ethyl Sulphate. III. Magnetic and Thermal Properties Below the Curie Point

• Published in: Proceedings of the Royal Society of London. Series A, Mathematical and physical sciences Mathematical and physical sciences, 1968-09, Vol.306 (1486), p.335-353
• Main Authors: Cooke, A. H., Edmonds, Donald T., Finn, C. B. P., Wolf, W. P.
• Format: Article
• Language: English
• Subjects: Crystals; Domain walls; Dysprosium; Ellipsoids; Entropy; Magnetic fields; Magnetization; Relaxation time; Transition points; Transition temperature
• ISSN: 1364-5021; 0080-4630; 1471-2946; 2053-9169
• DOI: 10.1098/rspa.1968.0154

The thermal and magnetic properties of dysprosium ethyl sulphate have been measured at temperatures below its Curie temperature of 0⋅13 °K. The ferromagnetism is shown to be due almost entirely to magnetic dipole interactions which are highly anisotropic corresponding to a zero magnetic g-value perpendicular to the c-axis. The system thus approximates closely to a ferromagnetic Ising model. Because of demagnetizing effects the low field proper­ties are dominated by the formation of domains, which are shown to be long and thin with unusually abrupt domain walls. Measurements of the initial susceptibility at frequencies between 25 and 900 c/s show marked relaxation effects which are interpreted in terms of both domain wall motion and single spin reversals. A discussion is given of the general problem of finding the real and imaginary susceptibility components in systems with strong dipolar interactions. In favourable cases, such as dysprosium ethyl sulphate, it is possible to find a shape-independent quasi-static susceptibility which corresponds to the response of the system in the absence of domain wall motion and demagnetizing effects. Values for the spin-reversal relaxation time are found to be of the order of tens of microseconds which is surprisingly short in view of the absence of non-diagonal terms in the spin-spin interactions.