Abstract
Four series of observations carried out in the Kamerlingh Onnes Laboratory on Cu·2O crystals are reviewed. The magnetization curves confirm the general picture given by the theoretical analysis of Gorter and Haantjes. At the lower temperature a sharp threshold field is found in the crystallographic plane with a minimum value of 6500 φ; at higher temperature its value increases somewhat.
Specific heat measurements reveal the existence of a short-range order tail above the sharp Néel temperature at which antiferromagnetism vanishes.
In the investigations on proton magnetic resonance a sharp transition is found between a nonsymmetrical paramagnetic resonance diagram and a symmetrical resonance diagram characteristic for antiferromagnetism. In this way it is found that the Néel temperature depends on the direction of the magnetizations.
It is possible to follow the turn-over of the magnetizations near the threshold field. The position of the protons and the nature of the sublattices have been determined. The sublattices do not exchange position within sec. Microwave resonances have been observed at 9400 and at 4000 megacycles/sec. The absorption bands are confined to the neighborhood of the turn-over fields. General agreement with Ubbink's theoretical treatment is found.
DOI:https://doi.org/10.1103/RevModPhys.25.332
©1953 American Physical Society