Abstract--Samples of Na-saturated, Upton montmorillonite were prepared with different contents of water (H20 or D20) by: (1) adsorption of water from the vapor phase at a specific value of p/p*, the relative humidity, (2) adsorption of water from the vapor phase at p/p* = 1.0 followed by desorption of the water into the vapor phase at a specific p/p* < 1.0, and (3) adsorption of water from the liquid phase followed by desorption of the water into the vapor phase at a specific p/p* < 1.0. Water adsorbed initially from the vapor phase was called V-adsorbed water, and water adsorbed initially from the liquid phase was called L-adsorbed water. The water contents of these samples were determined by gravimetric analysis, the c-axis spacings by X-ray powder diffraction, the O-D stretching frequencies by IR spectroscopy, and the heats of immersion by differential microcalorimetry. No difference was found between V-adsorbed and L-adsorbed water; however, if the final water content was established by adsorption, the system was in a different state than if the final water content was established by desorption. In particular, hysteresis was observed in the following properties: the relative humidity of the adsorbed water, the O-D stretching frequency in this water, and the degree of order in the stacking of the clay layers. The only property that did not exhibit hysteresis was the heat of immersion. Apparently, hysteresis occurred because the orderliness of the system was not reversible, and, thus, any property that depended on orderliness was hysteretic.

For NiFe/FeMn bilayers, the correlation among the exchange field, the coercivity, the training effect, the hysteretic effect of the angular dependence of the exchange bias, and the rotational hysteresis loss has been studied as a function of the antiferromagnet layer thickness t AFM . With increasing t AFM , all these quantities undergo nonmonotonic variations, except for the monotonic change in the exchange field. The maximal values of the coercivity, its relative change, and the rotational hysteresis loss are almost located at the same t AFM of 3.8 nm. The maximal values of the relative change in the exchange field and of the hysteretic effect of the angular dependence are located at 2.5 and 3.0 nm, respectively. The rotational hysteresis loss and the hysteretic behavior of the angular dependence of the exchange bias have different characteristics. The variations of all physical quantities with t AFM can be ascribed to the irreversible reversal of the antiferromagnet spins, which are governed by the Arrhenius-Néel law, except for that of the rotational hysteresis loss.