No abstract

Electron spin relaxation data from five ferric proteins are analyzed in terms of the fractal model of protein structures. Details of this model are presented. The results lead to a characterization of protein structures by a single parameter, the fractal dimension, d. This structural parameter is shown to determine the temperature dependence of the Raman electron spin relaxation rate, which varies as T3 + 2d. Computations of d are made using x-ray data for 17 proteins. The results range from d = 1.76 for lysozyme to d = 1.34 for ferredoxin. These values are compared with values of d obtained from the present electron spin relaxation data on five ferric proteins. Typical results are d = 1.34 +/- 0.06 from relaxation data and 1.34 +/- 0.05 from x-ray data for ferredoxin; d = 1.67 +/- 0.03 from relaxation data and 1.66 +/- 0.05 from x-ray data for ferricytochrome c. The data thus support the theoretical model. Applications of this spin resonance technique to the study of changes in protein conformation are discussed.

Multilayered Co/Pd thin films were prepared by sequential electron-beam evaporation of Co and Pd onto Si substrates at room temperature. The thicknesses of the Co sublayer and of the Pd sublayer were varied between 2.0–10.3 and 4.5–22.3 Å, respectively. As the Pd sublayer thickness was varied at constant Co thickness, broad maxima in the saturation magnetization Ms and intrinsic perpendicular anisotropy energy Ku were observed at a Pd thickness of about 10 Å. At this maximum, Ms per Co volume is larger than the saturation magnetization of bulk Co. This is believed to be caused by the polarization of the Pd atoms within about 10 Å of the Co layer. Ku and Ms per Co volume both decrease with increasing Co layer thickness.

The tensile strength of test pieces made from natural rubber vulcanizates drops abruptly at a critical temperature which can vary from 40 to 130°C. This variation in critical temperature is shown here to be a result of the variation in critical cut length with temperature. When the naturally occurring flaws in the test piece are smaller than the critical cut length, high tensile strength values occur, but when the flaws are longer than the critical cut length, low tensile strength values occur. The critical cut length decreases as the temperature increases, and the abrupt drop in tensile strength occurs as the critical cut length reaches the natural flaw size in the test piece. The natural flaw size in tensile test pieces depends on the sharpness of the cutter, and for tensile strength measurements at elevated temperature, it is shown that even a slightly blunt cutter may give markedly different results from a sharp one.

The Hall effect is a useful probe of the magnetization in thin metallic films since the signal is inversely proportional to the film thickness. Previously, the minimum in the coercivity, derived from the Hall hysteresis loop as a function of the angle of the applied field, has been used to determine the hard axis of magnetic thin films. A vibrating sample magnetometer can be used in this fashion if coherent rotation is the magnetization reversal mechanism. However, we show that even in the case of the Stoner–Wohlfarth model, the minimum of the Hall coercivity does not coincide with the hard axis. We propose an alternative method for determining the easy axis, which is independent of the magnetization reversal mechanism and does not require measuring the entire hysteresis loop. In addition, since for an arbitrary orientation of the applied field the measured Hall voltage will contain components due to magnetoresistance as well as the Hall effect, it is possible to extract a measure of the in-plane and perpendicular magnetization. Using this information, we derive a method of producing vector plots that show the magnitude and direction of the magnetization as a function of applied field for various applied-field orientations. Examples using CoCr and TbFe will be presented.