Light Figures and Surface Structures Revealed by Chemically Etched Germanium Single Crystals

Light figures projected on a plate screen from germanium single crystals, polished mechanically and etched with various chemical reagents, are examined in order to find out light figures or etching directions suitable for the orientation determination. In. formation regarding surface structures of germanium single crystals developed by mechanical polishing and by chemical etching has been obtained from the analysis of the observed light figures and from microscopic observations of crystal surfaces. It has been found that distinct light figures suitable for the orientation work are obtained by a short time etching with concentrated nitric acid plus water (1 : 1 and 3 : 7 ; 70℃), with concentrated nitric acid plus water plus hydrofluoric acid plus silver nitrate (45 cc+45 cc+10 cc+50 or 20 mg, and 20 cc+40 cc+40 cc+2 g), with hydrofluoric acid plus hydroperoxide plus water (1 : 1 : 4), and with 30 percent hydroperoxide (100℃). Among these etchants, hydrofluoric acid plus hydroperoxide plus water (1 : 1 : 4) is most suited for accurate orientation determination. Generally, crystal faces developed by etching have been found to be those belonging to the principal crystal zones, but dilute nitric acid heated at 70℃ develops some additional high-index crystal faces belonging to a high-index crystal zone. There is a tendency that low-index crystal faces appear by a short time etching and high-index ones by a prolonged etching. It is to be added that relatively clear light figures are obtained on germanium crystals as polished with silicon carbide powder

Magnetic Hysteresis in Annealed Nickel-Cobalt Alloys

The magnetic hysteresis loops have been determined ballistically on annealed nickel-cobalt alloys covering the whole composition range, and their shape, remanence (I_R), and coercive force (H_C) have been studied. Generally, the hysteresis loops of γ-phase (face-centred cubic) alloys are narrow (low H_C) and steep (high I_R), those of ε-phase (close-packed hexagonal) alloys are wide (high H_C) and flat (low I_R), and those of γ+ε-phase alloys are intermediate between the two former. The hysteresis loops of γ-phase alloys containing more than about 25 percent cobalt usually take an abnormal shape like those of perminvars and permalloys. It is pointed out that such abnormal hysteresis loops may be explained by the occurence of an additional uniaxial anisotropy along the direction of magnetization vectors during annealing, which may also be responsible for the effect of magnetic annealing on ferromagnetic solid solutions, as noted recently by us^. The observed I_R values for γ-phase alloys are shown to lie between the two extreme theoretical values derived assuming either that all of the directions of easy magnetization in every crystal grains are energetically isotropic or that only one of them is preferred. H_C as a function of the composition is discussed in terms of the magnetocrystalline anisotropy, magnetoelastic energy and induced uniaxial anisotropy. It is also pointed out that both I_R and H_C in ε-phase alloys may be influenced by the presence of free magnetic poles at grain boundaries