The spin-orbit induced electric field gradient at the nuclear site of 183 Os and 183 Re impurities in Fe and of 191 Pt and 186 Ir impurities in Ni was determined for ͓100͔, ͓110͔, and ͓111͔ orientations of the magnetization. The measurements were performed on single-crystal samples using nuclear magnetic resonance on oriented nuclei and modulated adiabatic fast passage on oriented nuclei. In the Ni experiments the electric field gradient was also determined for other orientations of the magnetization in the ͑110͒ plane. These data, together with previous results on the 5d impurities, provide the first fairly complete data set on the spin-orbit induced electric field gradient in cubic Fe, Co, and Ni. Our results establish in particular that the effect depends in general considerably on the direction of the magnetization. We summarize the present knowledge of these electric field gradients, their magnitude, their systematics, and the form and magnitude of their dependence on the direction of the magnetization. The properties of the effect are explained within the tight-binding model in terms of the spin-orbit induced deformation of the electron distribution. We also present and discuss data on the dependence of the hyperfine field on the direction of the magnetization, which was found to be smaller than 10 Ϫ3 , and on the inhomogeneous broadening of the electric field gradient.
[2,3]. For the system AuFe the EFG could also be detected with spin echo measurements on 197 AuFe [8,9].In principle, the EFG in a cubic ferromagnet can arise from magnetostriction and from unquenched local moments. As the observed EFG's are much larger than an EFG due to magnetostriction could be, it was early adopted that the main source is the unquenched orbital momentum [13][14][15]. From theoretical calculations Demangeat [13] postulated that EFG's originating from an unquenched orbital momentum should strongly depend on the direction of magnetization with respect to the crystallographic axes. Based on experimental results of NMR measurements on 191,193 Ir in Fe single crystals [5] and NMR on orientated nuclei (NMR-ON) measurements on 192 Ir in a Ni single crystal [4] it was concluded, however, that such a dependence does not exist. Another theoretical approach was considered by Gehring and Williams [15]. In the general framework of their model, the EFG may, depending on the relative sizes of spin-orbit coupling, the crystal field, and the exchange splitting, depend on the direction of the magnetization with respect to the crystal axes, or not. Led by the experiments suggesting the EFG to be invariant, they concluded that the effects of the crystal field can be neglected, which leads to an invariant EFG.Recent NMR-ON and modulated adiabatic fast passage on oriented nuclei (MAPON) measurements on Z 77 188 Ir in an Fe single crystal showed a strong dependence of the EFG on the direction of magnetization with respect to the crystallographic axes [11]. In these experiments no special attention was directed to the widths of the EFG distributions, as there was no theoretical hint that the EFG width could be directional dependent. The measured ratio, G ͓͑100͔͒ ͞G ͓͑111͔͒1.5͑5͒, showed, however, that the width could be larger for M k ͓100͔ than for M k ͓111͔. On the other hand, these data were not conclusive because of the too large statistical error. Thus, it was concluded that the EFG is sharp and that the distribution is introduced by the nonperfect surface quality of the used single crystal.
A special experimental setup was used to study the equilibrium gas composition after interaction of propene with pure thin polycrystalline nickel films and nickel films precovered with hydrogen under ultrahigh vacuum conditions. Isothermal reaction mass spectrometry allows the analysis of the gas phase composition under equilibrium conditions. The analyzed gas phase consists of desorbed reaction products formed in the adsorbate phase after adsorption of propene on nickel films at 273 K. This technique was combined with thermal desorption spectroscopy and measurements of adsorption-induced changes in the electrical resistance of the polycrystalline films. After interaction with pure nickel films, in addition to propene, hydrogen, methane, propane, and butane could be detected as reaction products. The interaction of propene with nickel films precovered with hydrogen leads to a higher yield of butane and additionally to the formation of pentane. Thermal desorption experiments carried out after adsorption of propene at 77 K show only desorption of hydrogen, when the propene coverage was small. At higher coverages also propene desorbed.
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