and which thus rapidly increases as the incommensurate-paraeiectric transition T T is approached. In the vicinity of the defects the phase will be pinned, whereas in the region between the defects we shall have large phase fluctuations (i.e., the modulation wave will be rough). The radius of the "pinned" region (where the root mean square phase fluctuation amplitude is smaller than TT/2) slowly decreases with increasing temperature, whereas the "floating" part (where the root mean square phase fluctuation amplitude exceeds TT/2) increases with the mean distance between "pinning" defects. The fraction £ of the pinned nuclei giving rise to the broad NMR line thus decreases critically as the incommensurateparaeiectric transition temperature is approached;Thus NMR lines from the pinned and the floating regions should be observed below T l if the number of defects is not too large.The experimental data show that y ~ 2. The appearance of the sharp NMR lines is thus due to a decrease in the strength of the phase pinning potential of impurities with increasing temperature and the corresponding increase in the mean distance between pinning defects. This increase in distance results in an increase in the mean square vibration amplitude of the modulation wave, which thus becomes "rough" and float-Primary electrons with sufficient energy impinging on a solid generate low-energy secondary electrons via a cascade process. Within the cascade process, the number of hot electrons is multiplied due to scattering of the excited elec-ing over an increasing part of the crystal. The observed phenomenon is thus similar to a roughening transition. Similar effects should be observable close to T l in other incommensurate systems provided the pinning defect concentration is not too large. . trons primarily by conduction-band electrons. 1 In the absence of spin-dependent scattering processes it had been thought that the spin polarization of the secondaries directly reflected the net spin polarization of the conduction bands, P = («t The energy-resolved spin polarization P of secondary electrons from Ni(110) has been measured with high energy resolution. At the lowest kinetic energy p reaches a maximum of (17 ±2)% which is significantly higher than the mean conduction-band polarization (5.5%). Within about 3 eV towards higher kinetic energy the spin polarization decreases to about 8% and displays pronounced structures at higher energies. Spindependent electron-hole-pair excitations are suggested to be responsible for the observed spin polarization.

West GermanyAngle-and spin-resolved photoemission spectra from Ni(llO) have been measured in the temperature range 0.5^ T/T c^ 0.94. The data cannot be reconciled either with the predictions of local band theory assuming a temperature-independent exchange splitting or with a pure Stoner model. It is concluded that the exchange splitting decreases with increasing temperature and that spin fluctuations strongly influence the photoemission line shapes.

No abstract

No abstract

No abstract