The deep centers in evaporated ZnS : Ag thin films have been characterized by observation of the infrared quenching of photocapacitance using Schottky barriers. The photoionization energy of holes for transitions from Ag centers to the valence band edge is determined to be 0.56 eV at 300 K. The spectral distribution of the photoionization cross section of holes is obtained theoretically. It has been found that the magnitude of the photocapacitance quenching depends linearly on the intensity of the infrared illumination in the low-intensity range. The concentration profile of Ag impurities has been measured and is almost uniform throughout the depletion layer in the films.
Spontaneous magnetization as a function of temperature is investigated for a number of disordered Ni-Fe-Mo and Ni-Fe-W alloys using superconducting quantum interference device magnetometry, with a focus on the low-T behaviour as well as the critical exponents associated with the magnetic phase transition. While the low-T magnetization is found to be well described by Bloch's T 3/2 law, extraordinary enhancements of the spin-wave parameter B and the reduced coefficient B 3/2 = BT 3/2 C are observed with increasing Fe dilution as compared to conventional 3d ferromagnets, whereas the critical amplitudes are found to decrease systematically. Recent locally self-consistent calculations of finite-temperature spin dynamics in a generic diluted magnet provide an understanding in terms of two distinct energy scales associated with weakly coupled bulk spins in the ferromagnetic matrix and strongly coupled cluster spins. In view of the similar behaviour observed in diluted magnetic semiconductors and other ferromagnetic alloys, it is proposed that these distinctive features corresponding to the three important temperature regimes provide macroscopic indicators of signature effects of spin clustering on the magnetization behaviour in disordered ferromagnets.
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