No abstract

No abstract

Spin-lattice relaxation time (/'1) of Fe 3+ ions has been measured in four borate glasses doped with 0.25, 0.5, 1 and 3 wt.% Fe203 by the modulation method over the temperature range 5-250 K. In the three less concentrated samples, ir was observed that T; -I oc T at intermediate temperatures. This is explained in terms of a relaxation mechanism involving TLS (Two Level Systems). At higher temperatures, the temperature dependence of Ti ~ is slowed down by cross-relaxation. In the most concentrated sample, the exchange interaction plays a dominant tole leading to a very different relaxation-time behaviour, described well by the Bloembergen and Wang three-reservoir model.

We present electron-spin-resonance data obtained on finite magnetic chains of CH3NMniCd Cl, (TMMC-Cd) for x =0. 02, 0.09, and 0.2. The measurements were developed with the microwave field either parallel or perpendicular to the magnetic field. The longitudinal relaxation time was also measured in the x =0.02 and 0.09 samples. All our experimental results show a noticeable inAuence of the impurities on both the line shape and linewidth, contrary to previously published data. New nuclear magnetic resonance data dealing with high-frequency proton relaxation rates are also presented. A full treatment using the memory-function formalism has been carried out to account for the significant difference observed between pure and doped samples. Our experimental data are satisfactorily described by this theory and the model of correlation functions for finite chains.