Opening of the EPR bottleneck in amorphous GdxY0.33-xAl0.67

The temperature dependence of the EPR linewidth and g shift are measured in amorphous evaporated films of GdxY0.33-xAl0.67 with 0.0008<x<0.33. Both the g shift and the Korringa slope of the linewidth-versus-temperature curve increase with decreasing x in a fashion which can be fitted to classic EPR bottleneck theory. This procedure yields the spin-lattice relaxation rate for the conduction electrons consisting of a "structural" term (1.3-6) × 1011 Hz and a term proportional to Gd concentration of 1×1013x. The latter is within 50% of the value in the crystalline counterpart, but the former is larger by a factor of 3 to 15, showing for the first time (aside from studies on liquids) the effect of amorphous structure on this relaxation rate. Similarity of unbottlenecked g factors and Korringa slopes of amorphous and crystalline materials suggest that the conduction band is not strongly affected by structure. © 1981 The American Physical Society.