Low-Temperature Magnetic Anisotropy inAl2O3:

Abstract

Magnetic-anisotropy measurements on AI2O3: V 3+ single crystals have been made with a sensitive torsion balance at temperatures between 1.5-5°K. A least-squares method was used to fit the theoretical expression for Ax( =X-L~"X||) to the data. A% was found to be much more sensitive to gs. and 5, the zero-field splitting, in this temperature range than at higher temperatures. This sensitivity permitted a new determination of these parameters, with the results gx= 1.744^0.014 and S=7.97d=0.10 cm" 1 . The value of 5=7.97 cm -1 resulted in a new value for the spin-orbit coupling constant of X = 87±l cm" 1 . Finally, we obtain the temperature-independent value of % J-in good agreement with the experimental results.A general formula has been derived for Mossbauer absorption spectra of magnetically ordered systems in the presence of electron spin relaxation. The calculation is independent of any particular model of the magnetic spin system and the result is expressed in terms of magnetic spin correlation functions. The leading nonvanishing terms describing line broadening due to spin fluctuations are evaluated explicitly, and a relatively simple result is obtained for the special case of a scalar spin-spin interaction. Line shapes are in general complex, but can display Lorentzian or Gaussian behavior in certain cases.