Michiyoshi Oku

Renormalized Field Theory of Random Magnetic Mixtures with Competing Spin Anisotropies. I

Les points fixes des fonctions β et les valeurs propres de la matrice B de la partie I sont calcules dans la partie II. On confirme que les 256 points fixes des melanges du type Ising-XY non symetriques sont instables et que les 128 points fixes des melanges du type Ising-Ising non symetriques deviennent instables. Les points tetracritiques des systemes magnetiques etudies ne sont pas du second ordre

Gaussian Random Bond Problem for Annealed System in 1/n Expansion

Critical phenomena for the annealed n-vector model are studied in lin expansion by assuming that the exchange interactions between spins are fluctuating variables obeying the Gaussian distribution. It is shown that for an overall fluctuation of the interaction between spins the susceptibility never diverges at any finite temperature except for n~ = (spherical limit) and n = 1 (Ising) cases. On the other hand, if the fluctuation is restricted to only nearest-neighbor pairs, the susceptibility is proved to diverge at an appropriate transition temperature in the limit n~=. The critical exponent f in this case is shown to be the same as the spherical model value. Also the dependence of transition temperature on the strength of fluctuation is discussed.