On the theory of spin fluctuations around the magnetic instabilities - Effects of zero-point fluctuations

Effects of temperature variation of the zero-point spin fluctuations on the self-consistent renormalization (SCR) theory of spin fluctuations around t he magnetic instabilities are discussed. In two and three dimensional ferro magnets and three dimensional antiferromagnets the effect is mostly to reno rmalize the mode-mode coupling constant. The renormalized value, correspond ing to the experimental value, has a finite upper bound corresponding to a divergent mean field value. In two-dimensional antiferromagnets the critica l behaviors of the staggered susceptibility and the nuclear spin-lattice re laxation rate are modified by logarithmic corrections while this correction hardly appears in those of the electrical resistivity and the specific hea t. The temperature variation of the mean square local amplitude of the spin density around the magnetic instability is studied by using a simple model for the dynamical susceptibility and is applied to discuss a general trend in the magneto-volume effects in weak itinerant magnets. Possible origins of the large thermal expansion and the large low temperature coefficient of the specific heat in magnetically frustrated systems are also discussed.