arXiv subjects
Publications and source records attributed to Y. N. Skryabin.
The effects of rare regions on the critical properties of quantum antiferromagnets with hidden degrees of freedom within the renormalization group is discussed. It is shown that for ``constrained'' systems the stability range on the phase diagram remains the same as in the mean-field theory while for ``unconstrained'' systems the stability range is effectively decreased.
Taking into account the long-ranged spin interactions due to weak localization effects in disordered itinerant ferromagnets the scattering of both electrons and neutrons on critical spin fluctuations near quantum phase transition is considered. It is shown that for the case of low electron density, when k_F ξ\ll 1, where k_F is the Fermi momentum and ξis the magnetic correlation length, the transport cross section of electrons is proportional to conventional critical fluctuations in absence of weak localization effects. However, the intensity of the multiple small-angle neutron scattering becomes exponentially small as compared with the intensity of the multiple scattering by conventional critical fluctuations.
The small-angle scattering of neutrons on large scale inhomogeneities of two-component systems in refraction range is considered. We supposed, that neutrons acquire phase shifts describing by the Gaussian distribution function. It is shown that the average cross section of scattering contains two contributions. The first contribution describes the diffraction and in the asymptotic limit of large transfer momentum this contribution is proportional to q^{- Δ}, where 2 \leq Δ\leq 4. The second contribution is similar to the Fraunhofer diffraction, which in the asymptotic limit of large transfer momentum is proportional to q^{-3}.
The influence of disordering upon critical behavior of the system with hidden degrees of freedom is considered. It is shown that there is a tricritical behavior in the constrained system, while in the unconstrained system only phase transitions of the second order occur.
The conclusions arising from the multiple small angle neutron scattering theory, developed recently by S.V. Maleyev, R.V. Pomortsev and Y.N. Skryabin [Phys. Rev. B 50 7133 (1994)] for the value of Born parameter more than 1, are experimentally confirmed by magnetic scattering from domain structure of pure Fe and Ni, as well as Fe_{65}Ni_{35} alloy. The crossover from multiple refraction to multiple Fraunhofer diffraction is found to be at a critical thickness L_0, where dependence of the neutron beam broadening w on sample thickness L changes from law L^{1/2} to law L.