13 research outputs found
Demagnetization factors of the general ellipsoid: An alternative to the Maxwell approach
No full textA transparent, exhaustive, and self-contained method for the calculation of the demagnetization tensor of the uniformly magnetized ellipsoid is presented. The method is an alternative to the established Maxwell derivation and is based on a Fourier-space approach to the micromagnetics of magnetized bodies. The key to the success of the procedure lies in the convenient treatment of shape effects through the Fourier representation. The scaled form of the demagnetization factors which depends on two dimensionless aspect ratios is argued to be their natural integral representation. Amongst other advantages, it allows for the immediate implementation of symmetry arguments such that only one of the principal factors needs to be computed. The oblate and prolate ellipsoids of revolution are examined from the same general point of view. The demagnetization factors for these distinct types of spheroid are seen to be related by analytic continuation of well-known Gaussian hypergeometric functions
LE'lTER TO THE EDITOR Influence of long-range correlated impurities upon the phase transition in model superconductors
No full textAbstract. The influence of long-range correlated quenched impurities of a power-law decay type upon the phase transition in a model system of a superconductor is investigated. Direct renormalisation group &-analysis yields a fixed point which is stable over a domain in a specific parameter connected with the long-range character of the correlations. The critical exponents are calculated to first order in E. The existence of a stable fixed point is interpreted as signalling a second-order phase transition near four dimensions of space. The purpose of this Letter is to extend the Halperin-Lubensky-Ma (HLM) investigation (Halperin ef a1 1974) by introducing long-range correlated quenched impurities of a special type (Weinrib and Halperin (WH) 1983) by means of a renormalisation-group (RG) direct perturbation &-analysis (Wilson and Kogut 1974). The features of the same model with short-range correlations between the impurities have already been outlined by Boyanovsky and Cardy (1982) for n = 2 and by Uzunov et a1 (1984) for any n (n/2 is the number of the components of the complex-order parameter field). Taking the latter work as a basis, we specify the effective Hamiltonian X=(-H/k,T) of the d-dimensional model system a
