Paramagnetic short range order in holmium

Complete text of publication follows. Below TN ∼ 133 K the magnetic moments of holmium order in an incommensurable helifan-structure with propagation vector q ∼ 0.275 c*. At about 20 K the magnetic structure changes to a commensurable conical shape (Koehler et al 1966, Felcher et al 1976, Pechan and Stassis 1984). The critical region near TN has been investigated by Eckert and Shirane, 1976. They determined an critical exponent β = 0.39(4). Using the flat-cone diffractometer E2 and the instrument E6 with a linear multidetector at BENSC complete planes of the reciprocal space have been studied to get more information about the magnetic correlations. In the critical region the distributions of the magnetic diffuse scattering around superstructure Bragg positions can be described by an elliptical lorentzian law. At higher temperatures the measured data were fitted by an extended molecular field (MF) theory and a renormalized temperature as parameter. The q-dependent susceptibility is compared with the conventional MF theory on interaction parameters wick are derived from the spin wave dispersion. (author)