Magnetic antiferromagnetic modulated

Fig. 39. The different magnetic structures of HoNi2 B2C as determined by neutron scattering, (a) Commensurate antiferromagnetic, (b) incommensurate restructure (spiral) with the modulation vector T2 = (0.0,0.916) and (c) proposal how the incommensurate a -structure looks like (Loewenhaupt et al. 1997). Its modulation vector is...

Measurements of the temperature dependence of x indicate the onset of antiferromagnetic ordering in UPd2Ge2 below 139 K (Ptasiewicz-Bak et al. 1981). Results of neutron diffraction measurements point to a longitudinally modulated structure with an amplitude of 2.80jub and a propagation vector [0, 0, ]. Magnetic moments were found only on the U atoms. 

The antiferromagnetic spin structure of YbNiAl was determined by neutron dif action experiments. Below Tn = 2.9K a sinusoidal modulated structure with an amplitude of /4=1.9(2))1b is observed (Ehlers et al. 1997). The magnetic propagation vector is m = [0.779(1)00], and the ytterbium magnetic moments lie perpendicular to the hexagonal c-axis. These investigations are paralleled by a detailed study of Al nuclear spin-lattice relaxation measurements (Fay et al. 1997). 

Fig. 23. Magnetic-field dependence of the enhanced linear spediic-heat coefficient y. Open circles were taken from Marcenat (1986) and squares from Bredl (1987). The peak in y near 2 T is related to the phase transition from the paramagnetic (i.e., antiferroquadrupolar) to the modulated antiferromagnetic phase. The line is a guide to the eye. Filled squares result from de Haas-van Alphen measurements (Joss et al. 1978). The points were calculated from the measured cyclotron masses on the assumption that the mass enhancement going from LaB to CeB is roughly isotropic over the...

The anisotropy of the RKKY interaction usually leads to rather complex magnetie struetures. In particular, nesting of the Fermi surface can have dramatic effects. An exemplary system is CeAlj (Steglieh et al. 1979b) its spin arrangement displays a type-II antiferromagnetic structure in which the magnetic moments are parallel to [111] and point into opposite directions on the lattice sites (0,0,0) and (3,5,5). The moments are modulated by an ineommensurate wavevector (i + t, 5 — t, 5) with t = 0.11 (Barbara et al. 1977). 

Fig. 56. Magnetic phase diagram of CeAlj as derived from thermal expansion (solid lines, Schefzyk et al. 1985a) and neutron diffraction ( , O, dashed lines Barbara et al. 1980). Dotted line is an interpolation (schematic) II, type-II antiferromagnetic structure M, modulated structure PM, paramagnetic phase.

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