The magnetic structure of holmium: Pt. 2

A spin-slip model of the helical antiferromagnetic phase of holmium is seen to provide a good description of both elastic neutron diffraction and ultrasonic velocity measurements close to the commensurate lock in transition (Tsub(c) = 17.8 K). The measurements show that contained within the smooth thermal evolution of the spin-slip structure, there exist 'special' structures possessing an average spin-slip spacing, b, given by b = 3n - 1 layers. These structures, which occur at temperatures of 97.4, 40.5, 24.5 and 19.8 K, are shown to break the hexagonal symmetry. Selection rules governing the relationship between anomalous elastic constant behaviour and these special structures are derived. At higher temperatures approaching the paramagnetic phase (Tsub(N) ∼ 133 K) the validity of the spin-slip model is seen to be increasingly questionable. (author)