Abstract
The results are reported of magnetic field-dependent neutron diffraction experiments on polycrystalline inert-gas condensed holmium with a nanometre crystallite size (D = 33 nm). At T = 50 K, no evidence is found for the existence of helifan(3/2) or helifan(2) structures for the nanocrystalline sample, in contrast with results reported in the literature for the single crystal. Instead, when the applied field H is increased, the helix pattern transforms progressively, most likely into a fan structure. It is the component of H which acts on the basal-plane spins of a given nanocrystallite that drives the disappearance of the helix; for nanocrystalline Ho, this field is about 1.3 T, and it is related to a characteristic kink in the virgin magnetization curve. For a coarse-grained Ho sample, concomitant with the destruction of the helix phase, the emergence of an unusual angular anisotropy (streak pattern) and the appearance of novel spin structures are observed.
Highlights
While the spin structures of most of the heavy rare earth metals are well understood in zero magnetic field (Koehler, 1965), the situation becomes more complicated once an external magnetic field is applied (Jensen & Mackintosh, 1991)
At T = 50 K, we have studied by means of neutron diffraction along the (000) forward direction the magnetic field-dependent spin structure of polycrystalline inert-gas condensed Ho with an average crystallite size of D = 33 nm
As the applied magnetic field H is increased from zero to 5 T, we observe that the Debye–Scherrer ring, which is characteristic for magnetic neutron diffraction on the antiferromagnetic helix, ‘breaks up’ in the direction perpendicular to H and that the scattering intensity becomes progressively concentrated along the direction parallel to H
Summary
While the spin structures of most of the heavy rare earth metals are well understood in zero magnetic field (Koehler, 1965), the situation becomes more complicated once an external magnetic field is applied (Jensen & Mackintosh, 1991). This is so for the case of holmium (Koehler et al, 1966), where the application of a field (Koehler et al, 1967) results in the emergence of a number of complicated magnetic structures, e.g. the so-called helifan phases (see below) (Jensen, 1996).
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