The magnetic structure of erbium

The magnetic structure of erbium arises as a result of the competition between the long-range, two-ion interaction, which favours a periodic structure, and the magnetic anisotropy, which tends to align the moments along one of the crystalline directions, either in the basal plane or along the c axis. In the most complicated phase, there is a modulated moment both within the basal plane and along the c axis. This structure becomes more complex as the temperature decreases and the perturbation of the modulation by the magnetic anisotropy increases. The neutron diffraction pattern produced by such a structure exhibits a proliferation of higher order peaks (shown below) caused by both magnetic scattering and magnetostrictive deformations of the lattice.

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A semilogarithmic plot of the intensity measured on D10 with a [10l] scan, showing the main Bragg peaks (100) and (101) as well as the associated magnetic satellites.

Previous investigations of the magnetic structure of erbium have been hampered by difficulties in separating all these peaks, particularly in the 001 scan which is important in this case, since it allows the magnetic structure of the basal plane to be studied in isolation. By making full use of the high resolution available on D10 we are able to identify the majority of the higher order peaks and monitor their thermal evolution, thus allowing us to refine the "spin-slip" model of the structure. However, the most interesting information can be gained from the variation of the intensities of the higher order peaks close to the transition from a modulated antiferromagnetic to a conical ferromagnetic phase (TN = 18K). Our measurements shed new light on the magnetic behaviour as the transition is approached. Initial evaluation of the data indicates that the modulation of the c axis and basal plane moments become decoupled as the successive commensurate spiral structures are reached.

Last updated by Andrew Crowe on 05/02/1996