Spin-slip structure

While a number of other lanthanide systems have been prepared as multilayers, few have been examined systematically as epitaxial films. The Oxford group, Jehan et al. (1993), report that 5000 A of Ho on Y exhibits clearer spin-slip structures than the bulk. They also report that Tn is depressed by 1 K, and the low-temperature c /6 phase is absent. 

Erbium exhibits a complex magnetic behaviour, with at least four obserrable characteristic temperatures below rN = 85K, the moments order in a sinusoidal c-axis modulated (CAM) structure at rH=54K, there appears a component perpendicular to the c-axis resulting in a helicoidal structure this intermediate phase exhibits a sequence of lock-in transitions of commensurate phases (spin-slip structures) with wave vectors fm = f, 4 observed by iX-ray scattering (Gibbs et al. 1986), the... 

Fig. 127. Self-consistent mean-field calculations of periodic stmctuies in Ho. Each circle represents the magnitude and direction of the ordered moment in a specific plane, relative to the size of the moment at absolute zero (lO/tg), indicated by the length of the horizontal lines. The orientation of moments in adjacent planes is depicted by the positions of the neighbouring circles, (a) The 12-layer zero-spin-slip structure at 4K. The open circle in the centre indicates the ferromagnetic component in the cone structure (b) the 11-layer one-spin-slip structure at 25 K. The bunched pairs of moments are disposed asymmetrically with respect to the easy axis in the vicinity of the spin slip (after Jensen and Mackintosh 1992).

Fig. 7. Temperature dependence of the modulation wave vector for three different Ho samples Ho(l) (crosses), Ho(2) (open circles), and thin film (solid circles). The spin-slip structure for the simply commensurate wave vectors are shown on the right. The data for r = j in Ho(l) were obtained from neutron scattering. Note also the appearance of two new lock-in wave vectors at j and (From Gibbs 1989.)...

As has been outlined in previous sections. Ho and Er each exhibit spin-slip structures at low temperatures, and the expectation is that alloys of these two elements should also display some interesting and related features. Indeed a neutron scattering study of a Hoo.5Ero,5 alloy by Howard and Bohr (1991) revealed tinee distinct temperature intervals. (1)47.5K 104K. The alloy orders at a temperature close to the weighted average... 

Bates et al. (1988) explained the appearance of the anomalies at c,y by a change of the effective magnetic symmetry caused by supercommensurate spin-slip structures which break the underlying hexagonal crystal symmetry. The anomalous elastic constant change at the spin-slip transition was expressed as... 

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