Spin-slip transition

Erbium. The easy direction in Er is the c-axis, and below the second-order Neel transition (Tn = 85 K), the moments order in a longitudinal sine-wave structure. As the temperature is lowered the sine squares up. Aroimd Tb = 52 K, a basal plane component begins to order, leading to a helical AFM structure. Finally, at 7c = 20K a first-order transition into a steep cone (opening angle 30 ) FM spin structure takes place. Several (first-order) spin-slip transitions occur in the helical AFM phase. 

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... 

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. 81. Low-fleld magnetization process along the [100] axis at 1.5 K in hexagonal PrGa the first transition at 2.3 kOe (increasing field) is of spin-flip type, the other ones of spin-slip type the propagation vector is C = (, 0) in...

The concept of spin-slips or discommensurations was first introduced to explain the observed lock-in transitions in the magnetic spirals of lanthanide metals such pure Ho and Dy in terms of simple commensurate structures (fig. 127). More generally this term can be used to characterize structures which present periodic faults in a simple sequence of magnetic moments. For instance, let us consider, in an Ising chain, a sequence of 4 moments up followed by 3 moments down (this is found in some compounds). The propagation vector is In certain r ons of H-T space the propagation vector is slightly... 

In the same figure the derivative of the resistivity is also plotted, where many anomalies (indicated by arrows) related to transitions between spin-slip phases are apparent. 

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