C-axis modulated

Fig. 11. Orthorhombic distortion of tetragonal HoNi2B2C (a) upon cooling from 15 K to 1.5 K the neutron diffraction reflection (332) splits into two peaks, (b) Schematic presentation of the distortion a,b — original tetragonal axes dashed line tetragonal basal plane —f shift of the Ho atoms leading to the orthorhombic cell with the axes onh- Thick arrows Ho magnetic moments in the commensurate c-axis modulated structure...

Er 9 32 80 c-Axis ferrimagnetic cone structure c-Axis modulated structure... 

Fig. 2. Schematic description of the spin structures in the heavy rare earth metals. The initial high-T ordering, in all except the ferromagnet Gd, is to an incommensurate periodic spin order with propagation direction along the c-axis. CAM (c-axis modulation) is a structure in which the c-axis components of the moment are sinusoidally modulated which evolves into the APD (quasi anti-phase domain) in Er in which a gradual squaring-up of the c-axis moment occurs with additional order appearing in the basal plane. The temperatures of the transitions are from magnetization and neutron diffraction data. (After Legvold 1980.)...

The complexity of the Er magnetization process is again illustrated by the data of Feron et al. (1970), extending up to Tni (hg. 6.10). The critical held along [0001] required to decouple the c-axis modulated moments (above Tc) increases... 

Magnetostrictive effects in Er are clearly visible in the temperature variation of the lattice parameters determined in the neutron diffraction study of Haben-schuss et al. (1974). The appearance of the c-axis modulated structure below Tv = 84.4 K has little effect on the lattice constants (fig. 6.35), but below the basal plane ordering temperature Ts 52.4 K, the c-axis expands in the manner of the exchange magnetostriction found in the spiral phases of Tb and Dy. Ferromagnetic alignment of the c-axis moment at Tc = 18 K is marked by a... 

The c-axis modulation due to the bilayer coupling which leads to an optic and acoustic mode in the spin-wave cross-section for antiferromagnetically ordered samples is also... 

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... 

Allowed and forbidden E and E2 transitions at die L and Lm edges in a pure c-axis modulated stmeture. A 1 indicates that the transition is allowed and 0 that it is forbidden... 

Fig. 25. Combined X-ray (solid circles) and neutron (open circles) scattering results from Er for the fundamental wave vector and for the additional scattering from lattice modulations at 2t , and 2r - %. The peak observed at r in the c-axis modulated phase above 52 K is the principle magnetic satellite of the (110) reflection, obtained by neutron scattering. All remaining data are satellites of the Bragg (002) and (004) reflections. The X-ray results at 2t - were partially obscured by higher-order contamination. (From Gibbs et al. 1986.)...

One other notable feature of the data shown in fig. 25 is that in the non-resonant scattering experiments no scattering was observed at the primary satellite position tm in the purely c-axis modulated phase that exists above 52 K, where the cross-section varies as sin 6 and is weak. This observation had to wait for resonant scattering techniques to be applied to the problem. 

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