Canted spin structures

Defects in ferrimagnetic structures often lead to noncollinear (canted) spin structures. For example, a diamagnetic substitution or a cation vacancy can result in magnetic frustration which leads to spin-canting such that a spin may form an angle 6c with the collinear spins in the sample [80, 81]. Similarly, the reduced number of neighbor ions at the surface can also lead to spin-canting [80-83]. 

Neutron-scattering experiments by Vasiliu-Doloc et al. (1998a) on an x = 0.15 sample showed the ferromagnetic order below 7c = 235 K developed a canted-spin structure below... 

Antiferromagnetic sheets, but coupling between sheets gives noncollinear, canted spin structure. The two spin directions alternate in successive sheets along the c axis. Spin vectors lie in y-z plane at alternately clockwise and counterclockwise angles of 25 =fc 2° from the b axis. 

A canted spin structure may exist under certain conditions, see pp. 191, 206, and 217. Regarding the ferromagnetic phase, see the following section. 

Tc increases from 6.4 K at 14 kbar through 8.3 K at 20 kbar (range of suggested canted spin structure) to 13.2 K at 37 kbar. The increase of Tc has been correlated with a strong increase in the magnitude of the transferred hyperfine fields, Moser etal. [33]. 

Spin-only moments would give /z = l/z5 and 0hb, respectively. Since the spins are in the (111) plane (303), a contribution to the ferrimagnetic moment should come from a canted-spin configuration. Orbital contributions to the g factor must also be playing a role, especially in the case of Co2+. It was pointed out in the discussion on rock salt structures that Co2+ in CoO carries an atomic moment of 3.7hb rather than the spin-only value of 3.0/z, and that this moment can be accounted for quantitatively if orbital considerations are included. 

Figure 7.16 Canted spin moments in TbCoO and DyCoO (a) structure projected down (001) (b and d) canted spin orientation on Tb at z=V4, % (c and e) canted spin orientation ion at z= A, (Data from Knizek et al. (2014))...

If the canting is not the same for each magnetic cation but varies in a regular way, then a number of commensurate or incommensurate spin structures can arise, including helical, helicoidal, cycloidal and sinusoidal. The helicoidal and sinusoidal ordering patterns are illustrated by the magnetic structure of TbMnOj (Section 7.10). 

The Mn-Mn separation in DyMn2 is exactly at its critical value. In consequence, it was shown by neutron diffraction (Ritter et al. 1991) that below the Curie temperature of Jc=45K only one out of four (of the crystallographic equivalent) Mn atoms possess a magnetic moment (fiua = 1-4/4b). These spins are ferromagnetically ordered. The Dy sublattice forms a spin-canted FM structure with /toy = 8.8/tB. The Mn atoms that... 

The muon senses small variations (i.e., minor spin canting) even in otherwise well-established spin structures. It is mandatory that the pSR magnetic parameters and their temperature and/or pressure dependences be consistent with the findings of other methods, in particular with neutron scattering data. This task is far flrom completed in a number of systems studied thus far, and the pSR results indicate in these cases that the magnetic structure is not understood in all details. 

Submonolayer coverages of H on Gd, chemisorbed at 20 K, drastically reduce the spin polarization of photoelectrons, because of the formation of a canted or disordered spin structure at the Gd surface with a lower ordering temperature (Cerri et al, 1983),... 

---