Collinear spin structure

Most importantly, however, the results summarized in Table 5.4 are in full agreement with a criterion formulated by Sandratskii and Kttbler for the instability of a collinear spin structure ... 

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]. 

Assumes collinear spins. Multiple-axis structures may also be possible. 

As mentioned earlier, the linear exchange interaction between Cu layers cancels due to the bet symmetry, and the actual spin structure is then a result of a delicate balance of superexchange, spin-orbit, and Coulomb exchange interactions (Yildirim et al. 1994, 1996). In the absence of the R ions, quantum fluctuations would be expected to yield the collinear magnetic structure (Yildirim 1999) and this may indeed be the case for the Sr2Cu02Cl2 material (Yildirim et al. 1998). However, this leaves unexplained the... 

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