1. The $$\left[ {\bar 110} \right]$$ direction is an easy axis too. The direction $$\left[ {\bar 110} \right]$$ is equivalent to the direction [110] in the context of our study.
2. “T N” is used in order to distinguish it from the Néel temperatureT N defining the sharp phase transition of the system.
3. As we mentioned in sect. 3, the oblique spin direction was not detected definitely in K2Ni1−x Fe x F4. Therefore, there remains a possibility that the widths of both OAF phases in fig. 6 collapse into zero. If the present system is such, the transition between the regions [001] and [100], and that between the regions [100] and [110] should be of first-order; however, we have to mention that any hysteresis has not been observed around either of the transition temperaturesT θ andT ϕ.
4. See a review by A. Ito, in:Proc. Int. Conf. on the Applications of the Mössbauer Effect, Hyp. Int. 27–29 (1986) 81.
5. A. Aharony and S. Fishman, Phys. Rev. Lett. 37 (1976) 1587; S. Fishman and A. Aharony, Phys. Rev. B 18 (1978) 3507.