X-ray Critical Scattering in NiCr₂O₄

Abstract

The X-ray critical scattering in NiCr₂O₄ in the vicinity of its Jahn-Teller phase transition has been investigated in order to clarify the nature of the interaction between local distortions. The results are summarized as follows:
(i) The critical scattering due to correlation of local distortions has been observed up to 100 K above the transition temperature.
(ii) Relative intensities of the critical scattering around various reciprocal lattice points confirm that the correlation of local distortions propagates through acoustic type displacement field, showing that the indirect pair interaction via strain field is dominant to cause Jahn-Teller phase transition in NiCr₂O₄.
(iii) The characteristics of the anisotropy of the critical scattering show a singularity at k=0, indicating that the interaction is of long range.
The above results are in very good agreement with the theory recently developed by Kataoka and Kanamori.