Linear antiferrodistortive-antiferromagnetic effect in multiferroics: Physical manifestations

摘要: Using the theory of symmetry and microscopic model we predict possibility a linear antiferrodistortive-antiferromagnetic effect in perovskites with structural antiferrodistortive antiferromagnetic long-range ordering find necessary conditions its occurrence. The main physical manifestations this are smearing transition jump specific heat near it. In absence external fields, coupling can induce weak above Neel temperature, but below temperature transition. Therefore, there is observing improper antiferromagnetism multiferroics such as bismuth ferrite ($\mathrm{BiFe}{\mathrm{O}}_{3}$) at temperatures $Tg{T}_{N}$, for which ${T}_{N}$ about 645 K, 1200 K. mechanism may explain order existence well ${\mathrm{BiFeO}}_{3}$ revealed by optical second harmonic generation. By quantitative comparison to experiment made estimations solid solutions multiferroic $\mathrm{B}{\mathrm{i}}_{1\ensuremath{-}\mathrm{x}}{\mathrm{R}}_{\mathrm{x}}\mathrm{Fe}{\mathrm{O}}_{3}$ ($\mathrm{R}=\mathrm{La},\phantom{\rule{0.28em}{0ex}}\mathrm{Nd}$).