Mössbauer studies of multiferroics BiFe$_{1-x}$Cr$_{x}$O$_{3}$ ($x$ = 0–0.20)

The Mössbauer studies on $^{57}$Fe nuclei in multiferroics BiFe$_{1-x}$Cr$_{x}$O$_{3}$ ($x$ = 0.05, 0.10, and 0.20) have been performed at room temperature. The multiferroics BiFe$_{1-x}$Cr$_{x}$O$_{3}$ ($x$ = 0.05, 0.10, and 0.20) with the rhombohedral $R$3$c$ structure have been prepared by solid-state synthesis under high pressures. The effect of substitution of Cr cations for Fe cations on the spatial spin-modulated structure, and also hyperfine electrical and magnetic interactions of $^{57}$Fe nuclei has been studied. The substituted ferrites demonstrate an anharmonic modulated spin structure of cycloid type, in which iron atoms with different cation environments take part. The anharmonism parameter of the cycloid linearly increases from $m$ = 0.10 at $x$ = 0 to $m$ = 0.78 $\pm$ 0.02 at $x$ = 0.20. The constants of magnetic uniaxial anisotropy K u are estimated at room temperature: $K_{u}\approx$ 0.36 $\times$ 10$^{6}$ erg/cm$^{3}$ at $x$ = 0 and $K_{u}\approx$ 4.22 $\times$ 10$^{6}$ erg/cm$^{3}$ at $x$ = 0.20.