Local states of iron ions in multiferroics Bi$_{1-x}$La$_x$FeO$_3$

Mössbauer studies of perovskites Bi$_{1-x}$La$_x$FeO$_3$ ($x$ = 0, 0.10, 0.20, 0.61, 0.90, 1.00) were conducted at 295 and 87 K. The spatial spin-modulated structure (SSMS) observed in perovskites BiFeO$_3$ and Bi$_{0.9}$La$_{0.1}$FeO$_3$ leads to a specific distribution of hyperfine fields $P(B)$ with two peaks. Substitution of La for Bi ($x$ = 0.2) destructs the SSMS. The concentration dependences of the hyperfine field $(B)$, isomer shift $(\varepsilon)$ and quadrupole shift $(\delta)$ were measured. The iron ions are in the trivalent state. The local magnetic moments $\mu$(Fe) of the Fe$^{3+}$ ions are determined.