Mössbauer spectroscopy of ${\mathrm{La}}_{0.7-x}{\mathrm{Dy}}_x{\mathrm{Ca}}_{0.3}\mathrm{Mn}\left(\mathrm{Fe}\right){\mathrm{O}}_3$ shows phase separation, both above and below $T_C$. The behavior in the two regions are independent and related to different phenomena. Above $T_C$, the phase splitting is due to different lattice distortions. In one of the phases, Jahn-Teller distortion is significant. Below $T_C$, the spin orderings in the two phases are ferromagnetic (FM) and spin glass (SG) orderings, respectively. At low temperatures, SG phase converts into FM phase when the applied magnetic field increases, but only partially. We find a drastic increase in magnetoresistivity (MR) as $x$ is increased beyond 0.07. It attains a maximum value for $x\approx 0.12$ (greater than 750 000%) and decreases again rapidly as $x$ increases. We have provided an explanation for the high MR in $x=0.12$ phase. Other differences between the compositions studied here can also be identified. First, the phase with Jahn-Teller distortion disappears when the temperature is lowered to $T_C$ in a composition with $x⩾0.12$. This is not the case when $x=0.07$. Second, we observe anomalous hysteresis loop when $x=0.12$. The anomaly is less pronounced in other compositions. Third, in composition $x=0.07$, the hyperfine magnetic fields $\left(H_{\mathrm{int}}\right)$ in FM and SG components are distinctly different. This is not so when $x=0.12$.

• Received 7 April 2004

DOI:https://doi.org/10.1103/PhysRevB.71.104419