$A$-site-disorder-dependent percolative transport and Griffiths phase in doped manganites

The influence of $A$ site disorder on the magnetic and transport properties of ${\mathrm{Pr}}_{0.6}{R}_{0.1}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ ($R=\mathrm{Tb}$, Y, Ho, and Er) polycrystalline samples is analyzed within the context of percolative transport and the existence of the Griffiths phase. The temperature dependence of the average spin moment at the hopping sites and the fraction of metallic clusters bear signatures of the onset of the Griffiths phase. Our analysis suggests that the paramagnetic phase comprises of insulating correlated spin clusters that coexist with ferromagnetic metallic clusters and paramagnetic spins. This coexistence was found to be sensitive to the $A$-site disorder.

Figure 1

Temperature variation of inverse of susceptibility for ${\mathrm{Pr}}_{0.6}{R}_{0.1}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ with $R=\mathrm{Tb}$, Y, Ho, and Er in logarithmic scale. Arrow indicates the onset of the Griffiths phase. Inset shows the magnetization taken in field cooling mode in a field of $1000\mathrm{Oe}$.

Figure 2

Resistivity versus applied field of ${\mathrm{Pr}}_{0.6}{\mathrm{Ho}}_{0.1}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ with $T_C=145\mathrm{K}$ at different temperatures. The symbols represent the data while the lines are fits to the square of the Brillouin function (for $T=300\mathrm{K}$, $250\mathrm{K}$, $200\mathrm{K}$, $180\mathrm{K}$, $170\mathrm{K}$) and to the Brillouin function (for $T=120\mathrm{K}$ and $50\mathrm{K}$).

Figure 3

Temperature dependence of $K$ and $(1∕\chi )$ (logarithmic scale) for the investigated samples. The downward arrows mark the Griffiths temperature $T_G$, whereas the upward arrows point to $T_C$.

Figure 4

Zero field resistivity versus temperature curves plots for ${\mathrm{Pr}}_{0.6}{R}_{0.1}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ with $R=\mathrm{Tb}$, Y, Ho, and Er. The symbols represent the data while the lines represent fits to the percolation model.

Figure 5

Temperature dependence of the inverse of susceptibility (symbols) and the temperature derivative of metallic volume fraction $p$ (solid lines). Upward arrow points to $T_C$ and the downward arrow to $T_G$.

Figure 6

Temperature dependence of the inverse of susceptibility (symbols) in logarithmic scale and the temperature derivative of metallic volume fraction $p$ (solid lines) and $k$ for the PHSMO sample. Upward arrow points to $T_C$ and the downward arrow to $T_G$. The dotted line is a guide to the eye.