Disorder-induced short-range ferromagnetism and cluster spin-glass state in sol-gel derivedLa0.7Ca0.3Mn1−xCdxO3(0⩽x⩽0.2)

Abstract

Low temperature magnetic and transport properties of the sol-gel derived Cd doped ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Cd}}_{x}{\mathrm{O}}_{3}(0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.20)$ manganite system show ferromagnetism and cluster spin-glass behavior. Metal-insulator transition (MIT) is exhibited only by the samples with $x\ensuremath{\leqslant}0.1$; and for higher concentrations ($x=0.15$ and 0.20), samples are semiconductors. The MIT shifts to the lower temperature regime with increasing Cd content, indicating an increase of disorder in the system. Structural analysis shows local strain-induced small lattice distortion of the $\mathrm{Mn}{\mathrm{O}}_{6}$ octahedra with Cd doping. With increasing Cd content, the system undergoes interesting paramagnetic to ferromagnetic (with $xl0.10$) as well as paramagnetic to cluster spin-glass (for $x\ensuremath{\geqslant}0.10$) transitions. ac susceptibility $({\ensuremath{\chi}}_{\mathrm{ac}})$ and magnetic relaxation measurements confirm this cluster spin-glass behavior. ${\ensuremath{\chi}}_{\mathrm{ac}}$ is found to follow the critical slowing down law $(\ensuremath{\tau}∕{\ensuremath{\tau}}_{0}={\ensuremath{\epsilon}}^{\ensuremath{-}z\ensuremath{\nu}})$. The magnetic hysteresis loops indicate a field-induced irreversible ferromagnetic phase due to the presence of ``weak'' antiferromagnetic domains in the samples with $x\ensuremath{\geqslant}0.10$. This typical behavior is found to be most prominent in the sample with $x=0.15$. The observed cluster spin-glass state is explained by considering the interactions between the ferromagnetic and antiferromagnetic clusters in these doped systems having disorder and reduced geometrical tolerance factor $t$, which resulted from the random substitution of Mn with Cd ions.