Selective substitution in orbital domains of a low doped manganite : an   investigation from Griffiths phenomenon and modification of glassy features
  An effort is made to study the contrast in magnetic behavior resulting from minimal disorder introduced by substitution of 2.5% Ga or Al in Mn-site of La${_{0.9}}$Sr$_{0.1}$MnO${_3}$. It is considered that Ga or Al selectively creates disorder within the orbital domains or on its walls, causing enhancement of Griffiths phase (GP) singularity for the former and disappearance of it in the later case. It is shown that Ga replaces Mn$^{3+}$ which is considered to be concentrated within the domains, whereas Al replaces Mn$^{4+}$ which is segregated on the hole-rich walls, without causing any significant effect on structure or ferromagnetic transition temperatures. Thus, it is presumed that the effect of disorder created by Ga extend across the bulk of the domain having correlation over similar length-scale resulting in enhancement of GP phenomenon. On the contrary, effect of disorder created by Al remains restricted to the walls resulting in the modification of the dynamics arising from the domain walls and suppresses the GP. Moreover contrasting features are observed in the low temperature region of the compounds; a re-entrant spin glass like behavior is observed in the Ga doped sample, while the observed characteristics for the Al doped sample is ascribed only to modified domain wall dynamics with the absence of any glassy phase. Distinctive features in third order susceptibility measurements reveals that the magnetic ground state of the entire series comprises of orbital domain states. These observations bring out the role of the nature of disorder on GP phenomenon and also reconfirms the character of self-organization in low-doped manganites. 
K. Mukherjee and A. Banerjee