Memory effects and magnetic relaxation in single-crystalline   La$_{0.9}$Sr$_{0.1}$CoO$_3$
  We report a detailed investigation of magnetic relaxation and memory effects in La$_{0.9}$Sr$_{0.1}$CoO$_3$ single crystal from dc magnetization measurements. The analysis of magnetic relaxation at different temperatures and magnetic fields below the freezing temperature ($T_{f}$) manifests the characteristics of spin glass phase. Below $T_{f}$, striking memory effects have been clearly observed in different experimental protocols. The memory effect in the zero-field-cooled magnetization further establishes that the glassy magnetic state arises from the co-operative spin-spin interaction but not due to the independent relaxation of metastable phase clusters. The asymmetric response with respect to negative and positive temperature change favors the hierarchical model of memory effects rather than the droplet model discussed in other works for different insulating and metallic Heisenberg spin glasses. 
N. Khan, P. Mandal, and D. Prabhakaran
cond-mat.str-el