Magnetic relaxation phenomena and cluster glass properties of   La{0.7-x}Y{x}Ca{0.3}MnO{3} manganites
  The dynamic magnetic properties of the distorted perovskite system La{0.7-x}Y{x}Ca{0.3}MnO{3} (0 <= x <= 0.15) have been investigated by ac-susceptibility and dc magnetization measurements, with emphasis on relaxation and aging studies. They evidence for x >= 0.10 the appearance of a metallic cluster glass phase, that develops just below the ferromagnetic transition temperature. The clusters grow with decreasing temperature down to a temperature T(f0) at which they freeze due to severe intercluster frustration. The formation of these clusters is explained by the presence of yttrium induced local structural distortions that create localized spin disorder in a magnetic lattice where double-exchange ferromagnetism is dominant. 
R.S. Freitas, L. Ghivelder, F. Damay, F. Dias, and L.F. Cohen