Anomalous ferromagnetism in manganites by finite block spin phenomenology

We investigate the relation between ferromagnetism and spin glasses which have been observed in manganese oxides.We want to explain the spin-glass phase on the basis of finite-sized block spin concepts.Then the phase of colossal ferromagnetism in manganites may be considered as the ferromagnetic ordering between block spins comprised of many random spins with respective majority spin directions. Using the Curie law for block spins, the magnetization and susceptibility are obtained in the lower-temperature and higher-temperature approximations of Brillouin function. The resistivity is also obtained from the electric susceptibility.