Low-temperature thermodynamics of magnetically ordered states of a narrow-band Habbard magnetic material

The effects of exchange and doping degree in the ground state structure of a narrow-band Habbard magnetic material are investigated in the framework of a t-J-model. The boundaries of ferro-, antiferro- and paramagnetic phases are determined. The low-temperature thermodynamics of a ferromagnetic state is studied. It is found that at temperature T/W << 1 (W is the band width) a concentration decrease in magnetization exists down to zero which is due to the influence of thermal fluctuations on the saturated ferromagnetic state. The experimentally observed peculiarities of the susceptibility behavior such as the paramagnetic increase ∼ 1/T and the occurrence of a Shottky-type maximum are qualitatively treated