Magnetic properties of nanosized Sr_2CrReO_6 powders prepared by a combustion synthesis process

摘要

Double perovskite, Sr_2CrReO_6, nanoparticles in the size range 10-25 run have been prepared by a combustion method. Its coercivity (H_c) at 5 and 300 K are determined to be 16.1 and 6.5 kOe, respectively. Using the law of approach to saturation, the obtained saturation magnetization sigma_s (5 K) and sigma_s (300 K) are 0.41 and 0.32 mu B per formula unit (f.u.), respectively. The values of saturation magnetization are lower than the expected value 1 mu B/f.u. considering the antiferromagnetic coupling between Cr~(3+) (3d~3, S=3/2) and Re~(5+) (5d~2, S=1). At the same time high field irreversibility in M(H) curves and zero field cooled-field cooled (ZFC-FC) processes has also been found. A field-cooled (FC) hysteresis loop shift decreases with increasing temperature and vanishes near 350 K. It is suggested that the observed reduction of sigma_s and shifted hysteresis loops are caused by the exchange interaction between the ferromagnetic core of the Sr_2CrReO_6 nanoparticles and its surface layer with disordered spins.