Neutron diffraction study of magnetic ordering in the spinel oxide CoxMn1−xAl2xFe2−2xO4

Abstract

Four samples of the mixed spinel system Co x Mn 1− x Al 2 x Fe 2−2 x O 4 ( x =0.2, 0.4, 0.6, 0.8) were synthesized by ceramic sintering method. The magnetic ordering in the system has been investigated by neutron diffraction measurements in the temperature range 15–773 K. It appears that the system possesses a long-range ferrimagnetic ordering at x ≤0.6 along with some randomly canted spin components, while at x =0.8 a semi-spin glass behavior is observed. The latter composition exhibits three transitions: at temperatures larger than 100 K, there is formation of magnetic spin clusters showing super-paramagnetic type behavior before the true paramagnetic region is reached at about 200 K; a ferrimagnetic long-range ordering is observed in the temperature range 100–50 K; and finally below 50 K there is freezing of the magnetic spin clusters.