Negative spontaneous magnetization and semi-spin glass magnetic order in mixed spinel Co0.6Zn0.4Fe1.7Mn0.3O4.

In this paper, we establish the negative spontaneous magnetization in Mn and Zn substituted cobalt ferrite Co_0.6Zn_0.4Fe_1.7Mn_0.3O₄ (CZFMO). It is suggested that the origin of negative spontaneous magnetization is due to the substitution of small sized Mn⁺⁴ ions (compared to Fe⁺³ ions) at the octahedral B site in compound Co_0.6Zn_0.4 Fe₂O₄. The low value of Poisson's ratio ~0.202 for this compound possibly contributes towards the easy distortion in the bond length and bond angle, causing increase in Fe-O bond distance/decrease in Fe-O-Fe bond angle with Mn substitution, leading to considerably weak Fe-O-Fe superexchange interaction at the octahedral B site. The neutron diffraction data clearly illustrated the significant reduction in ordered magnetic moment at the B site, with the resultant negative spontaneous magnetization (M=M_B-M_A) in this mixed spinel system. The spin disorder also gives rise to an interesting semi-spin glass behavior in CZFMO. [ABSTRACT FROM AUTHOR]