Cluster glass behaviour in Co-substituted double perovskite Ca2FeMoO6

The transport and magnetic properties of the double perovskite compounds Ca2Fe1−xCoxMoO6 (0.1 ≤ x ≤ 0.4) have been explored through resistivity [ρ(T)], dc magnetisation [M(H, T)] and ac susceptibility [χ(T, f)] measurements. Introduction of Co increases the lattice volume implying the divalent nature of cobalt in this system. For all the samples, ρ(T) behaviour over the temperature range (25–273 K) can be adequately described by considering possible disorder-enhanced electron–electron interaction effect as well as spin-wave contribution. Our results reveal that with the increase of Co concentration, the ferromagnetic Curie temperatures (TC) gradually reduced due to the incorporation of antiferromagnetic Co2+–Mo6+ pairs replacing ferromagnetic Fe3+–Mo5+ pairs. A cluster-glass like behaviour is also observed in the system due to the presence of highly spin-disordered regions.