Ab initio study of the role of defects on the magnetic response and the structural, electronic and hyperfine properties of ZnFe 2 O 4 . `

Defective zinc ferrites ZnFe 2 O 4-δ obtained by vacuum annealing bulk Zn-ferrite at different temperatures T Ann were investigated by using XANES at Zn-K, Fe-K and XMCD at Fe-L 2,3 edges, static and dynamic magnetic measurements. The cation inversion that confers to the starting ferrite a weak ferromagnetic response is progressively lost when T Ann surpasses 250 ºC. Consequently, there is a detriment of the magnetic response that reaches its lower value for T Ann around 370 ºC, being the latter coincident with a negligible non-equilibrium occupancy. Above T Ann ∼ 450 ºC the ferrite progressively enhances its magnetic response. In such case, even though Zn and Fe occupy non-equilibrium sites at surface regions, the deficiency of oxygen predominates over inversion and the former triggers an increment of the magnetic coupling between Fe 3+ at octahedral spinel sites. We discuss the magnetic results that account for spin-glass and/or cluster-glass behavior of this geometrically frustrated compound as due to the randomness and frustration introduced by local defects.