Magnetic Properties of Ultrathin Magnetite Films Grown by Molecular Beam Epitaxy

Abstract

Magnetic properties as a function of film thickness (2-55 nm) for magnetite (Fe 3 O 4 ) thin films grown on MgO (100) substrates show that the small thickness films ( 5 nm) are ferromagnetic and possess magnetization values which are much greater than that of bulk Fe 3 O 4 . The inverse thickness dependence of the magnetization points to an interface related mechanism. Whereas, our detailed spin polarized density functional theoretical calculations suggests that there is only a marginal enhancement in the local spin moments of Fe-atom in the vicinity of the Fe 3 O 4 -MgO interface and it turns out that the noncompensation of spin moments between the two magnetic sublattices of spinel Fe 3 O 4 is a major factor contributing to the enhancement of magnetization.

Origin of the giant magnetic moment in epitaxialFe3O4thin films

“…͑2͒, as suggested by Arora et al, 26,27 obtaining a bulk saturation magnetization M S = 349Ϯ 41 emu/ cm 3 and a surface contribution M i = 2088Ϯ 274 emu/ cm 3 , in agreement with. 26,27 The presence of the Verwey transition down to 4-nm-thick films ͑Fig. 3͒ evidences the high quality of the films.…”

“…However, recent x-ray magnetic circular dichroism ͑XMCD͒ and resonant photoemission experiments have ruled out this hypothesis. 29 We have obtained similar magnetization results to those reported by Arora,26,27 therefore, the purpose of the present work is to investigate further the origin of the anomalous giant magnetic moment in epitaxial Fe 3 O 4 thin films grown on MgO ͑001͒. In Sec.…”

“…However, recent studies performed by Arora et al 26,27 on well-characterized epitaxial Fe 3 O 4 thin films grown on MgO ͑001͒ show that the ultrathin films ͑Ͻ5 nm thickness͒ are ferromagnetic and their magnetization is much greater than that of bulk magnetite. The main factor contributing to the observed enhanced magnetic moment is proposed to be the noncompensation of spin moments between the tetrahedral and octahedral sublattices at the surface, at the interface with the substrate, and at the antiphase-domain boundaries.…”

Synthesis of phase pure iron oxide polymorphs thin films and their enhanced magnetic properties

“…As an example, Lin et al [22] has reported that the value of M s and coercivity is 305 emu/cm 3 and 400 Oe, respectively, when the Fe 3 O 4 films of thickness 150 nm was prepared by the reduction of a-Fe 2 O 3 . We know that the magnetization of a film decreases with the increasing thickness of Fe 3 O 4 [44]. In our case we observed Table 2.…”

The investigation of giant magnetic moment in ultrathin Fe3O4 films

“…The main factor contributing to the observed enhanced magnetic moment is proposed to be the noncompensation of spin moments between the tetrahedral and octahedral sublattices at the surface, interface, and across the APBs. 17,18 Another study suggested that the giant M s may come from the Fe impurities in the commercial MgO substrate. 19 These converse results make the phenomena of enhancement of M s and its mechanism in ultrathin Fe 3 O 4 film is uncertain and needs further study.…”