A study of the effect of iron island morphology and interface oxidation on the magnetic hysteresis of Fe-MgO (001) thin film composites

Abstract

Fe-MgO tunnel junctions have received much attention for their use in hard drive read heads and other spintronic applications. The system is particularly interesting because of its magnetoresistive behavior and the abundance and low cost of its constituent elements. However, many questions remain about how the structure and chemistry of the Fe-MgO interface mediates magnetic behavior. In this study, we report on transmission electron microscopy, electron energy loss spectroscopy, and magnetic characterization of Fe-MgO composite films with various morphologies. We explore relationships between film morphology, intermixing, and the resulting effects on magnetic structure. We find the presence of oxidation at the Fe-MgO interface, with a detrimental impact on the saturation magnetization of the composite. We also observe changes in coercivity and magnetocrystalline anisotropy with film morphology and thickness. These results will inform the design of MgO-based tunnel junctions and improve our understanding of how processing conditions, resulting in morphological and chemical changes such as oxidation, affect magnetization.

Effect of capping material on interfacial ferromagnetism in FeRh thin films

“…Near the substrate, we speculate that this variation in the FeRh composition with depth is due to Fe deficiency because of Fe diffusion into the MgO substrate. Interfacial diffusion between Fe and MgO has been reported in studies related to magnetic tunnel junctions with formation of an inter-diffused (Mg,Fe)O layer at the interface after annealing to temperatures above 450 C. 33,34 Our films are deposited at 600 C and a similar effect would result in Fe depletion in the bottom layer, therefore increasing the Rh concentration locally. As discussed in the introduction, an increase in Rh concentration lowers T 0 and can lead to the stabilization of the FM phase at RT.…”

Magnetic properties of the Fe-MgO interface studied by Mössbauer spectroscopy

“…[1][2][3] The theoretically predicted 4 lack of electronic interaction between Fe and MgO and the calculated giant Fe monolayer magnetization inspired many experimental works on the magnetic properties of Fe thin films over MgO substrates. [5][6][7][8][9][10][11] Also a large number of works has been devoted to Fe/MgO multilayered structures. [12][13][14][15][16] In agreement with an early paper, 4 recent ab initio spin-density-functional calculations 17 indicated an increased magnetic moment (2.94μ B ) at the (001) surface of the bcc-Fe layer and pointed to the role of in-plane tensile strains in a further increase of it.…”

Reactive metal–oxide interfaces: A microscopic view

“…An even richer phenomenology and somehow controversial results can be found in the case of interfaces formed between MgO and Fe(001). While most of the experimental works report on the formation of an atomically sharp Fe/MgO interface [50][51][52], in line with the lower heat of formation of MgO with respect to that of Fe oxides (see Table 1), in some cases the presence of Fe oxide at the Fe/MgO interface has been reported [53,54]. Concerning the MgO/Fe interface, high quality MgO films can be obtained by direct evaporation of stoichiometric MgO [55,56], a procedure that allows avoiding the strong Fe oxidation induced by the oxygen atmosphere employed during reactive deposition [57].…”