Correlating exchange bias with magnetic anisotropy in ion-beam bombarded NiFe/Mn-oxide bilayers

Abstract

The exchange bias field dependence on the Mn-oxide and its microstructure in NiFe/Mn-oxide bilayers was investigated. Transmission electron microscopy results have shown that the bilayer bottom consisted of either alpha-Mn, rocksalt MnO, or a composite of tetragonal Mn(3)O(4)+MnO, depending on the ratio of O(2)/Ar used during dual ion-beam deposition. Magnetometry results at 5 K indicate that the exchange bias field (H(ex)similar to-300 Oe) is largest in a NiFe/Mn (0%O(2)/Ar) bilayer. The MnO formation by in situ Mn oxidation results in a decrease in H(ex) in a NiFe/Mn-oxide (21%O(2)/Ar) bilayer. In contrast, a further increase in the O(2)/Ar ratio during deposition results in larger H(ex) and H(c). This is attributed to the oxidation of MnO into a harder ferrimagnet, Mn(3)O(4). Our results indicate that the antiferromagnetic Mn enabled stronger coupling with NiFe than MnO. In addition, we find that the MnO-Mn(3)O(4) coupling dominates the exchange bias effects at high oxygen concentrations

Exchange bias effect involved with tunneling magnetoresistance in polycrystalline La0.88Sr0.12CoO3

“…The simple intuitive model [29] as well as sophisticated theories [30,31] seem to agree that the exchange bias effect should be larger for larger anisotropy of the AFM substance in a FM/AFM heterostructure which has been elaborately described by Nogués et al [3]. Although the experimental investigations [32][33][34] dealing with the role of the anisotropy seem to agree with the theories, any quantitative conclusions from them could not be established because of the difficulties for extracting the anisotropy of the AFM component from the heterostructure. In the present observation the larger EB field is found to be associated with the larger coercivity obtained from the MR-H curve which is in accordance with the proposed theories [29][30][31] as well as the experimental results [32][33][34].…”

Correlating antiferromagnetic spin structures with ion-beam bombardment in exchange-biased NiFe/Mn bilayers

“…1͑e͔͒ with a roughness of less than 2 nm was observed, similar to that of the unbombarded Mn layer. 6 This suggests strongly that possible roughness effects 1 influencing the exchange bias behavior can be excluded since all samples exhibit the same degree of surface interfacial roughness. Therefore, only variations in spin orientations modified by the Ar ion-beam bombardment can be responsible for the variations in exchange bias behavior in the film systems.…”

“…The NiFe/Mn bilayer with the dimension of 120ϫ 120ϫ 12 nm 3 ͑40ϫ 40ϫ 6 cell 3 ͒ was used. The spin structures near the interface between NiFe and Mn can be obtained by applying the anisotropy energies ͑K͒ and exchange stiffness constants ͑Aij͒ of NiFe and Mn, 6 respectively. The preliminary results have shown that in the unbombarded Mn layer ͑V EH =0 V͒, compensated AF Mn spins aligned parallel to the interface was observed ͑left panel, the inset of Fig.…”

Exchange bias effect involved with tunneling magnetoresistance in polycrystalline La_{0.88}Sr_{0.12}CoO_3

“…Although the experimental investigations [32][33][34] dealing with the role of the anisotropy seem to agree with the theories, any quantitative conclusions from them could not be established because of the difficulties for extracting the anisotropy of the AFM component from the heterostructure. In the present observation the larger EB field is found to be associated with the larger coercivity obtained from the MR-H curve which is in accordance with the proposed theories [29][30][31] as well as the experimental results [32][33][34]. Until now, different aspects of EB effect has been extensively investigated through the magnetization studies which is rather less focused in the MR measurement.…”