Abstract
We observe exchange bias (EB) in a single magnetic film Fe3O4 at temperature T < 200 K. Irrespective of crystallographic orientations of grown Fe3O4; they exhibit similar nature of EB for (100) epitaxial, (111) oriented and polycrystalline Fe3O4 thin films. Growth induced defects such as anti-phase boundaries (APBs) in epitaxial Fe3O4 thin film is known to have an influence on the magnetic interaction. But, it is noticed that according to the common consensus of APBs alone cannot explain the origin of EB. If majority of APBs end up with mainly anti-ferromagnetic interactions across these boundaries together with the internal ordering modification in Fe3O4, then EB can emerge at low temperatures. Hence, we propose the idea of directional anti-ferromagnetic APB induced EB in Fe3O4 triggered by internal ordering for T ≤ 200 K. Similar arguments are extended to (111) oriented as well as polycrystalline Fe3O4 films where the grain boundaries can impart same consequence as that of APBs.
Highlights
Exchange bias (EB) is an effect observed when a ferromagnetic (FM) material is in the proximity of anti-ferromagnetic (AFM) material.[1]
It is interesting to see that the growth of Fe3O4 thin film on majority of substrates lead to structural defects known as anti-phase boundaries (APB).[12,13,14,15,16,17,18,19,20]
It is known that if there is a deviation in the stoichiometry of Fe3O4, the Tv will shift to lower values as well as result in broader transition in single crystalline Fe3−δO4 for δ > 0.26,28 In case of thin films, occurrences of APBs are adding to the deviation of stoichiometry
Summary
Exchange bias (EB) is an effect observed when a ferromagnetic (FM) material is in the proximity of anti-ferromagnetic (AFM) material.[1]. Liu et al.[8] suggest that the occurrence of APBs could lead to the EB effect in Fe3O4 films grown on α-Al2O3(0001). In both the cases,[8,10] EB effect is seen only at temperatures T < 200 K. We have tried to address the nature and origin of the EB and how APBs or grain boundaries could influence the EB in (1) epitaxial Fe3O4 film on MgO/GaAs (2) grain boundary influenced EB in oriented Fe3O4 film on GaAs and (3) polycrystalline Fe3O4 on MgO/Si. We observe a direction dependent modulation of EB in different samples of Fe3O4
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