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Nanoscale Ferromagnetism in Alloy Thin Film via Lattice Disordering

Bali, R.; Schmeink, A. H.; Eggert, B.; Ehrler, J.; Liersch, V.; Semisalova, A.; Hlawacek, G.; Potzger, K.; Faßbender, J.; Thomson, T.; Wende, H.; Lindner, J.


Structural disorder in certain alloys leads to the onset of strong ferromagnetism. Disorder can be induced in desired locations, at the nanoscale, making such materials useful for magnetic nano-patterning. Examples of these alloys include Fe60Al40,[1] Fe50Rh50,[2] and Fe60V40. Disorder can be generated locally using focussed ion- as well as laser- beams,[1 - 3] inducing nanoscale ferromagnetism. Furthermore, the effect can be reversed via thermal re-ordering of the alloy, achieving re-writeable magnetic structures.
Insights into the mechanisms of the ferromagnetic onset in prototype systems, helps achieve a broader understanding of magneto-structural correlations in general. For instance, in paramagnetic B2-ordered Fe60Al40 as well as D8b-type Fe60V40, the ferromagnetic onset is caused by antisite defects i.e. site swapping of the Fe and Al (V) atoms, resulting in a transition to the bcc (A2) structure. An increase of antisite defects can cause the Ms of Fe60Al40 as well as Fe60V40 to increase from nearly-zero in the ordered structures to 780 and 660 kAm-1, in their respective disordered structures. In contrast, in B2 Fe50Rh50 the well-ordered film is antiferromagnetic, and static disordering may be sufficient to fully transform the alloy to the ferromagnetic phase, possessing an Ms of ~ 1250 kAm-1 at 300 K. Thus, whereas the Ms in the above alloys increases drastically with lattice disorder, the microscopic nature of the disordering varies.
Here we deploy ion-irradiation to sensitively induce lattice disorder in the above binary alloy systems, while tracing the manifested ferromagnetic onsets, thereby obtaining insights into the correlation between magnetic behaviour and the structure. Properties of magnetic arrays and magneto-transport devices produced using lattice disorder will be discussed.
[1] “Printing Nearly-Discrete Magnetic Patterns Using Chemical Disorder Induced Ferromagnetism”, R. Bali et al., Nano Letters 14, 435 (2014).
[2] “Tuning the antiferromagnetic to ferromagnetic phase transition in FeRh thin films by means of low-energy/low fluence ion irradiation”, A. Heidarian et al., Nucl. Instrum. Methods Phys. Res. B 358, 251 (2015).
[3] “Laser-Rewriteable Ferromagnetism at Thin-Film Surfaces”, J. Ehrler et al., ACS Appl. Mater. Interfaces 10, 15232 (2018).

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Related publications

  • Invited lecture (Conferences)
    6th International Conference from Nanoparticles and Nanomaterials to Nanodevices and Nanosystems (6th IC4N), 30.06.-03.07.2019, Corfu, Greece
  • Invited lecture (Conferences)
    Symposium „Spins, Waves and Interactions“, 03.-05.09.2019, Greifswald, Deutschland


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