Anisotropy engineering of soft thin films in the undulated magnetic state

• Published in: Journal of magnetism and magnetic materials 2020-11, Vol.514, p.167149, Article 167149
• Main Authors: Sánchez, Elena H., Rodriguez-Rodriguez, Gabriel, Aragón, Rodrigo, Arranz, Miguel A., Rebollar, Esther, Castillejo, Marta, Colino, Jose M.
• Format: Article
• Language: English
• Subjects: Anisotropy; Demagnetization; Ferrous alloys; Film thickness; Foils; Laser induced periodic surface structures; Linear arrays; Magnetic alloys; Magnetic thin films; Magnetization; Magneto-optical effects; Modelling; Morphology; Periodic variations; Polyethylene terephthalate; Pulsed lasers; Ripples; Sputtering; Surface preparation; Thin films; Uniaxial magnetic anisotropy
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2020.167149

•New ripple nanostructure made by means of a scalable laser irradiation technique.•Shape induced uniaxial magnetic anisotropy solely driven by volume-like poles.•Anisotropic media made so that the role of surface contributions is ruled out. Advanced materials often involve multi-dependent approaches, merging electrical, optical and magnetic responses in nanostructured systems. To this purpose we have explored a semi-transparent, soft magnetic thin film (Permalloy) of nano-undulated morphology with which uniaxial anisotropy can be induced and tuned. This media is grown on the ripple surface of flexible, polymeric foil of polyethylene terephthalate (PET) that was previously patterned by a versatile pulsed-laser irradiation technique achieving a linear array with periodicity 220–250 nm and large amplitudes around 45 nm. Vectorial Kerr (reflection) as well as Voight (transmission) magneto-optical effects confirm a complete uniaxial anisotropy induced with easy axis along the ripple pattern for Py films of thickness ranging from 10 to 30 nm. Analysis of curved magnetic systems is a major challenge, so we need to combine measurements of surface magnetization with thorough micromagnetic modelling of a quasi-infinite ripple film (same dimensions as the media). Remarkably, our modelling indicates unique features confirmed by experiments; namely, two disparate demagnetizing fields in hard axis magnetization and a distinctive thickness evolution. These findings are characteristic of an undulated magnetic state with the uniaxial anisotropy driven by volume-like poles. The choice of large pattern dimensions has made possible to realize the undulated state where the anisotropy strength can simply be tuned with film thickness without any role of surface contributions. This approach to anisotropy engineering provides ground for applications design without the limitations of surface preparation.