Anisotropy engineering of soft thin films in the undulated magnetic state

8 pags., 6 figs.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.The authors gratefully acknowledgefinancial support from the Spanish Ministry of Economy and Competitiveness, MINECO, (grantsnumber: MAT2015-65295-R and CTQ2016-75880-P). E.R. also thanksMINECO for a Ramón y Cajal contract (RYC-2011-08069