Rotatable anisotropy of FePt thin films grown on PMN-PT

ANA SARMIENTO; JAVIER E. GÓMEZ; DAFNE GOIJMAN; D. LACOUR; M. HEHN; A. BUTERA; J. MILANO

Bariloche

Workshop; International workshop on Spintronics 2022; 2022

Centro Atómico Bariloche

Thin films of FePt are currently the subject of a number of experimental investigations due to their peculiar magnetic properties, i.e., very large coercivities and high-magnetic anisotropy. Among the features of these ferromagnetic films, above a critical thickness the magnetic domain structure changes from a planar structure to a periodic bands array, called weak stripes. This stripe pattern consists of an alternating up and down magnetization components and closure domains between adjacent perpendicular domains.One of the interesting properties of this kind of pattern is the fact that the stripe direction on the sample is along the direction where the last saturating field was applied. This phenomenon is called “rotatable anisotropy”, and it was first observed in vapor-deposited thin permalloy films [1].One of the options to study the rotatable anisotropy is by growing the FM film on a piezoelectric substrate. This type of substrate deforms anisotropically with a nonzero remanent strain upon the application of an electric field. Due to the magnetoelastic coupling, the deformation in the piezoelectric causes a change in the magnetic anisotropy of the film. Our research group reported [2] that for a chemically disordered FePt ferromagnetic films that have been sputter-deposited on a piezoelectric substrate it is possible to switch the magnetization easy axis by 90◦ if an electric field is applied in a direction perpendicular to the film plane. Although this FePt system on PMN-PT has already been grown, until now it hasn’t been explored how the stripes rotate, not by changing the direction of the magnetic field, but rather by applying a stress to the substrate.For this study, thin FePt films have been grown with a range of thicknesses (25-60 nm) that go from samples without stripes to samples with stripes. These samples have been characterized by various techniques such as Ferromagnetic Resonance (FMR), Vibrating Sample Magnetometer (VSM), Magneto Optical Kerr Effect (MOKE) and Magnetic Force Microscope (MFM). To observe how generating piezoelectric stress affects rotational anisotropy, all measurements were made without and with applying stress, emphasizing samples with thicknesses close to the critical thickness.References[1] R. J. Prosen, J. O. Holmen, and B. E. Gran , "Rotatable Anisotropy in Thin Permalloy Films", Journal of Applied Physics 32, S91-S92 (1961) https://doi.org/10.1063/1.2000512.[2] L. Leiva, J.L. Ampuero Torres, J.E. Gómez, D. Velázquez Rodriguez, J. Milano, A. Butera, Electric field control of magnetism in FePt/PMN-PT heterostructures, Journal of Magnetism and Magnetic Materials, Volume 544, 2022, 168619, ISSN 0304-8853, https://doi.org/10.1016/j.jmmm.2021.168619.