4.7 Article

Vanadium trapped by oblique nano-sheets to preserve the anisotropy in Co-V thin films at high temperature

Journal

JOURNAL OF ALLOYS AND COMPOUNDS
Volume 911, Issue -, Pages -

Publisher

ELSEVIER SCIENCE SA
DOI: 10.1016/j.jallcom.2022.164950

Keywords

Thin films; Nano-fabrications; Anisotropy; Electrical transport; Scanning tunnelling microscopy; STM; Transmission electron microscopy; TEM; Electron energy loss spectroscopy; EELS

Funding

  1. Public University of Navarre
  2. Spanish Ministerio de Economia y Competitividad [MAT2017-82970-C1, C2-R]
  3. Aragon Regional project [E26]
  4. Universidad Publica de Navarra

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In this study, the effects of oriented nano-sheets generated during the growth of cobalt-rich Co-V and Co-Zn thin films on magnetic and transport properties were investigated. It was found that the anisotropy of the nano-sheet morphology resulted in noticeable shape anisotropy in the films. Thermal treatments caused changes in the nano-morphology and the associated anisotropic properties.
In this study, oriented nano-sheets generated during the growth of cobalt-rich Co-V and Co-Zn thin films induced a large anisotropy in the magnetic and transport properties. The regular nano-sheets were tilted 52-54 deg. with respect to the substrate plane, approximate to 3.0-4.0 nm thick, approximate to 30-100 nm wide, and approximate to 200-300 nm long, with an inter-sheet distance of P, 0.9-1.2 nm. In spite of the different microstructures of the two kinds of samples where the Co-V films were amorphous, whereas the Co-Zn films showed a growth of Zn nanocrystals, the oblique nano-sheet morphology conferred noticeable shape anisotropy to both specimens. This anisotropy resulted in an in-plane uniaxial magnetic anisotropy. The changes in the nano-morphology caused by thermal treatments, and hence in their anisotropic properties, were studied. While the Co-V samples retained or increased their magnetic and transport anisotropies, this anisotropic behavior vanished for the annealed Co-Zn films. High resolution transmission electron microscopy, HRTEM, including chemical analysis at the nano-scale, and the dependence of the anisotropic resistance on temperature allowed to establish the nature and the activation energy spectra of the atomic relaxation processes during heating. These processes displayed a single peak at 1.63 eV for the Co-V and two peaks at 1.67 and 2.0 eV for the Co-Zn. These spectra and their singularities were associated to the changes induced in the nano-morphology of the films by thermal treatments. The Co-V films retained their nano-sheet morphology almost up to 500 (?)degrees C; the Co-Zn films lost their nano-sheets at 290 degrees C. The thermal stability exhibited by the Co-V films makes them useful for applications in ultra high frequency, optical, magnetostrictive and magneto electric devices. (c) 2022 The Author(s). Published by Elsevier B.V.

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