Reduction of Magnetoelastic Constant B2 in Fe Thin Films by Nitrogen-Implantation, as determined by surface acoustic waves

This article presents an original approach to both modify and measure the magnetoelastic coupling constant B2 in epitaxial nitrogen-implanted Fe thin films presenting the α′-Fe8N1-x phase. Once the magnetocrystalline anisotropy has been determined by standard techniques, we measure the field-dependence of Rayleigh surface acoustic wave (SAW) velocity variations. The magnetoelastic coupling constant is extracted by fitting the field-angle dependence of these variations. Using the magnetic and magneto-elastic parameters thus determined, the variations in SAWvelocity as a function of the external field seen in surface acoustic wave induced ferromagnetic resonance (SAW-FMR) experiments can be accurately reproduced, both in pristine and nitrogen-implanted Fe thin films. This ensemble of results confirms a reduction by almost half of the magnetoelastic coupling under doping level 2×1016 N2/cm2.