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 magnetoelastic parameters thus determined, the variations in SAW velocity as a function of the external field seen in surface acoustic wave induced ferromagnetic resonance 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.