Surface anisotropy and spin wave resonance in submicron amorphous wires

• Published in: Journal of magnetism and magnetic materials Vol. 473; pp. 284 - 290
• Main Authors: Kraus, Luděk, Kopeček, Jaromír
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.03.2019; Elsevier BV
• Subjects: Anisotropy; Circular cylinders; Cylindrical coordinates; Dependence; Ferromagnetic resonance; Ferromagnetism; Glass; Magnetic anisotropy; Magnetism; Magnons; Microwave frequencies; Nanowires; Spin waves; Stiffness; Submicron amorphous wires; Surface anisotropy; Ferromagnetic resonance; Submicron amorphous wires; Spin waves; Surface anisotropy
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2018.10.045

•FMR spectra of submicron amorphous wires exhibit fine structure due to excitation of standing spin waves.•From the period of fine structure the exchange stiffness constant can be determined.•The perpendicular surface anisotropy leads to the appearance of surface spin wave mode on the high field side of the spectra.•Experimentally observed resonance curves satisfy well the theoretical calculations. The influence of surface magnetic anisotropy on ferromagnetic resonance (FMR) in submicron wires is investigated both theoretically and experimentally. An analytical formula for resonance fields of radial spin waves in a long axially magnetized circular cylinder is obtained. Three types of surface anisotropy with the easy direction along one of the cylindrical coordinates are considered. For sufficiently strong surface anisotropy with hard direction parallel to the cylinder axis the surface spin wave mode is observed. The theoretical results are verified by FMR measurements at six microwave frequencies from 9 to 69 GHz on glass-covered amorphous FeCrSiB wires with diameters from 541 to 1032 nm. From the bulk spin wave resonances the exchange stiffness constant about 6.5 10−7 erg/cm is obtained. The frequency dependence of the surface mode resonance field indicates that a perpendicular surface anisotropy with anisotropy constant Ks = 6.2 erg/cm2 is present at the metal/glass interface.