Thermally excited spin wave modes in synthetic antiferromagnetic stripes

Brillouin light scattering (BLS) microscopy studies were performed on patterned synthetic antiferromagnetic (SAF) films. SAF films with the stacking structure of SiO₂/Ta(5 nm)/FeNi(6.8 nm)/Ru(0.4 nm)/FeNi(3.6 nm)/Ru(3 nm) were prepared using magnetron sputtering and were patterned into a stripe shape with a width of 2 μm. We measured the micro-BLS spectra at the center and the edge positions of the SAF stripe in a static magnetic field of 950 Oe applied perpendicular to the long axis. The spin wave frequencies of the SAF stripe decrease in comparison with those of the single FeNi film stripe. The difference between the spin wave frequencies at the center and at the edge is relatively small in the SAF samples, which is indicative for SAF films with small stray fields. Micromagnetic simulations provide a good account for the experimental observations.