Spin-waves in magnetic nanostructures: Epitaxial Fe monolayer, double layer and nanoislands on W(110)

Quasiparticles play a fundamental role in nature. In magnetism, elemental magnetic collective excitations (magnons) are essential for explaining magnetic ordering and electron-/spin-dynamics. The magnons in low dimensions are of great importance also for modern nano-devices, where spin-transfer-torque processes are used to write the magnetic information. Of particular interest are high wave vector excitations that are determined by exchange interaction, and occur on the scales of femtoseconds and nanometers. We report the observation of magnon excitations in epitaxially grown Fe nanostructures on W(110) for the first time. We directly show that the magnons in the Fe monolayer (ML) are softer than the surface Fe(110) mode. Our observations are in sharp contrast to theoretical calculations, which predict much higher magnon energies. Pronounced features of magnon peaks are observed in the spectra of double layer (DL). We found that the magnon energies in DL are also strongly reduced compared to the ones in bulk Fe and to theoretical predictions. This reduction is caused by the reduction of exchange interaction within DL as compared to the bulk Fe. In the case of nanoisland, formed in the thickness range between 1.2 and 1.8 ML, it is found that the magnon intensity is proportional to the area of the DL regions, which indicates that the observed magnon signal is probed in these regions. Our results, which reveal the dispersion of the magnons over the entire Brillouin zone, are of general importance for the understanding of spin-wave dynamics in magnetic nanostructures.

Keywords:

Spin-waves , Magnons , Magnetic nanostructures