Ultrafast optical study of spin wave resonance and relaxation in a CoFe/PtMn/CoFe trilayer film

Abstract

We report on our recent study of confined spin wave excitations in a 200 Å CoFe/PtMn/CoFe trilayer film by ultrafast Kerr-rotation experiments. Coherent magnetization precessions were generated and detected by subpicosecond laser pulses. Three precession modes are observed when a magnetic field is oriented in the film plane. The frequencies of two modes increase with the field, while one mode shows no field dependence. The modes are assigned to the exchange-dominated spin wave excitations and the nonhomogeneous dipole mode. We used a comprehensive model of the magnetic eigenmodes and their coupling to light to gain values of the exchange, bulk, and surface anisotropy constants. Further, we investigated spin wave relaxation as a function of the applied field. We calculated an effective damping constant for the uniform precession to be α∼0.012.

Prediction of Deterministic All-Optical Switching of Ferromagnetic Thin Film by Ultrafast Optothermal and Optomagnetic Couplings

“…In particular, ultrafast optical manipulation of magnetization has emerged as an exciting direction in modern magnetism, since the discovery of ultrafast demagnetization of a nickel film by a 60-femtosecond laser pulse 12 . Subsequent work not only confirmed the effect 16 – 19 , but also demonstrated the possibility to optically generate coherent magnetic precession 20 , 21 and optically induce spin reorientation 22 . One of the widely-discussed topics in ultrafast magnetization manipulation is that circularly polarized laser pulses can directly and deterministically switch magnetic domains without applying external magnetic field 23 – 25 .…”