“Acoustical” and “optical” spin modes of multilayers with antiferromagnetic coupling and evidence for Goldstone excitations -- Presentazione poster by R. Zivieri - Conferenza nazionale

A study of the in-phase (“acoustical”) and of the out-of phase (“optical”) spin modes in layered ferromagnetic structures with both ferromagnetic and antiferromagnetic coupling is presented, in particular for the system Fe(20 Å)/Cr(20 Å)/Fe(20 Å)/Cr (9 Å)/Fe(100 Å). A calculation of the dynamic magnetization assumed constant in each film gives an explanation of the behavior of the two kind of modes at different magnetic fields applied along the easy axis. The “acoustical” mode is present at low fields, but frequency exchanges with the “optical” modes occur at higher fields. It is found that the competition between the Zeeman and the biquadratic exchange terms is responsible for the appearance of a Goldstone mode at a critical field marking a second-order phase transition. -- Presentazione poster by R. Zivieri - Conferenza nazionale