Relaxation and aging of a superferromagnetic domain state

Abstract

In agreement with recent model calculations on interacting magnetic nanoparticles the magnetic relaxation of a field-cooled superferromagnetic (SFM) granular multilayer $[{\mathrm{Co}}_{80}{\mathrm{Fe}}_{20}(1.4\mathrm{nm})/{\mathrm{Al}}_{2}{\mathrm{O}}_{3}(3\mathrm{nm}){]}_{10}$ follows a power-law decay retaining a finite asymptotic remanence. Unexpectedly, a second isothermal upward relaxation is observed after field quenching the sample. It is attributed to slow equilibration of the thermoremanent magnetization inside the SFM domains. Magnetization hole burning via aging reveals the chaotic nature of the domain state.