Oscillatory dynamics of the magnetic moment of a Pt/Co/Ir/Co/Pt synthetic antiferromagnet

In this paper, we present a detailed study of the oscillating magnetic relaxation in the synthetic antiferromagnet (SAF) with two ferromagnetic Co layers of different thicknesses separated by an Ir spacer. The four stable magnetic states of the SAF are determined by the mutual alignment of magnetic moments in the layers and are controlled by both the magnetic interlayer exchange interaction and the Zeeman energy. The specific variations in the thicknesses of the layers and/or temperature allow the existence of a "triple point," which corresponds to a coincidence of the critical switching fields for two or three interstate transitions. In this case, two or even three different types of magnetization reversals occur simultaneously and competitively. A nonmonotonic dependence of the domain-wall speed vDW on magnetic field H and an oscillating time dependence of magnetic moment M in a constant magnetic field were observed in a Pt/Co/Ir/Co/Pt synthetic antiferromagnet with perpendicular anisotropy due to interplay between the magnetic nuclei produced by Dzyaloshinskii-Moriya interaction. The proximity of two or three (triple-point) critical fields of SAF switching is the necessary condition for both a nonmonotonic magnetic relaxation and the oscillating time variations of the magnetic moment. The dynamical model describing the interaction and subsequent evolution of the magnetic nuclei demonstrates that this nontrivial magnetic relaxation obeys a simple Schrödinger equation. © 2019 American Physical Society.1

Ferromagnetic resonance of CoFeB/Ta/CoFeB spin valves versus CoFeB film

International audienceIn MgO/CoFeB/MgO/Ta (single layer) and MgO/CoFeB/Ta/CoFeB/MgO/Ta spin valve (bilayer), the orientation dependences of ferromagnetic resonance (FMR) have been analyzed. Magnetic anisotropy constants as well as damping constants have been extracted. The differences between the anisotropy constants in single-layer film and spin valve MgO/CoFeB/Ta/CoFeB/MgO/Ta are explained by dipole magnetic interaction between ferromagnetic layers. The main part of the linewidth corresponds to inhomogeneous widening, while smaller part is provided by interface exchange fluctuations. The FMR lineshape can be explained by standard FMR Lorenz line and nonresonant absorption provided by inverse spin Hall effect

Effect of Co layer thickness on magnetic relaxation in Pt/Co/Ir/Co/Pt/GaAs spin valve

International audienceLong magnetic relaxation (up to few hours) between stable magnetic states was analyzed in Pt/Co/Ir/Co/ Pt/GaAs heterostructures of different Co layers thickness. The experimental data were compared to a large variety of theoretical models amongst which the Fatuzzo-Labrune one seems to be the more relevant. The contributions from domain nucleation and domain wall motion to magnetic relaxation of the spin valves were separated and evaluated. The increase of Co layer thickness suppresses the domain nucleation and enhances the domain wall propagation. The obtained data provide an understanding of the limitations of switching time in the spin valves of large area necessary for GMR biosensors