Finite size effects on spin-torque driven ferromagnetic resonance in spin-valves with a Co/Ni synthetic free layer

TL;DR

This study investigates how finite size effects influence spin-torque driven ferromagnetic resonance in Co/Ni synthetic layers within nanojunctions, revealing lower resonance fields compared to extended films and discussing dipolar and size effects.

Contribution

It provides new insights into the finite size effects on ST-FMR in nano-confined Co/Ni layers, comparing them with extended film behavior.

Findings

Lower resonance fields in confined structures compared to extended films

Finite size effects alter the spin wave spectrum

Dipolar fields influence magnetic resonance in nanojunctions

Abstract

Spin-torque driven ferromagnetic resonance (ST-FMR) is used to study magnetic excitations in Co/Ni synthetic layers confined in nanojunctions. Field swept ST-FMR measurements were conducted with a magnetic field applied perpendicular to the layer surface. The resonance lines were measured under low amplitude excitation in a linear response regime. The resulting resonance fields were compared with those obtained using conventional rf field driven FMR on extended films with the same Co/Ni layer structure. A lower resonance field is found in confined structures. The effect of both dipolar fields acting on the Co/Ni layer emanating from other magnetic layers in the device and finite size effects on the spin wave spectrum are discussed.