Ferromagnetic resonance of exchange-coupled perpendicularly magnetized bilayers

Abstract

Strong ferromagnetic interlayer exchange couplings $J$ in perpendicularly magnetized systems are becoming increasingly desirable for applications. We study whether ferromagnetic interlayer exchange couplings can be measured by a combination of broadband ferromagnetic resonance methods and magnetometry hysteresis loops. For this we model the switching and the eigenexcitations in bilayer systems comprising a soft layer coupled to a thicker harder layer that possesses higher perpendicular magnetic anisotropy. For large $J>0$ the switching fields are essentially independent of $J$ but the frequency of the optical eigenmode of the bilayer and the linewidth of the acoustical and optical eigenmode are directly sensitive to the coupling. We derive a corpus of compact analytical expressions to analyze these frequencies, their linewidth and discuss the meaning thereof. We illustrate this corpus on a system mimicking the fixed layers of a magnetic tunnel junction meant for spin torque applications.

References in corpus (2)

• Time-resolved spin-torque switching in MgO-based perpendicularly magnetized tunnel junctions
• Magnetization damping in noncollinear spin valves with antiferromagnetic interlayer couplings

Cited by in corpus (5)

• Back-hopping in Spin-Transfer-Torque switching of perpendicularly magnetized tunnel junctions
• Offset fields in perpendicularly magnetized tunnel junctions
• Ferromagnetic resonance study of composite Co/Ni - FeCoB free layers with perpendicular anisotropy
• Using rf voltage induced ferromagnetic resonance to study the spin-wave density of states and the Gilbert damping in perpendicularly magnetized disks
• Spin-torque nano-oscillator based on two in-plane magnetized synthetic ferrimagnets