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Interlayer Exchange Coupling in Magnetic Hard-Soft Bilayered Structures

Daniel Richardson¹, Kumar Srinivasan², Alan Kalitsov², Antony Ajan², Shikha Jain², Sidney Katz¹, and Mingzhong Wu^1,*

¹Department of Physics, Colorado State University, Fort Collins, Colorado 80523, USA
²Western Digital, San Jose, California 95131, USA

^*mwu@colostate.edu

Phys. Rev. Applied 11, 044016 – Published 5 April, 2019

DOI: https://doi.org/10.1103/PhysRevApplied.11.044016

Abstract

Broadband ferromagnetic resonance (FMR) and high-temperature (T) FMR measurements are carried out to study interlayer exchange coupling (IEC) in a magnetic hard-soft bilayered system where the hard layer is a $Fe Pt$ thin film with strong perpendicular anisotropy and the soft layer is a thin film made of $Fe$ , $Co$ , or their alloys. The data indicate that the effective exchange field ( $H_{ex}$ ) produced by the IEC on the soft layer increases with a decrease in the thickness or saturation induction (4π $M_{s}$ ) of the soft layer. With an increase in T, $H_{ex}$ drops by an amount larger than 4π $M_{s}$ . The effective damping constant of the soft layer increases with $H_{ex}$ and can vary by two orders of magnitude. In samples with $H_{ex}$ > 4π $M_{s}$ , the damping constant is insensitive to the choice of material of the soft layer. In samples with $H_{ex}$ < 4π $M_{s}$ , the damping constant strongly depends on the choice of material. When T is increased from room temperature to the Curie temperature of the hard layer, the FMR linewidth drops significantly in samples where $H_{ex}$ is relatively large, but remains constant or even increases slightly at high T in samples where $H_{ex}$ is very small. The effects of $H_{ex}$ on the damping and linewidth can be understood by considering two distinct components in the overall damping, an intrinsic component mainly due to spin-flip magnon-electron scattering and an extrinsic component due to IEC-associated spin pumping at the interface.

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Interlayer Exchange Coupling in Magnetic Hard-Soft Bilayered Structures

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