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Abstract The magnetic properties of permalloy-based trilayers of the form Py 0.8 Cu 0.2 /Py 0.4 Cu 0.6 /Py/IrMn were studied as the spacer layer undergoes a paramagnetic to ferromagnetic phase transition. We find the coupling between the free Py 0.8 Cu 0.2 layer and the exchange bias pinned Py to be strongly temperature-dependent: there is negligible coupling above the Curie temperature of the Py 0.4 Cu 0.6 spacer layer, strong ferromagnetic coupling below that temperature, and a tunable coupling between these extremes. Polarized neutron reflectometry was used to measure the depth profile of the magnetic order in the system, allowing us to correlate the order parameter with the coupling strength. The thickness dependence shows that these are interface effects with an inverse relationship to thickness, and that there is a magnetic proximity effect that enhances the Curie temperature of the spacer layer with characteristic length scale of about 7 nm. As a demonstration of potential functionality of such a system, the structure is shown to spontaneously flip from the antiparallel to parallel magnetic configuration once the spacer layer has developed long-range magnetic order.
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Investigating the dependence of the biquadratic exchange interaction on extrinsic factors in permalloy–ruthenium synthetic antiferromagnets
In this work, we extract the temperature-dependent bilinear J1 and biquadratic J2 exchange energy densities in permalloy–ruthenium-based synthetic antiferromagnet bilayers, trilayers, and tetralayers. In our samples, the ruthenium interlayer thickness is fixed to be 1 nm across all structures, but we consider permalloy layers that are 3 and 9 nm thick. To the best of our knowledge, this work represents the first time that the influence of both the ferromagnetic layer thickness as well as the total number of ferromagnetic layers on biquadratic exchange interactions has been examined together. Across all samples, we observe a significant increase in the strength of J2 relative to J1 as the temperature is lowered. We also observe trends indicating that J2 is sensitive to both the thickness and the total number of permalloy layers. Our analysis suggests that in structures with thicker and more numerous ferromagnetic layers, J2 originates from interfacial roughness effects between the magnetic layer and the spacer layer. In samples with thinner and less numerous permalloy layers, multiple mechanisms must contribute to J2. These findings provide new insights into the complexity of interlayer exchange interactions in synthetic antiferromagnets, which will aid in interpreting ongoing magnonic and spintronic experimental studies of synthetic antiferromagnets.
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- PAR ID:
- 10583363
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- Journal of Applied Physics
- Volume:
- 137
- Issue:
- 15
- ISSN:
- 0021-8979
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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