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Abstract Spin-orbit torques (SOTs) have been widely understood as an interfacial transfer of spin that is independent of the bulk properties of the magnetic layer. Here, we report that SOTs acting on ferrimagnetic Fe x Tb 1- x layers decrease and vanish upon approaching the magnetic compensation point because the rate of spin transfer to the magnetization becomes much slower than the rate of spin relaxation into the crystal lattice due to spin-orbit scattering. These results indicate that the relative rates of competing spin relaxation processes within magnetic layers play a critical role in determining the strength of SOTs, which provides a unified understanding for the diverse and even seemingly puzzling SOT phenomena in ferromagnetic and compensated systems. Our work indicates that spin-orbit scattering within the magnet should be minimized for efficient SOT devices. We also find that the interfacial spin-mixing conductance of interfaces of ferrimagnetic alloys (such as Fe x Tb 1- x ) is as large as that of 3 d ferromagnets and insensitive to the degree of magnetic compensation.
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Atomistic modeling of temperature dependent coercivity and switching behavior in compositionally modulated CoGd alloys
Vertically inhomogeneous single layer ferrimagnetic films have emerged as exciting building blocks of potential next generation spintronic devices, owing to the observations of single layer switching driven by bulk spin–orbit torques resulting from broken inversion symmetry. However, little work has been performed to understand the role composition gradients play in determining the bulk and local magnetic properties of these films, as well as how changes introduced through composition gradients influence the switching behavior. We utilize atomistic spin simulations to explore how the local magnetization varies in CoGd alloys, both due to the decreased coordination number at surfaces and due to vertical inhomogeneities, and how this influences the switching fields in these films. While compositional modulation varies the local compensation point through the film thickness, it has no significant effect on the net compensation temperature of the alloy if the average composition stays the same, even with large variations. However, even minor variations in composition can drastically reduce the out-of-plane coercivity or even preclude perpendicular anisotropy entirely. Furthermore, the direction of the gradient determines the surface on which field driven magnetization reversal initiates, which can have design implications for future devices. This provides new insights into the role that composition gradients in ferrimagnetics play in magnetization reversal.
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- Award ID(s):
- 2138271
- PAR ID:
- 10598584
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- AIP Advances
- Volume:
- 15
- Issue:
- 6
- ISSN:
- 2158-3226
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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