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.