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Thin films composed of sputtered transition metal/rare earth (TM/RE) ferrimagnets have emerged as promising building blocks for future spintronic devices, offering tunable magnetic properties critical for data storage, memory, and logic applications. However, understanding how the combination of TM and RE elements influences effective magnetic properties, such as exchange stiffness (Aex), remains challenging. Magnetic vortices provide a versatile tool for probing these properties in thin film systems. By combining magnetic imaging via soft x-ray microscopy and micromagnetic modeling, we quantify the effective exchange stiffness in PyGd ferrimagnetic disks with varying Gd concentrations. Our results indicate a reduction in Aex to below 3 pJ/m for a 20% Gd concentration when compared to reference Py, and values below 2 pJ/m for 30% Gd, reflecting weak Ni–Gd exchange coupling. These findings highlight the critical role of rare earth content in tuning the exchange stiffness. The reduced exchange stiffness facilitates a linear field response of the magnetization up to the edge of the disk, as well as significant deformations in the vortex core itself when compared to films with larger Aex. Our results are in line with, albeit lower than, recent measurements of the exchange stiffness in intermixed PyGd. This reduced exchange stiffness has implications for the development of spintronic devices based on ferrimagnetic skyrmions. 

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.