Compositional Analysis of Pt1-XCox Thin Film with Single Deposition, Combinatorial Co-Sputter Technique
Authors: Martinez William M. , Larson Steven R , Kellogg Rick A. , Huber Dale L. , Kodigala Ashok 
Published: August 2024

Applications of thin-film magnetic materials often have narrow windows that the magnetic characteristics (i.e., remnant magnetization and coercive field) must meet – for instance magneto-optical devices [1] with latching operations [2] or amplitude- [3] or phase-control [4] of superconducting-ferromagnetic hybrid systems for next-generation computing memory. As systems become more complex, manipulating magnetic layers without affecting the rest of the device becomes increasingly challenging. Alloys of magnetic materials can alleviate this but determining viability – whether an alloy has any composition that can meet design needs – requires fabricating and analyzing samples that span the compositional space.

Despite the community utilizing high-throughput methods for decades, including for thin-film materials [5], most exploratory research is still conducted by creating one composition per run, varying relative power or time during a deposition, for example. Obtaining a library of samples that vary in subtle but non-trivial ways becomes time-intensive, often prohibitive, and the resulting data set is prone to systematic errors that result from run-to-run variations. High-throughput methods, especially those that can produce a breadth of variation in a single fabrication or synthesis run, can expedite the discovery phase and reduce errors that complicate comparative analysis.

One method that can provide, in a single run, a broad range of compositions for a material system is combinatorial fabrication using oblique angle co-deposition [6]. Using this method, we co-sputtered samples using targets of elemental Pt and Co to obtain PtCo thin film (Figure 1a). During deposition, the wafer is not rotated, relying instead on the target and sample geometry in the chamber to provide compositional variation across the wafer. After unloading and dicing our test wafer into 4mm-by-4mm samples, we ran XRD of multiple samples to determine thickness and composition of the thin film alloys as a function of position (Figure 1b).

Across an 8” wafer, this technique yielded Pt1-xCox thin film between 5% and 83% atomic composition Co. A subset of samples (68 nm < t < 117 nm, where t is the PtCo thickness) were measured with VSM up to 1 T applied field to obtain B-H curves (Figure 1c), from which the remnant magnetization and coercive field characteristics relative to composition were extracted (Figure 1d). We find that remnant magnetization varies from 0 T to about 0.6 T, mostly increasing as %Co increases. Coercivities vary between 0 Oe and 1800 Oe, maximized at about 50% Co. Because the samples were fabricated in the same run, all samples are free from run-to-run variations and differences in processing, and thus they can be compared directly. Utilizing this technique, we were able to determine the viability window of Pt1-xCox films for nearly all compositions (5%-83% Co) in a single run.

Figure 1 a) Sputtering system running combinatorial Co-Pt growth. b) Thickness and atomic%-composition of Co relative to sample location. c) J-H curve for 66at% Co. d) Remnant magnetization (JR) and coercive field (H0) for Pt1-xCox , 0.05 < x < 0.83.

Acknowledgement: This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. This work is supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This written work is authored by an employee of NTESS. The employee, not NTESS, owns the right, title and interest in and to the written work and is responsible for its contents. Any subjective views or opinions that might be expressed in the written work do not necessarily represent the views of the U.S. Government. The publisher acknowledges that the U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this written work or allow others to do so, for U.S. Government purposes. The DOE will provide public access to results of federally sponsored research in accordance with the DOE Public Access Plan.

Figure 1