This dataset contains the information on our recent body of work on the study of magneto-ionic engineering of antiferromagnetically RKKY-coupled multilayers and all the relevant data files. Magneto-ionics, an emerging approach to manipulate magnetism that relies on voltage-driven ion motion, holds the promise to boost energy efficiency in information technologies such as spintronic devices or future non-von Neumann computing architectures. Despite the technological potential of synthetic antiferromagnets (SAFs), magneto-ionic control of antiferromagnetic coupling in multilayers (MLs) has only recently been explored and remains poorly understood, particularly in systems free of platinum-group metals. In this work, we achieve room-temperature voltage control of Ruderman–Kittel–Kasuya–Yosida (RKKY) interactions in Co/Ni-based SAFs. We observe transitions between ferrimagnetic (uncompensated) and antiferromagnetic (fully compensated) states, as well as significant modulation of the RKKY bias field offset, emergence of additional switching events, and formation of skyrmion-like or pinned domain bubbles under relatively low gating voltages. These phenomena are attributed to voltage-driven oxygen migration in the MLs, as confirmed through microscopic and spectroscopic analyses. This study underscores the potential of voltage-triggered ion migration as a versatile tool for post-synthesis tuning of magnetic multilayers, with potential applications in magnetic-field sensing, energy-efficient memory devices, and spintronics.

1. Description of methods used for collection-generation of data: Various experimental tools were employed in this line of work, such as magnetron sputter for the materials growth, magnetometry for magneto-electric study, transmission electron microscopy for structural study, and positron annihilation spectroscopy for defect inspections.

2. Methods for processing the data: The data files can be processed using Origin software, PowerPoint, and DigitalMicrograph.

3. Instrument- or software- specific information needed to interpret the data: For the magnetometry data, any antiferromagnetic signals were subtracted using the VSM software in our lab. The format of this dataset was converted into an open format that can be processed using Origin software.

4. Instruments, calibration and standards information: The VSM magnetometer was calibrated using a standard nickel pallet provided by the company (Micro Sense, LOT, Quantum Design). Magnetization data is shown in the paper as magnetic moment divided by the effective volume of the films.

5. Environmental or experimental conditions: The measurements were conducted in ambient conditions.

6. Quality-assurance procedures performed on the data: The results were carefully analyzed and interpreted. Peer review process of the corresponding scientific article by experts in this field has been done, and its imminent publication in Advanced Materials is expected.