Research results, Scientific Publications

A new study reveals that insulating buffer layers are no longer needed for ultrathin magnetic racetrack devices, unlocking new paths for seamless integration with functional substrates.

To the point:

_Eliminating the insulating MgO buffer layer, ultrathin Platinum-Cobalt-Nickel membranes directly interface with pre-patterned substrates while retaining their magnetic properties.
_New approach towards integration with functional and flexible substrates for memory devices
_These breakthrough results from researchers of the NISE Department, led by Prof. Stuart Parkin, were recently published in Advanced Materials

Modern computing devices rely on memory technologies that are not only energy-hungry but physically separated from the processing units - leading to inefficiencies in speed and power. A promising alternative lies in spintronics, particularly racetrack memory (RTM), where data is stored in the form of movable magnetic domain walls (DWs) along nanowire-like “tracks.” These devices are non-volatile, energy-efficient, and can potentially unify memory and logic on a single chip.

To expand the design flexibility and integration potential of such devices, researchers have explored using freestanding membranes - thin films that are lifted off from their original substrates and transferred onto receiving surfaces, including patterned bases with 3D structures [1]. However, this process usually requires a buffer layer, such as magnesium oxide (MgO), to support high-quality magnetic layer growth. The buffer, while useful during fabrication, acts as an insulating barrier in the final device, preventing electrical or magnetic interaction with the underlying transfer bases.

In a recently published paper in Adv. Mater. [2], scientists from the Max Planck Institute of Microstructure Physics have shown that this buffer layer is no longer necessary. In their new study, they demonstrate that a sacrificial oxide layer - Sr₃Al₂O₆ (SAO) - can directly support the growth of high-performance magnetic multilayers (Pt/Co/Ni/Co), enabling the fabrication of freestanding racetrack memory devices without any buffer layer. Remarkably, these buffer-free membranes exhibit better DW mobility than their buffered counterparts - despite being less than 4 nm thick.

A step further: the team transferred these membranes onto pre-patterned Pt underlayers, showing that the DW dynamics could be locally engineered - a key capability for future racetrack-based logic and memory architectures.

The study also confirms the remarkable robustness of these ultrathin racetracks. Devices maintain their performance after repeated mechanical bending, long-term ambient air exposure, thermal annealing, and electrical stress. The research not only deepens the understanding of interface engineering in freestanding magnetic films, but also opens a pathway to vertical or lateral coupling with functional substrates. This advances the vision of highly integrated, high-density spintronic devices.

[1] https://www.nature.com/articles/s41565-022-01213-1

[2] https://advanced.onlinelibrary.wiley.com/doi/full/10.1002/adma.202505707

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Wissenschaftlicher Ansprechpartner:
ke.gu@mpi-halle.mpg.de

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Originalpublikation:
https://advanced.onlinelibrary.wiley.com/doi/10.1002/adma.202505707

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Weitere Informationen:
https://www.mpi-halle.mpg.de/841048/2025-08-05-research-news-ke-gu?c=160677