Just 50°C decides whether an ultrathin magnetic film stays flat or falls apart
Magnetic storage technologies, which store information in the direction of magnetization, play an essential role in modern data storage. Hard disk drives (HDDs) are widely used for long-term storage, ...
Magnetic storage technologies, which store information in the direction of magnetization, play an essential role in modern data storage. Hard disk drives (HDDs) are widely used for long-term storage, while nonvolatile magnetic random-access memory (MRAM) is emerging as a promising alternative to flash memory.
These devices rely on epitaxial ultrathin magnetic alloy films in which two atomic species are arranged in alternating layers along a single crystallographic direction. This structure creates a large magnetocrystalline anisotropy energy (MAE), making the magnetic state more stable and preventing stored bits from accidentally flipping.
The more perfectly ordered the atomic arrangement—measured by the degree of L10 ordering—the greater the MAE and thermal stability of each magnetic bit.
However, producing films with both a high degree of L10 ordering and an atomically flat surface has remained a major challenge. High-temperature heating improves atomic ordering but also makes the film rougher as grains grow larger.
In a study made available online in the Journal of Alloys and Compounds, researchers from the University of Toyama in Japan investigated how ultrathin 5-nm-thick L10-FePd films evolve during a two-step heating process. The study was led by Professor Hiroshi Naganuma of the University of Toyama.
L10-FePd films are particularly promising for MRAM because their low magnetic damping allows their magnetization to be switched using very little energy.
Heating in two stages
Unlike conventional methods, the two-step heating process avoids exposing the film to high temperatures throughout its growth. Critically, the team also investigated the role of a nanoscale phenomenon known as solid-state dewetting (SSD), in which atoms diffuse across ultrathin films during heating, causing the continuous film to break into holes or isolated islands if its surface free energy is much higher than that of the underlying substrate.
"Although SSD is more pronounced in thin films, there have been no reports on the influence of SSD on the two-step heating process for L10-FePd alloy epitaxial films below a thickness of 5 nm," Naganuma says.
The researchers fabricated the films using radio-frequency magnetron sputtering. They first deposited Fe and Pd atoms onto a strontium titanate substrate at a relatively low temperature. Under these conditions, the atoms remained close to where they first landed, allowing the film to grow smoothly layer by layer.
After cooling the sample to room temperature, the researchers heated it to 600°C (1,112°F). This second heating step provided enough energy for the Fe and Pd atoms to rearrange into the highly ordered L10 crystal structure.
A 50-degree turning point
The researchers found that changing the first heating temperature by just 50°C strongly influenced how the film evolved during the second annealing step.
At 150°C (302°F), the film remained smooth and continuous, growing layer by layer in what is known as the Frank–van der Merwe growth mode. At 200°C (392°F), atomic diffusion became sufficient to initiate SSD, allowing the film to achieve nearly perfect L10 ordering while forming square holes that penetrated into the substrate. At 300°C (572°F), the film evolved into a rough, island-like morphology.
First-principles calculations revealed that SSD is driven by the surface free-energy difference between the film and substrate but begins only when defects formed during the first heating step trigger the process.
Different paths for storage devices
The findings show that controlling the first heating temperature provides a simple way to tune the structure and magnetic properties of ultrathin FePd films. For instance, the researchers state that films grown at 150°C (302°F) are best suited for MRAM because of their flat surface and strong perpendicular magnetic anisotropy. In contrast, the controlled SSD observed at 200°C (392°F) could enable self-organized magnetic structures for next-generation high-density storage devices.
This strategy could help develop ultra-low-power magnetic recording materials for future HDDs and MRAM, increasing storage density while reducing energy consumption.
"These findings offer a strategic blueprint for leveraging nanoscale thermodynamic instabilities based on the two-step heating process to offer new routes to engineer magnetic anisotropy and nanostructures in spintronic devices," Naganuma says.
More information
Samuel Vergara et al, Harnessing two-step heating and solid-state dewetting for highly ordered L10-FePd alloy epitaxial films, Journal of Alloys and Compounds (2026). DOI: 10.1016/j.jallcom.2026.189751
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Citation: Just 50°C decides whether an ultrathin magnetic film stays flat or falls apart (2026, August 7) retrieved 7 August 2026 from https://phys.org/news/2026-08-50c-ultrathin-magnetic-stays-flat.html
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