Scientists Develop an “Extended Landau Free Energy Model” for Advanced Materials Design

Explainable AI-Based Physical Theory for Advanced Materials Design

Scientists develop an “extended Landau free energy model” for causal analysis and visualization in nano-magnetic devices with AI and topology.

Microscopic materials analysis is essential to achieve desirable performance in next-generation nanoelectronic devices, such as low power consumption and high speeds. However, the magnetic materials involved in such devices often exhibit incredibly complex interactions between nanostructures and magnetic domains. This, in turn, makes functional design challenging.

Traditionally, researchers have performed a visual analysis of the microscopic image data. However, this often makes the interpretation of such data qualitative and highly subjective. What is lacking is a causal analysis of the mechanisms underlying the complex interactions in nanoscale magnetic materials.

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An image depicting the extended Landau free energy model developed by a research team from Tokyo University of Science, which enables a causal analysis of the magnetization reversal in nanomagnets. Through this model, the team could visualize magnetic domain images effectively and were successful in the inverse designing of nanostructures with low energy requirements. Credit: Kotsugi Laboratory from Tokyo University of Science, Japan

In a recent breakthrough, a research team succeeded in automating the interpretation of the microscopic image data. This was achieved using an “extended Landau free energy model” that the team developed using a combination of topology, data science, and free energy. The model could illustrate the physical mechanism as well as the critical location of the magnetic effect, and proposed an optimal structure for a nano device. The model used physics-based features to draw energy landscapes in the information space, which could be applied to understand the complex interactions at the nanoscales in a wide variety of materials. Details of the study will be published today (November 29) in the journal Scientific Reports. The research was led by Prof. Masato Kotsugi from the Tokyo University of Science in Japan.

“Conventional analysis are based on a visual inspection of microscope images, and the relationships with the material function are expressed only qualitatively, which is a major bottleneck for material design. Our extended Landau free energy model enables us to identify the physical origin and location of the complex phenomena within these materials. This approach overcomes the explainability problem faced by deep learning, which, in a way, amounts to reinventing new physical laws,” Prof. Kotsugi explains. This work was supported by KAKENHI, JSPS, and the MEXT-Program for Creation of Innovative Core Technology for Power Electronics Grant.

Scatterplot of the dimensionality reduction results of principle component analysis. Color represents the total energy. The relationship between magnetic domain and total energy is connected in the explainable feature space. Credit: Masato Kotsugi from Tokyo University of Science, Japan

When designing the model, the team made use of the state-of-art technique in the fields of topology and data science to extend the Landau free energy model. This led to a model that enabled a causal analysis of the magnetization reversal in nanomagnets. The team then carried out an automated identification of the physical origin and visualization of the original magnetic domain images.

Their results indicated that the demagnetization energy near a defect gives rise to a magnetic effect, which is responsible for the “pinning phenomenon.” Further, the team could visualize the spatial concentration of energy barriers, a feat that had not been achieved until now. Finally, the team proposed a topologically inverse design of recording devices and nanostructures with low power consumption.

The model proposed in this study is expected to contribute to a wide range of applications in the development of spintronic devices, quantum information technology, and Web 3.

Scatterplot of the dimensionality reduction results of principle component analysis. Color represents the total energy. The relationship between magnetic domain and total energy is connected in the explainable feature space. Credit: Masato Kotsugi from Tokyo University of Science, Japan

“Our proposed model opens up new possibilities for optimization of magnetic properties for material engineering. The extended method will finally allow us to clarify ‘why’ and ‘where’ the function of a material is expressed. The analysis of material functions, which used to rely on visual inspection, can now be quantified to make precise functional design possible,” concludes an optimistic Prof. Kotsugi.

Reference: “Causal Analysis and Visualization of Magnetization Reversal using Feature Extended Landau Free Energy” 29 November 2022, Scientific Reports.
DOI: 10.1038/s41598-022-21971-1

This study was supported by KAKENHI, JSPS [21H04656]. Part of this study was supported by MEXT-Program for Creation of Innovative Core Technology for Power Electronics Grant Number JPJ009777, and KAKENHI, JSPS [19K22117, 22K14590].