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日本語

Multiferroic materials combine electrical (ferroelectric) and magnetic (ferromagnetic) properties and have a strong correlation between these properties, i.e. they exhibit a magnetoelectric effect. Their development is expected to realize more versatile and higher performance next-generation electrical and magnetic devices. In recent years, several methods of production of multiferroic films exhibiting large magnetoelectric properties have been reported. However, these processes require large and extraordinarily expensive vacuum devices, making them impractical for fabricating materials with a large surface area in particular. As a result, multiferroic materials have only been used in a very limited range of applications.

The new material with advanced multiferroic properties developed by the research team, however, was created by combining several liquid-phase methods that are relatively inexpensive and simple.

The lead author, Associate Professor Go Kawamura of Toyohashi University of Technology explained, "In order to fabricate a material that exhibits advanced multiferroic properties, it is necessary to combine ferroelectric and ferromagnetic materials appropriately and periodically on the nanometer scale. In the past, nanopillar array structures were fabricated in a self-organized manner using gas-phase methods, and a large magnetoelectric effect was observed in such materials. However, the gas-phase methods required the use of large and expensive equipment, and it was practically impossible to increase the area of the sample. Therefore, we worked on the fabrication of nanopillar array-like composite films using only affordable and simple liquid-phase methods. We were able to demonstrate that the multiferroic composite film we created has a local epitaxial relationship at the interface between the ferroelectric and the ferromagnetic materials, thereby producing a large magnetoelectric effect. Compared to conventional gas-phase processes, multiferroic composite films can be produced at a much lower cost and can be used for larger areas."

This study required an interdisciplinary approach since it required expertise across a variety of specialties. Therefore, the research team collaborated with specialists in dielectric materials and magnetic materials, specialists in observation of nanostructures using electron microscopes, and specialists in liquid-phase synthesis, among others, from various institutions in Japan and overseas. The novel process was developed by combining these advanced specialties.

The research team believes that greater precision in the creation of controlled nanostructures can lead to a further improvement of the magnetoelectric effect, and will continue to optimize the process. Ultimately, the team plans to produce large area materials, which is also a feature of the process that was developed, and apply them to a spatial light modulator to develop applications such as spatial displays that can build huge three-dimensional images.

This work was financially supported by the Program for Fostering Globally Talented Researchers (R2802), JSPS. TG, YN, and MI acknowledge JSPS KAKENHI [Grant Nos. 17K19029, 16H04329, and 26220902]. TG acknowledges JST PRESTO [Grant No. JPMJPR1524]. FLD acknowledges the N2020; Nanotechnology based functional solutions (NORTE-45-2015-02).