A collaborative team has developed a new way to create magnetic optical materials, one that removes a long-standing design bottleneck and could boost the speed and efficiency of data-center communications. Using an ion beam sputtering technique, the team fabricated nanoscale, labyrinth-like magnetic patterns that form reliably regardless of the underlying substrate strain.

The group comprised researchers from Tohoku University, Toyohashi University of Technology, Shin-Etsu Chemical Co., Ltd., and MIT.

Today's data centers depend on optical communications to shuttle enormous volumes of information, much like highways carrying constant streams of high-speed traffic. Magnetic garnet films, especially cerium-substituted yttrium iron garnet (Ce:YIG), act as the traffic signals and switches on these optical highways, ensuring information flows smoothly and in the right direction.

A key property for these components is perpendicular magnetic anisotropy, meaning the film's magnetization points straight "up" from the surface. However, until now, achieving this has been a delicate balancing act: researchers had to carefully match the crystal lattice of the film and the substrate. Think of it like carpeting a room. You need to cut the right amount of carpet to fit the room, otherwise the carpet will get strained if it is too big or too small. This requirement has severely limited material choices and design possibilities.

The team overcame this limitation by using ion beam sputtering to deposit Ce:YIG films onto two different substrates that applied opposite types of strain. Surprisingly, both films still displayed strong perpendicular magnetic anisotropy - even though their lattice mismatches (+0.38% and -0.12%) should have produced opposite outcomes.

The breakthrough came from uncovering the real driver of the films' magnetic behavior: magnetotaxial anisotropy, a growth-related effect that arises from how atoms arrange themselves during deposition. In simple terms, the film's atomic "scaffolding" determines the magnetic direction far more strongly than the stress from the underlying substrate - over ten times stronger, in fact.

The films also formed intricate, labyrinth-type magnetic domains only about 219 nm wide. For comparison, conventional domains are 10-100 micrometers wide, tens to hundreds of times larger. Shrinking these domains is like replacing bulky traffic lights with compact, ultra-responsive sensors, paving the way for faster and more efficient magneto-optical devices.

The material demonstrated a Faraday rotation of -1.05°/μm at a wavelength of 1064 nm, roughly 1.6 times better than conventional films. Its low saturation field (70 mT compared to 140-240 mT) means that smaller, energy-efficient magnets can be used to operate devices, reducing power consumption in large-scale systems.

"By achieving perpendicular magnetic anisotropy independent of substrate strain, we've removed a major design constraint," said Associate Professor Taichi Goto of Tohoku University. "This opens possibilities for integrating our magnetic optical materials with other spintronics materials and solid-state optical devices, enabling faster and more stable data communications in compact systems critical for data centers."

The findings, published in ACS Applied Optical Materials (November 25, 2025), could accelerate development of optical isolators for telecommunications, magneto-optical switches for data centers, and emerging spintronics applications.

Publication Details:

Title: Magnetotaxial Perpendicular Magnetic Anisotropy and Enhanced Faraday Rotation in Ion Beam Sputtered Cerium-Substituted Yttrium Iron Garnet

Authors: Taichi Goto, Takumi Koguchi, Yuki Yoshihara, Hibiki Miyashita, Kanta Mori, Toshiaki Watanabe, Allison C. Kaczmarek, Pang Boey Lim, Mitsuteru Inoue, Caroline A. Ross, Kazushi Ishiyama

Journal: ACS Applied Optical Materials

DOI: 10.1021/acsaom.5c00496