As electronic devices keep evolving toward thinner, lighter, higher-efficiency and miniaturized designs, multiferroic materials possessing both magnetism and ferroelectricity have emerged as a major research hotspot. Leveraging the interplay between these two distinctive properties, such materials are expected to enable sensors with higher sensitivity and memory devices with faster read-write speeds.
Wei Suhuai, Chair Professor and Dean of the School of Physics, Division of Science at the Eastern Institute of Technology (EIT) in Ningbo, collaborated with Professor Lu Yunhao from Zhejiang University, Researcher Chen Lan from the Institute of Physics, Chinese Academy of Sciences, and Professor Yang Shengyuan from The Hong Kong Polytechnic University. They have achieved important progress in the research of two-dimensional room-temperature multiferroics and proposed a new strategy to realize multiferroicity via interlayer self-doping. The relevant findings were recently published in the top physics journal Physical Review Letters.
Research Background
Existing multiferroic materials are generally classified into two categories. In Type‑I multiferroics, ferroelectricity and magnetism originate from separate and independent sources. The two orders are not directly induced by each other, and their magnetoelectric coupling is typically linear yet weak.
In Type‑II multiferroics, ferroelectricity is a secondary induced order driven by primary magnetic ordering. This usually occurs in noncollinear magnetic structures, where the formation of magnetic ordering breaks symmetry and generates electric polarization. The magnetoelectric coupling mechanism in Type‑II multiferroics relies on spin‑orbit coupling, and their magnetoelectric coupling strength is generally higher than that of Type‑I, making them more suitable for practical applications.
Nevertheless, Type‑II multiferroics have critical drawbacks. First, since ferroelectricity is induced from magnetism via spin‑orbit coupling (which normally has a small energy scale), the ferroelectric order is usually weak with low transition temperatures, typically ranging from 10 to 50 K, far below room temperature. Second, the pool of stable Type‑II multiferroic materials remains very limited; the ordering in bulk multiferroic materials often cannot be preserved in ultrathin layers. These challenges impose substantial obstacles for material design and real‑world applications.
Research Highlights
In this work, the authors propose a design strategy for new multiferroic materials: interlayer self‑doped multiferroics. The study shows that owing to the preference of antiferromagnetic and ferromagnetic order for distinct band fillings, homogeneous bilayers with intermediate band filling exhibit intrinsic instability toward interlayer self‑doping. This results in antiferromagnetic order in one layer and ferromagnetic order in the other, accompanied by out‑of‑plane ferroelectricity.
Unlike conventional Type‑I and Type‑II multiferroics, the ferroelectric and magnetic orders in interlayer self‑doped multiferroics are inherently coupled and do not rely on spin‑orbit coupling, which endows them with the potential to persist at high temperatures. First‑principles calculations verified this mechanism in two specific systems: bilayer CrTe₂ and bilayer FeTe. Notably, multiferroicity in bilayer CrTe₂ is predicted to be stable at room temperature.
This study reveals a new class of multiferroic materials and opens a new route to design two‑dimensional ultrathin multiferroics with high transition temperatures and strong magnetoelectric response.
Zhong Shuling, a PhD student at Zhejiang University, is the first author of the paper. Yang Shengyuan, Chen Lan, Wei Suhuai and Lu Yunhao are the corresponding authors.
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