This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Multiferroics are materials that simultaneously exhibit two or more ferroic orders—stable arrangements of physical properties that can be switched using an external stimulus. These materials could be highly advantageous for the development of various technologies, including non-volatile, low-power memory devices, spintronic devices, miniaturized electronics, neuromorphic hardware, sensors and magnetoelectric devices.
The key advantage of multiferroics is that their different ferroic orders can be coupled, for instance allowing engineers to alter magnetic behavior using an electric voltage. Despite their promise, synthesizing multiferroics that are stable, ultrathin and controllable at room temperature has so far proved challenging. Researchers at the University of Maryland and other institutes recently demonstrated an approach for creating van der Waals heterostructures that exhibit multiferroicity at room temperature.
Their strategy, outlined in a paper published in Science, was successfully used to create a 2D multiferroic heterostructure in which magnetic properties can be tuned using small voltages. "Long-range ferroic orders (such as ferromagnetic order and ferroelectric order) are not easy to be achieved in 2D systems," Cheng Gong, senior author of the paper, told Phys.org. "Integrating several orders together in a 2D system is even harder.
Realizing multiple ferroic orders in a 2D system, under the threat of thermal agitations at room temperature, is imaginably challenging. However, once achieved, the reward would be big." Controlling ferroic orders in 2D materials is a long-standing goal for materials scientists. Gong and his colleagues have been working towards this goal for several years.
"Enforcing two or more ferroic orders into a simple material is not easy, as different ferroic orders have different opponents for their survival in 2D systems," explained Gong. "Our approach is to realize 2D ferromagnetic order and 2D ferroelectric order in two separate 2D layers and then merge them together to form a heterostructure." Gong and his colleagues used their approach to create a heterostructure that combines ferromagnetic triiron gallium ditelluride (Fe₃GaTe₂) with ferroelectric copper indium thiophosphate (CuInP₂S₆). First, they produced thin flakes of these two materials by mechanically separating them from larger crystals.
They then placed the ferroelectric CuInP₂S₆ flakes on top of the ferromagnetic Fe₃GaTe₂ flakes, creating a vertically stacked van der Waals heterostructure. Finally, they added transparent indium tin oxide (ITO) and metallic chromium–gold (Cr/Au) electrodes that could be used to apply voltages across the heterostructure. "The obvious advantage of our approach is that it breaks down the challenge of realizing a few different orders in one single-phase material," said Gong.
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