AUSTIN, Texas — For decades, scientists have been studying a group of unusual materials called multiferroics that could be useful for a range of applications including computer memory, chemical sensors, and quantum computers. In a study published in Nature, researchers from The University of Texas at Austin and the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) demonstrated that the layered multiferroic material nickel iodide (NiI2) may be the best candidate yet for devices that are extremely fast and compact.
Multiferroics have a special property called magnetoelectric coupling, which means that you can manipulate magnetic properties of the material with an electric field and vice versa, electric properties with magnetic fields. The researchers found NiI2 has greater magnetoelectric coupling than any known material of its kind, making it a prime candidate for technology advances.
“Unveiling these effects at the scale of atomically thin nickel iodide flakes was a formidable challenge,” said Frank Gao, a postdoctoral fellow in physics at UT and co-lead author of the paper, “but our success presents a significant advancement in the field of multiferroics.”
“Our discovery paves the way for extremely fast and energy-efficient magnetoelectric devices, including magnetic memories,” added graduate student Xinyue Peng, the project’s other co-lead author.
Electric and magnetic fields are fundamental for our understanding of the world and for modern technologies. Inside a material, electric charges and atomic magnetic moments may order themselves in such a way that their properties add up, forming an electric polarization or a magnetization. Such materials are known as ferroelectrics or ferromagnets depending on which of these quantities is in an ordered state.
However, in exotic materials like multiferroics, such electric and magnetic orders co-exist. The magnetic and electric orders can be entangled so that a change in one causes a change in the other. This property makes these materials attractive candidates for faster, smaller, and more efficient devices. For such devices to work effectively, it is important to find materials with particularly strong magnetoelectric coupling as described by the research team with NiI2 in their study.
The researchers accomplished this by exciting the material with ultrashort laser pulses in the femtosecond range (a millionth of a billionth of a second) and then tracking changes in its electric and magnetic orders via their impact on specific optical properties.
When researchers irradiate a thin layer of nickel iodide with an ultrafast laser pulse, corkscrew-shaped features called “chiral helical magnetoelectric oscillations” arise. These features could be useful for applications including fast compact computer memories. To understand why magnetoelectric coupling is stronger in NiI2 than similar materials, extensive calculations were performed.
“Two factors play important roles here,” said co-author Emil Viñas Boström from MPSD. “One is strong coupling between electrons’ spin and orbital motion on iodine atoms — known as spin-orbit coupling. The second factor is the particular form of magnetic order in nickel iodide known as spin spiral or spin helix.”
Materials like NiI2 with large magnetoelectric coupling have potential applications according to researchers: compact energy-efficient magnetic computer memory; interconnects in quantum computing platforms; chemical sensors ensuring quality control; drug safety within chemical/pharmaceutical industries.
Researchers hope these insights will identify other materials with similar properties while engineering techniques might enhance NiI2's magnetoelectric coupling further.
This work was conceived/supervised by Edoardo Baldini assistant professor physics UT Angel Rubio director MPSD.
Other UT authors include Dong Seob Kim Xiaoqin Li.
Other MPSD authors include Xinle Cheng Peizhe Tang.
Additional authors Ravish K Jain Deepak Vishnu Kalaivanan Raju Raman Sankar Shang-Fan Lee Academia Sinica Michael A Sentef University Bremen Takashi Kurumaji California Institute Technology
Funding provided Robert A Welch Foundation US National Science Foundation US Air Force Office Scientific Research European Union Horizon Europe research innovation program Cluster Excellence CUI Advanced Imaging Matter Grupos Consolidados Max Planck-New York City Center Non-Equilibrium Quantum Phenomena Simons Foundation Ministry Science Technology Taiwan