By Jeannie Kever, University of Houston

The demands for data storage and processing have grown exponentially as the world becomes increasingly connected, emphasizing the need for new materials capable of more efficient data storage and data processing.

Researchers Liangzi Deng, left, and Paul Chu worked with colleagues reporting the discovery of a new compound capable of maintaining its skyrmion properties at room temperature through the use of high pressure. The work holds promise for next-generation data storage.

An international team of researchers, led by physicist Paul Ching-Wu Chu, founding director of the Texas Center for Superconductivity at the University of Houston, is reporting a new compound capable of maintaining its skyrmion properties at room temperature through the use of high pressure. The results also suggest the potential for using chemical pressure to maintain the properties at ambient pressure, offering promise for commercial applications.

The work is described in the Proceedings of the National Academy of Sciences.

A skyrmion is the smallest possible perturbation to a uniform magnet, a point-like region of reversed magnetization surrounded by a whirling twist of spins. These extremely small regions, along with the possibility of moving them using very little electrical current, make the materials hosting them promising candidates for high-density information storage. But the skyrmion state normally exists only at a very low and narrow temperature range. For example, in the compound Chu and colleagues studied, the skyrmion state normally exists only within a narrow temperature range of about 3 Kelvin degrees, between 55 K and 58.5 K (between -360.7 Fahrenheit and -354.4 Fahrenheit). That makes it impractical for most applications.

Working with a copper oxyselenide compound, Chu said the researchers were able to dramatically expand the temperature range at which the skyrmion state exists, up to to 300 degrees Kelvin, or about 80 degrees Fahrenheit, near room temperature. First author Liangzi Deng said they successfully detected the state at room temperature for the first time under 8 gigapascals, or GPa, of pressure, using a special technique he and colleagues developed. Deng is a researcher with the Texas Center for Superconductivity at UH (TcSUH).

Chu, the corresponding author for the work, said researchers also found that the copper oxyselenide compound undergoes different structural-phase transitions with increasing pressure, suggesting the possibility that the skyrmion state is more ubiquitous than previously thought.

“Our results suggest the insensitivity of the skyrmions to the underlying crystal lattices. More skyrmion material may be found in other compounds, as well,” Chu said.

The work suggests the pressure required to maintain the skyrmion state in the copper oxyselenide compound could be replicated chemically, allowing it to work under ambient pressure, another important requirement for potential commercial applications. That has some analogies to work Chu and his colleagues did with high-temperature superconductivity, announcing in 1987 that they had stabilized high-temperature superconductivity in YBCO (yttrium, barium, copper, and oxygen) by replacing ions in the compound with smaller isovalent ions.

In addition to Chu and Deng, researchers involved with the project include co-first author Hung-Cheng Wu, a visiting researcher at TcSUH from National Sun Yat-sen University in Taiwan; Alexander P. Litvinchuk and Rabin Dahal, both with TcSUH; Noah F. Q. Yuan of the Massachusetts Institute of Technology; Jey-Jau Lee of National Synchrotron Radiation Research Center in Taiwan; Helmuth Berger with the Institute of Physics of Complex Matter at the Ecole Polytechnique Federal de Lausanne in Switzerland; and Hung-Duen Yang with National Sun Yat-sen University.

Article: Room-temperature skyrmion phase in bulk Cu₂OSeO₃ under high pressures

Proceedings of the National Academy of Sciences has published an article written by Liangzi Deng, Texas Center for Superconductivity, University of Houston, Houston, TX 77204, and Department of Physics, University of Houston, Houston, TX 77204, Hung-Cheng Wu, Texas Center for Superconductivity, University of Houston, Houston, TX 77204, Department of Physics, University of Houston, Houston, TX 77204, and Department of Physics, National Sun Yat-sen University, 80424 Kaohsiung, Taiwan, Alexander P. Litvinchuk, Texas Center for Superconductivity, University of Houston, Houston, TX 77204, and Department of Physics, University of Houston, Houston, TX 77204, Noah F. Q. Yuan, Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, Jey-Jau Lee, National Synchrotron Radiation Research Center, 30076 Hsinchu, Taiwan, Rabin Dahal, Texas Center for Superconductivity, University of Houston, Houston, TX 77204, and Department of Physics, University of Houston, Houston, TX 77204, Helmuth Berger, Institute of Physics of Complex Matter, Ecole Polytechnique Federal de Lausanne, CH-1015 Lausanne, Switzerland, Hung-Duen Yang, Department of Physics, National Sun Yat-sen University, 80424 Kaohsiung, Taiwan, and Center of Crystal Research, National Sun Yat-sen University, 80424 Kaohsiung, Taiwan, and Ching-Wu Chu, Texas Center for Superconductivity, University of Houston, Houston, TX 77204, Department of Physics, University of Houston, Houston, TX 77204, and Lawrence Berkeley National Laboratory, Berkeley, CA 94720.

Abstract: “A skyrmion state in a noncentrosymmetric helimagnet displays topologically protected spin textures with profound technological implications for high-density information storage, ultrafast spintronics, and effective microwave devices. Usually, its equilibrium state in a bulk helimagnet occurs only over a very restricted magnetic field–temperature phase space and often in the low-temperature region near the magnetic transition temperature T_c. We have expanded and enhanced the skyrmion phase region from the small range of 55 to 58.5 K to 5 to 300 K in single-crystalline Cu₂OSeO₃ by pressures up to 42.1 GPa through a series of phase transitions from the cubic P2₁3, through orthorhombic P2₁2₁2₁ and monoclinic P2₁, and finally to the triclinic P1 phase, using our newly developed ultrasensitive high-pressure magnetization technique. The results are in agreement with our Ginzburg–Landau free energy analyses, showing that pressures tend to stabilize the skyrmion states and at higher temperatures. The observations also indicate that the skyrmion state can be achieved at higher temperatures in various crystal symmetries, suggesting the insensitivity of skyrmions to the underlying crystal lattices and thus the possible more ubiquitous presence of skyrmions in helimagnets.“