Magnetoelectric coupling makes single-molecule magnets more "obedient"

Whether they carry a smart phone or a supercomputer deployed in the computer room, having more storage space and capacity is their common technical "dream". With the deepening of material research, single-molecule magnets have also emerged, and the use of single-molecule magnets as information storage units to achieve ultra-high-density information storage has also become the goal of scientists.

Since the first single-molecule magnet Mn12 was first discovered in 1993, the research on the magnetoelectric properties of single-molecule magnets has been continuously deepened. Recently, researchers from the Institute of Physics of the Chinese Academy of Sciences and Nankai University observed for the first time a significant magneto-dielectric effect in a single-molecule magnet containing rare-earth ion dysprosium (Dy). A few days ago, the reporter interviewed Dr. Wang Yuxia, one of the experimenters, the Department of Chemistry, Nankai University, and listened to her talk about how the electric field makes the single-molecule magnet "obedient" and the wonderful process of its magnetic regulation.

Big "belly volume"-with stronger data storage capacity

Single-molecule magnets are a type of special magnets composed of discrete, non-magnetically interacting nano-sized molecular units. Each molecule is an independent magnetic functional unit, which exhibits superparamagnetism at high temperatures and appears at low temperatures. Hysteresis and magnetization quantum tunneling behavior.

Wang Yuxia told the Sci-Tech Daily that the magnetism of ordinary magnets mainly comes from the magnetic interaction between adjacent paramagnetic centers. Nanomagnetic particles will produce some special quantum behavior due to their size. Single-molecule magnets can be switched between two states of "0" (molecular orientation in the direction of the magnetic field) and "1" (molecular orientation in the direction of the magnetic field) like a tiny magnet. "It is this characteristic that gives single-molecule magnets a large 'belly volume', which can greatly increase the information storage density, which means that the storage devices made of such magnets have stronger data storage capabilities." Wang Yuxia said, " Single-molecule magnet technology can store more than 200 megabits of data per square inch (6.45 square centimeters). If it is applied to quantum computers in the future, it is expected to achieve ultra-high density information storage. "

Have "personality"-maybe "lazy take a short cut" straight through

Magnetism and electricity are two basic properties of matter. As early as more than 100 years ago, Maxwell and other scientists unified magnetism and electricity under the framework of electrodynamics. Scientists have been working hard to explore the coupling of magnetism and electrical properties in solids. Regulation.

In the Book of Songs, there is a cloud that "throw me a papaya and report it to Qiongju". Scientists have always hoped that this "harmonic" electromagnetic coupling scene can also be seen on single-molecule magnets. Wang Yuxia told reporters that the magnetic behavior of single-molecule magnets is manifested by the slow magnetic relaxation of single molecules. "The so-called relaxation is simply time." Seeing the reporter's sorrowful face, Wang Yuxia explained by analogy: "It is like a person crossing mountains and over mountains, a single-molecule magnet exhibits magnetic behavior, and its electrons also have to pass through a high slope. "Climbing" to the other side usually takes a certain amount of time. This time is relaxation. "During the interview, the reporter learned that because of the higher energy levels of rare earth elements, the electrons of single-molecule magnets may" lazyly approach " "Straight through, so that the energy consumption from side to side is less, and the relaxation time is shorter. "These are not conducive to the expression of the magnetic properties of single-molecule magnets." Wang Yuxia said, "Our research hopes to better balance the" personality "of single-molecule magnets and achieve effective and reversible regulation of magnetic properties through electric fields."

The orderly controllability of this magnetoelectricity means high conversion efficiency and considerable application prospects. "For example, in the field of magnetic storage, magnetic records are fast to read but slow to write, and ferroelectric records are complex to read and write fast. If multiple ferromagnetic materials are used, it is possible to achieve ultra-high speed read and write processes at the same time." Wang Yuxia Said.

Broad prospects-storage density is hundreds of times higher than current technology

With the rapid development of wireless communication technology, information storage technology, electromagnetic interference technology and other fields, people have put forward higher requirements for the choice of materials and the miniaturization and integrated design of devices. The magnetoelectric heterostructure of the single-molecule magnet has many advantages such as free conversion of energy between the magnetic field and the electric field, and a large magnetoelectric conversion coefficient. Therefore, it has wide application prospects in sensors, multi-state memories, and radio-frequency microwave devices. In the interview, Wang Yuxia also revealed that they hope to use chemical synthesis to try to introduce ferroelectric polarization by breaking the space inversion symmetry, enhance the magnetoelectric coupling effect, and realize the regulation of the electric field on the magnetism or the magnetic field on the electrical properties. Novel magnetoelectric materials for the behavior of molecular magnets and ferroelectrics.

"Single-molecule magnets show that the magnetic memory effect is a necessary factor for all data storage. In theory, using single-molecule data storage can provide a data density that is one hundred times higher than current technology." Broad application prospects.

At present, the magnetic structure relationship of single-molecule magnets has been relatively clear. Wang Yuxia told reporters that the properties of single-molecule magnets can be preliminarily predicted based on the molecular configuration. If the molecule belongs to a symmetrical configuration with large magnetic anisotropy, it is more likely to become a single-molecule magnet. The reporter learned that in this experiment, Wang Yuxia and scientific research partners used the solution slow evaporation method to synthesize this rare earth dysprosium single molecular magnet single crystal sample, the size reached the order of millimeters. In this crystal, dysprosium ions with strong spin-orbit coupling are in a slightly distorted octahedral coordination field and have uniaxial anisotropy, which is conducive to the formation of single-molecule magnets. Through the measurement of AC magnetization and DC magnetization, the low-temperature magnetic relaxation behavior and magnetic anisotropy of the single-molecule magnet were determined. This research also laid a solid foundation for the follow-up electrical continuous measurement and observation. (Reporter Sun Yusong)