Zigzag arrangement of tiny magnets realizes nonreciprocal charge transport without external magnetic field

Deputy Director of Research Motoi Kimata at the Advanced Science Research Center, Nuclear Science Research Institute, Japan Atomic Energy Agency; Specially-Appointed Researcher Kenta Sudo at the Institute for Solid State Physics at the University of Tokyo; Assistant Professor Mitsuru Akaki at the Institute for Materials Research at Tohoku University (currently at the Research Facility Center for Science and Technology, Kobe University); and Associate Professor Hiroshi Tanida and Associate Professor Yuki Yanagi from the Liberal Arts and Sciences at Toyama Prefectural University discovered that in metals with a special structure where microscopic magnets (electron spins) are arranged in a zigzag pattern, a diode-like one-way electrical property (nonreciprocal charge transport) naturally appears, creating a bias in the direction in which electricity flows more easily. This was published in Physical Review Letters.

The research group focused on the compound NdRu₂Al₁₀, a neodymium-ruthenium-aluminum compound with a structure in which atoms are arranged in a zigzag pattern. At room temperature, the directions of electron spins are random, but when the temperature is lowered to 2.4 K, they exhibit antiferromagnetism, where the spin directions become opposite to each other. This spin arrangement forms an internal microscopic magnetic field, and it became clear that nonreciprocal charge transport appears as a result of this, creating a bias in the direction in which electricity flows more easily, even without applying an external magnetic field. Furthermore, it was found that this effect is more than 1,000 times stronger than that shown by conventional materials under external magnetic fields.

Moreover, when elongated microscopic samples of this crystal were fabricated using ion beam microfabrication technology and measured, it became clear that there are regions where the ordering of spin directions switches, and in those regions, the direction in which electricity flows more easily also reverses.

This achievement demonstrates a new principle in which the antiferromagnetic spin arrangement accompanying a zigzag atomic arrangement functions as an internal magnetic field, causing nonreciprocal charge transport that creates a bias in the direction in which electricity flows more easily, even without an external magnetic field. Application of this principle is expected to lead to the development of energy-efficient and ultra-compact next-generation devices.

Kimata commented: "This had been predicted theoretically, but we were able to demonstrate it. While the experimental results were at an extremely low temperature of 2.4 K, we also have prospects for materials that can exhibit the same effect at temperatures close to room temperature."

Journal Information
Publication: Physical Review Letters
Title: Large Spontaneous Nonreciprocal Charge Transport in a Zero-Magnetization Antiferromagnet
DOI: 10.1103/13pd-tlzp