Researchers have identified a unique mechanism of electric polarization via magnetic ordering in a novel mineral named “MnBi2S4”, which can be useful for energy efficient data storage.
Magnetoelectric multiferroics are a special class of materials popular among the research fraternity for their rarity and unique properties. Interestingly, these materials can exhibit both magnetism and ferroelectricity simultaneously. This dual property is particularly fascinating, as materials typically possess either magnetism or ferroelectricity. Finding a single material with both these properties, is therefore, rare and valuable, especially for advanced technology applications like spintronics, electronic memory devices, and other electronic components like actuators and switches.
In recent times, the research fraternity has been particularly interested in a particular type of multiferroic called “spin-driven multiferroics”. These spin-driven multiferroic materials exhibit ferroelectricity only when specific magnetic structures are present. This discovery has sparked a lot of interest in finding out new materials with different types of magnetism for various applications.
Now advancing research, Professor A. Sundaresan, Chair of the Chemistry & Physics of Materials Unit at Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), an autonomous institution under the Department of Science & Technology (DST), Govt. of India. has made a groundbreaking discovery in the field of magnetoelectric materials. The findings of his study are outlined in a recent paper published in the journal PHYSICAL REVIEW B. The study focuses on a novel material named “MnBi2S4”, which exhibits a unique mechanism of inducing electric polarization via magnetic ordering.
MnBi2S4 is also known as mineral graţianite and belongs to the ternary manganese chalcogenide family. On conducting a detailed study using high-resolution neutron diffraction, Prof. Sundaresan’s team identified distinct magnetic structures in the material, including a spin density wave, as well as cycloidal and helical spin structures. Importantly, they found that the last two spin structures induce ferroelectricity in the material.
In contrast to a previous paper that explored the combined effect of polar structure resulting from chemical ordering and the magnetic structure for magnetoelectric coupling, this study by Prof. Sundaresan reveals that MnBi2S4, also known to be centrosymmetric, undergoes magnetic ordering at low temperatures (27, 23, and 21.5 Kelvins). Neutron diffraction was crucial in characterizing the different magnetic structures responsible for electric polarization at these temperatures.
At 27 Kelvin, the researchers observed a spin density wave structure, which did not break inversion symmetry nor induced polarization. However, as the temperature decreased to 23 Kelvin, a magnetic transition occurred, resulting in a cycloidal spin structure that did break inversion symmetry and induced polarization. Further cooling to 21.5 Kelvin led to a helical structure, also breaking inversion symmetry and inducing polarization.
Explaining further, Prof. Sundaresan says, “The significance of this finding lies in the strong coupling between magnetism and electric polarization. The unique mechanism, driven by magnetic frustration, represents a breakthrough in magnetoelectric coupling.” Adding further, he says, “This discovery is particularly important as it has never been reported in the specific MnBi2S4 material before.”
The findings of this study could find applicability in the domain of energy-efficient data storage. Specifically, if the material possesses the ability to exhibit the same phenomena at room temperature, it could pave the way for energy-efficient manipulation of spin using small electric fields. This, in turn, could revolutionize data storage by reducing energy consumption during writing processes. Additionally, these findings can be helpful for the development of four-state logic memory system, providing additional degrees of freedom for device performance compared to the current binary logic systems. Going ahead, however, the researchers express the need for further exploration of different materials and structures to understand the mechanisms that break inversion symmetry and induce polarization, with the goal of finding materials that exhibit these properties at room temperature.
For this research, Sheikh Saqr Laboratory and International Centre for Materials Science at Jawaharlal Nehru Centre for Advanced Scientific Research provided experimental facilities, and DST, SERB, and the Government of India provided financial support. The Science and Technology Facility Council (STFC UK) provided neutron beam time.
Publication link: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.109.024401
