Jawaharlal Nehru Centre for Advanced Scientific Research Scientists Uncover Unique Properties in Multiferroic Material Potential for Energy-Efficient Storage

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 storage.

3 distinct magnetic structures in magnetoelectric multiferroic material studied by JNCASR scientists at different temperatures.
(Image credit: Physical Review B)

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, chemistry and physics of materials unit, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), an autonomous institution under the Department of Science and 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, 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 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, 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. 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 storage by reducing energy consumption during writing processes. Additionally, these findings can be helpful for the development of 4-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.

Article: Successive ferroelectric transitions induced by complex spin structures in MnBi2S4

Physical Review B has published an article written by Pavitra N. Shanbhag, School of Advanced Materials, and Chemistry and Physics of Materials Unit, Jawaharlal Nehru Center for Advanced Scientific Research, Jakkur, Bangalore 560064, India, Fabio Orlandi, Pascal Manuel, ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom, Martin Etter, Shrikant Bhat, Deutsches Elektronen-Synchrotron (DESY), Hamburg 22607, Germany, and A. Sundaresan, School of Advanced Materials, and Chemistry and Physics of Materials Unit, Jawaharlal Nehru Center for Advanced Scientific Research, Jakkur, Bangalore 560064, India.

Abstract: “Our study reveals the emergence of ferroelectricity induced by incommensurate spin orders in the magnetic sulfide MnBi2S4, which has a HgBi2S4-type centrosymmetric monoclinic structure (C2/m). This compound reveals multiple magnetic transitions at TN1=27K, TN2=23K, and TN3=21.5K, associated with three distinct incommensurate spin structures (ICM1, ICM2, and ICM3). ICM1 is described as an antiferromagnetic spin density wave with an incommensurate modulation vector k1=(0,β,12) and magnetic superspace group C¯1.1′(α,β,γ)0s. While ICM2 has a similar propagation vector as ICM1, pyrocurrent measurements suggest the polar nature of this phase. This is further confirmed by neutron diffraction, which indicates a cycloidal structure with a magnetic superspace group Bm.1′(0,12,γ)0s. The magnetic ground state (ICM3) is a polar helical spin structure with magnetic space group B2.1′(0,0,γ)ss which is incommensurately modulated with propagation vector k2=(0,0,γ) where γ=0.3793(1) (at 1.5 K).“