There is growing demand for ‘smart’ materials that can change their physical properties in response to various external stimuli such as light, heat, pressure, magnetic and electric fields. One such physical property is the magnetic state of material complexes, which depends on electronic spin states. Metal atoms in these complexes can change their spin state – between magnetic and non-magnetic configurations – in response to light, heat, or mechanical pressure.
In two new studies, Abhishek Mondal, Associate Professor at the Solid State and Structural Chemistry Unit (SSCU), Indian Institute of Science (IISc), and his team report the synthesis of novel chemical frameworks – highly porous crystals made from self-assembling metal-organic layers – capable of reversible magnetic switching. These materials can form the building blocks for next-generation data storage units, quantum processors, and advanced industrial sensors.
The first study, published in Angewandte Chemie, solves a long-standing challenge in materials science: achieving robust magnetic switching in 3D beehive-type porous materials typically used for gas or liquid sensing. When a target gas or liquid enters or leaves the material, the crystal lattice in the material expands or contracts, stimulating the atoms to switch their magnetic state. In traditional porous materials, however, this expansion/contraction is limited because the push/pull force exerted by an atom within the lattice on its neighbours is absorbed by the pores and restricted to the vicinity of that atom. This limits the efficiency of these sensors because the material does not switch states as a whole.
To overcome this challenge, Mondal and his team designed a new chemical complex that is not only highly porous but also has an elastic matrix. When each atom in this matrix switches spin states, its push against neighbours propagates seamlessly through the elastic lattice, prompting a domino effect that causes the entire material to neatly flip its magnetic state – a phenomenon known as “cooperative behaviour”. Crucially, this magnetic transition is completely reversible, enabling the reuse of these materials. In addition to mechanical pressure, light and heat can also stimulate the spin state switch reversibly.
“We are currently working on scaling up the complex to design smart gas-capture sensors that can selectively adsorb industrially critical gases like CH4, CO and CO2 with supreme sensitivity,” says Mondal.
Although such materials can be highly useful for environmental and biological sensing, a major bottleneck has been the temperature at which they can operate. “Our goal was to synthesise a chemical system that exhibits these transitions near ambient temperatures,” explains Krishna Kaushik, PhD student at SSCU and first author of both studies. “Contemporary materials often operate only at ultra-low temperatures below 50 K (-223°C). They are highly volatile and relax back to their ground state with even a slight rise in temperature.” Maintaining such extremely cold environments requires energy-intensive and expensive cooling systems.
To address this limitation, in another study published in Small, the team designed a 2D hexagonal framework that achieves light-, heat- and solvent-induced magnetic transitions near ambient temperatures. The researchers first synthesised a precursor complex that, when left in its solution, reacts with the surrounding solvent molecules and atmospheric moisture to transform into a new, highly stable complex. While the initial network switches spin and electronic states at a chilly temperature of 176 K (around -97°C), the transformed complex remarkably exhibits two distinct transitions at around 240 K and 310 K (around -33°C and 37°C), successfully bringing magnetic switching into the room-temperature domain. The switch is also accompanied by a vivid change in colour, offering a striking visual fingerprint of the transformation that can be tracked directly by the human eye.
Beyond sensing applications, these switchable materials offer exciting opportunities for future quantum technologies. The materials can reversibly change between two magnetic states when exposed to light, heat, or pressure, much like a tiny molecular switch. This ability to control magnetic states at the atomic level is important because it mirrors the fundamental principle behind quantum technologies, where information can be stored and manipulated in entirely new ways. While practical quantum computers are still under development, discoveries such as these provide important building blocks for the next generation of advanced computing, communication, and sensing technologies.
“Although these discoveries are still at the fundamental research stage, they address important global challenges,” says Mondal. “Modern data centres and electronic devices consume enormous amounts of energy. Developing alternative materials that operate more efficiently could reduce energy demands and contribute to more sustainable technologies. Similarly, materials capable of acting simultaneously as sensors, switches, and memory elements may simplify device architectures and reduce manufacturing costs.”
-Rashmi Kumari
