Researchers have identified a layered magnetic semiconductor that uniquely combines tunable electronic and magnetic properties, opening a new avenue for developing next-generation memory and logic chips. The material, known as chromium sulfide bromide (CrSBr), is a two-dimensional material that can be exfoliated into atomically thin layers, and its rare stability under normal environmental conditions makes it significantly easier to handle than other materials in its class.
This breakthrough is centered on the discovery that two distinct magnetic states, ferromagnetism and antiferromagnetism, can coexist and be controlled within the material. This duality allows for the creation of four-state logic devices, doubling the data storage potential compared to current two-state technologies. Such an advance could lead to ultra-powerful, compact computers and spintronic devices that store vast amounts of information in a small footprint while consuming less energy.
A Uniquely Stable 2D Magnet
Chromium sulfide bromide belongs to a class of substances called van der Waals crystals. These materials consist of layers that are held together by weak forces, allowing them to be peeled, or exfoliated, into 2D sheets just a few atoms thick. While many 2D magnets quickly degrade when exposed to oxygen and water, CrSBr is remarkably stable at ambient conditions, a feature that simplifies the fabrication of new devices for testing and application.
Furthermore, it maintains its magnetic properties at relatively high temperatures of around -223 to -280 degrees Fahrenheit. This avoids the need for expensive and cumbersome liquid helium cooling systems required by other quantum materials, which must be chilled to nearly -450 degrees Fahrenheit. According to researchers, the comparative ease of working with CrSBr allows them to fabricate and explore novel device structures and their properties more effectively.
Harnessing Dueling Magnetic Orders
The key to CrSBr’s potential lies in its complex magnetic behavior. Magnetism in materials is determined by the collective alignment of electron spins. In its ground state at low temperatures, CrSBr settles into an antiferromagnetic (AFM) arrangement. In this state, the magnetic moments of its electrons align in a regular, repeating pattern, but they alternate direction in each successive layer. However, researchers found that this material can also support ferromagnetism (FM), where electron spins align in the same direction.
The Role of Imperfections
A strong link between the material’s electrical behavior and its magnetism was discovered, largely due to naturally occurring defects in the crystal structure. These imperfections in the atomic layers create a useful coupling, allowing the magnetic state to be influenced by electrical inputs and also to be “read” by measuring the material’s electrical resistance. This provides a powerful, indirect method for observing the magnetic state, which is otherwise difficult to measure at such small scales.
A New Blueprint for Memory
This discovery has significant implications for the field of spin-electronics, or “spintronics,” which aims to use electron spin in addition to its charge to create more efficient electronics. The ability to control two coexisting magnetic states in CrSBr provides a new blueprint for memory technologies like magnetoresistive random-access memory (MRAM). Current MRAM devices store information in two states, a 0 or a 1, corresponding to two different magnetic orientations. By harnessing both the ferromagnetic and antiferromagnetic properties, CrSBr can be used to define four distinct, stable states. This could effectively double the storage density of memory chips without increasing their physical size.
The Quantum Potential of Excitons
Beyond memory, CrSBr shows promise for quantum computing, largely due to particles called excitons. An exciton is a quantum particle formed when an electron is energized and moves to a higher energy state, leaving a positively charged “hole” behind. The electron and hole remain bound together and can carry energy and information without an electrical charge.
Researchers discovered that the unique, layered magnetism of chromium sulfide bromide can confine these excitons to a single atomic layer, even within a larger, bulk piece of the material. This is a critical finding because it achieves the quantum behavior of a 2D material without the labor-intensive process of peeling off and stacking individual layers. This magnetic confinement offers a new method for controlling quantum information, potentially leading to quantum states that last longer and enable novel data processing techniques.
Collaborative Research and Future Paths
The research into CrSBr has been a collaborative effort involving scientists from several institutions, including Columbia University, Penn State, and the University of Michigan. Work conducted in the lab of chemist Xavier Roy at Columbia was foundational in creating and characterizing the material.
Looking ahead, researchers plan to experiment with growing CrSBr crystals with deliberate, engineered defects. By doing so, they hope to gain more precise control over the material’s coupled electronic and magnetic properties. The long-term vision is to build quantum machines that integrate all of the material’s unique characteristics. Such devices could use light to transfer information, electrons to process it, magnetism to store it, and atomic vibrations to modulate it, paving the way for a new generation of powerful and efficient technologies.
