Working at nanoscale dimensions, a team of scientists led by the Department of Energy’s Oak Ridge National Laboratory revealed a new way to measure high-speed fluctuations in magnetic materials. Knowledge obtained by these new measurements, published in Nano Letters, could be used to advance technologies ranging from traditional computing to the emerging field of quantum computing.
Many materials undergo phase transitions characterized by temperature-dependent stepwise changes of important fundamental properties. Understanding materials’ behavior near a critical transition temperature is key to developing new technologies that take advantage of unique physical properties.
In this study, the team used a nanoscale quantum sensor to measure spin fluctuations near a phase transition in a magnetic thin film. Thin films with magnetic properties at room temperature are essential for data storage, sensors and electronic devices because their magnetic properties can be precisely controlled and manipulated.
The team used a specialized instrument called a scanning nitrogen-vacancy center microscope at the Center for Nanophase Materials Sciences, a DOE Office of Science user facility at ORNL. A nitrogen-vacancy center is an atomic-scale defect in diamond where a nitrogen atom takes the place of a carbon atom, and a neighboring carbon atom is missing, creating a special configuration of quantum spin states. In a nitrogen-vacancy center microscope, the defect reacts to static and fluctuating magnetic fields, allowing scientists to detect signals on a single spin level to examine nanoscale structures.
“The nitrogen-vacancy center functions as both a quantum bit, or qubit, and a highly sensitive sensor that we moved around on top of the thin film to measure temperature-dependent changes in magnetic properties and spin fluctuations that cannot be measured any other way,” said ORNL’s Ben Lawrie, a research scientist in ORNL’s Materials Science and Technology Division.
Spin fluctuations are observed when the magnetic properties of a material governed by the spin orientation keep changing direction rather than staying fixed. The team measured the spin fluctuations as the thin film went through a phase transition between different magnetic states that was induced by changing the sample temperature.
These measurements revealed how local changes in spin fluctuations are linked together globally near phase transitions. This nanoscale understanding of interacting spins could lead to new spin-based information-processing technologies and deeper insights into wide classes of quantum materials.
“Advances in spintronics will improve digital storage and computing efficiency. Meanwhile, spin-based quantum computing offers the tantalizing promise of classically inaccessible simulation if we can learn to control interactions between spins and their environment,” Lawrie said.
This type of research bridges ORNL’s capabilities in quantum information and condensed matter physics. “If we can use today’s generation of quantum resources to gain new understanding of classical and quantum states in materials, that will help us to design new quantum devices with applications in networking, sensing and computing,” Lawrie said.
