HMN 2025: How Mirror symmetry prompts ultralow magnetic damping in 2D van der Waals ferromagnets

Two-dimensional (2D) van der Waals (vdW) ferromagnets are thin and magnetic materials in which molecules or layers are held together by weak attractive forces known as vdW forces. These materials have proved to be promising for the development of spintronic devices, systems that operate leveraging the spin (i.e., intrinsic angular momentum) of electrons, as opposed to electric charge.

A crucial parameter in the context of magnetization is the so-called Gilbert damping coefficient, which indicates how quickly a material’s magnetization loses energy and returns to a state of equilibrium after being disturbed. A lower damping coefficient is more favorable for the development of spintronics, as it means that less energy is lost once a material’s magnetization is set into motion.

Researchers at Beijing Normal University, Shanghai University and Fudan University carried out a study aimed at better understanding the underpinnings of low Gilbert damping in 2D vdW ferromagnets.

Their paper, published in Physical Review Letters, suggests that mirror symmetry in these atomically thin materials blocks intraband transitions, which in turn yields ultralow magnetic damping.

“This work began with a simple but profound question that had been on my mind for years: Do 2D vdW magnets possess any unique physical properties that distinguish them from conventional three-dimensional (3D) magnets—and could these properties substantially improve high-performance, low-power magnetic memory or computing devices?” Zhe Yuan, co-author of the paper, told Phys.org.

The roots of the team’s study

A key advantage of 2D vdW ferromagnets is that they retain magnetism down to a single atomically thin layer. Concurrently, their layered but thin structure significantly alters the behavior of electrons, prompting the emergence of phenomena that are not observed in bulk magnetic materials.

“My collaborators and I have been studying Gilbert damping for over a decade, because it plays a central role in magnetization dynamics,” said Yuan.

“Much like viscosity determines how quickly an oscillating spring comes to rest, Gilbert damping governs how fast magnetization relaxes to equilibrium. It is also a key factor in the energy efficiency of spintronic devices, so finding materials with ultralow damping has been a long-standing goal in the field.”

In conventional ferromagnets, damping is always associated with a conductivity-like component emerging from intraband electronic transitions and a resistivity-like component derived from interband transitions. As the temperature rises, the first of these components becomes less prominent, while the second becomes more prominent.

“This competition produces a nonmonotonic temperature dependence and sets a practical lower limit for damping—it cannot be reduced beyond that threshold,” said Yuan.

“To our surprise, we found that in certain 2D vdW ferromagnets, such as Fe₃GeTe₂ and Fe₃GaTe₂, the intraband contribution completely vanishes due to symmetry, leaving only the interband part. This results in a purely monotonic temperature dependence and suggests that the damping can, in principle, become arbitrarily small as the material quality improves. That exciting realization drove us to investigate the phenomenon in depth.”

Exploring ultralow damping in 2D vdW ferromagnets

The primary goal of the researchers’ recent study was to shed new light on the microscopic origin of the behavior that they previously observed in some 2D vdW ferromagnets. To do this, they performed first-principle electronic structure calculations and tried to connect the electronic structure of the 2D magnets to the damping using a theoretical method known as a so-called torque-correlation framework.

Using these methods, the researchers were able to demonstrate the influence of crystal symmetry, magnetization direction, layer stacking and band topology on the magnets’ damping. They found that mirror symmetry prevents intraband transitions, which in turn enables Gilbert damping with no fundamental lower limit.

“We combined density-functional theory calculations with a torque-correlation formalism—a well-established first-principles approach for intrinsic damping—to compute the contribution of spin-orbit coupling near the Fermi surface,” explained Yuan.

“Temperature and disorder effects were included through a scattering-rate parameter in the spectral functions. This theoretical formalism allowed us to separate the intraband and interband contributions explicitly.”

The crystal structure of some monolayer and few-layer vdW magnets follows a so-called mirror symmetry. The team showed that when the magnetization of these magnets is perpendicular to the plane, their crystal structure’s mirror symmetry forbids intraband transitions that typically prompt conductivity-like damping.

“This removes the conventional lower bound on damping, allowing it to reach ultralow values ( in our calculations) under clean conditions,” said Yuan.

“Importantly, this is the first theoretical work to establish a clear, quantitative link between the symmetry of a magnetic system and the magnitude of its Gilbert damping. It also provides a practical design rule: by controlling symmetry—through magnetization direction, layer stacking, or structural modifications—one can systematically tune the damping strength.”

Informing the development of spintronics

This study opens new possibilities for identifying and designing 2D vdW ferromagnets with intrinsically ultralow Gilbert damping coefficients. It also shows that the mirror symmetry of 2D vdW ferromagnets plays a crucial role in enabling this ultralow magnetic damping.

“We also showed that when mirror symmetry is broken by tilting the magnetization, the intraband channel re-emerges, causing the damping to increase dramatically,” said Yuan.

“This symmetry-controlled anisotropy offers a powerful new way to tune damping without introducing material disorder, and it provides a clear experimental signature for verifying our predictions.”

The results gathered by Yuan and his colleagues could have important implications for the development of spintronic devices. By guiding the design of 2D vdW magnets with symmetry-suppressed damping, the work could enable the introduction of more advanced spintronic systems that are faster, more energy-efficient and compatible with existing nanoelectronic components.

“Following this work, we are pursuing two main research directions,” said Yuan. “The first is to explore other symmetry-governed phenomena. We aim to study how symmetry influences other key properties, such as electrical resistivity and spin-charge conversion, which are also central to spintronic applications.”

The researchers are now also planning to extend their analyses to also include vdW magnetic insulators. These are layered materials held together by vdW forces that do not conduct electricity.

“Many vdW magnetic materials are semiconductors or insulators without conduction electrons at the Fermi level,” added Yuan.

“In these systems, magnetization damping arises from magnon-magnon and magnon-phonon interactions rather than electronic transitions. We plan to develop new theoretical frameworks to describe these mechanisms quantitatively, to build a unified understanding of damping across all classes of magnetic materials.”

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