Researchers at Dresden-Rossendorf-Helmholtzzentrum (HZDR) have identified a never-before-seen vibration pattern known as a Flocke state inside a very small magnetic vortex. In contrast to previous studies that relied on powerful laser pulses to generate these states, the Dresden team found that gentle stimulation using magnetic waves was sufficient. This discovery not only challenges existing concepts in fundamental physics, but could also serve as a kind of universal connector between electronics, spintronics, and quantum technology. The survey results are science.
Magnetic vortices form in ultrathin disks made of materials such as nickel-iron, and are often just micrometers or even nanometers in size. Inside these structures, tiny magnetic moments are arranged in a circular pattern, acting like the needles of a miniature compass. When disturbed, waves ripple through the system, much like a concerted “wave” of a stadium crowd. Each magnetic moment tilts slightly and transfers its motion to the next magnetic moment, creating a chain reaction. These collective wavelike excitations are known as magnons.
“These magnons can transmit information through the magnet without the need for charge transport,” explains Dr. Helmut Schultheis, project leader at the HZDR Institute for Ion Beam Physics and Materials. “This feature makes it very attractive for research into next-generation computing technologies.”
Unexpected frequency combs in small magnetic disks
The researchers were experimenting with particularly small magnetic disks, shrinking them from a few micrometers to just a few hundred nanometers. Their goal was to investigate how disk size affects neuromorphic computing, a brain-inspired approach to information processing. But while analyzing the data, they noticed something unusual. In some disks, instead of a single resonant signal, a series of closely spaced lines were produced, forming a so-called frequency comb.
“At first we thought it was a measurement artifact or some kind of interference,” Schultheis recalls. “But when we repeated the experiment, the effect appeared again. That’s when it became clear that we were looking at something truly new.”
Rotating vortex core drives new vibrational states
This explanation goes back to the work of French mathematician Gaston Floquet, who showed in the 19th century that systems exposed to periodic forces could generate entirely new vibrational states. Generating these frocket states typically requires large energy inputs, often delivered by powerful laser pulses.
In this case, the researchers discovered that magnetic vortices can spontaneously generate Flocke states when magnons are given enough energy. The magnon transfers some of its energy to the vortex core, causing it to move in a small circular path around its center. Even this small movement is enough to rhythmically change the magnetic state.
In experiments, this appears as a frequency comb. Instead of one sharp signal, multiple equally spaced lines appear, much like a pure tone is divided into harmonics. “We were stunned that such minute nuclear movements were enough to transform the familiar magnon spectrum into a variety of new states,” Schultheis says.
Ultra-low energy breakthrough with huge potential
One of the most impressive aspects of this discovery is how little energy is required. While previous methods relied on high-power lasers, this effect can be triggered with microwatts of power, far less than what a smartphone uses in standby mode.
This efficiency opens up new possibilities. Frequency combs generated in this way can help synchronize very disparate systems and connect ultrafast terahertz signals to classical electronics and quantum devices. “We call this a universal adapter,” Schultheis explains. “Just as a USB adapter allows devices with different connectors to work together, Floquet magnon can bridge incompatible frequencies.”
Towards future computing and quantum integration
The research team plans to investigate whether the same mechanism applies to other magnetic structures. This discovery could play an important role in the development of future computing systems by enabling communication between magnon-based signals, electronic circuits, and quantum components.
“On the one hand, our findings open up new avenues for tackling fundamental questions in magnetism,” Schultheis emphasizes. “On the other hand, it could ultimately serve as a valuable tool to interconnect the fields of electronics, spintronics, and quantum information technology.”
All measurements of magnetic vortices and analysis of data from multiple instruments were performed using the Labmule program developed at HZDR. The Labmule program can be used as a lab automation tool.
