Time has taught us that the states of matter that we know from high school (solid, liquid, gas and plasma) are just the tip of the iceberg. In the depths of quantum physics and magnetic materials, exotic phases are hidden that could revolutionize the technologies of the future. This is the case of the recent discovery by physicists Weiguo Yin e Alexei Tsvelik of the Brookhaven National Laboratory, who identified a new phase in a one-dimensional ferrimagnet: a state called “half ice, half fire.”
This extraordinary configuration consists of a pattern of electronic spins in which highly ordered states coexist (cold as ice) and highly disordered (hot as fire). The story of this discovery, published in the prestigious journal Physical Review Letters, is rooted in over a decade of research and represents a fundamental piece in the understanding of magnetic materials.
A little step back: what is a ferrimagnet in a few (and hopefully simple) words.
Imagine a tug-of-war team where 5 people are pulling on one side and 3 on the other. The rope will move toward the side with more people, but there will still be tension on both sides. The ferrimagnet is like that rope, it has a “net” magnetism even if the internal magnetic forces “counteract” each other a little.
In short: a ferrimagnet it is a material that, at a microscopic level, has atoms with magnetic moments aligned in opposite directions, ma moments in one direction are stronger than in the other.
A journey that began ten years ago
The discovery of this new phase of matter did not come out of nowhere. The journey began in 2012, when Yin and Tsvelik were part of a multi-institutional collaboration led by physicist John hill of Brookhaven Lab. The group was studying a magnetic compound called Sr3CuIrO6 (a material made from strontium, copper, iridium, and oxygen). That work also led to two publications in Physical Review Letters, one experimentally driven in 2012 and one theory-focused in 2013.
Despite their extensive research, however, something was still missing. As Tsvelik points out,
“Even after our extensive research, we still didn’t know how this state could be used.”
Ising’s mathematical model, which produced the “half-fire, half-ice” state, had been known for a century to not accommodate phase transitions at finite temperatures. Key pieces of the puzzle were missing.
Yin has recently identified a clue to the missing pieces. In two publications, he showed that the “forbidden” phase transition could be approached by an ultranarrow crossover phenomenon at a fixed finite temperature.
In even simpler words? Yin discovered that even if a transformation seems impossible, you can “trick” the system into taking place in a very specific and controlled way, at a certain temperature. It's like finding a secret passage from point A to point B, even if the direct route is blocked.
When Ice and Fire Switch Places
In their current research, Yin and Tsvelik found that “half fire, half ice” has a hidden, opposite state in which the hot and cold spins switch positions. In other words, the hot spins become cold and the cold spins become hot.
The model reveals that the transition between phases occurs in an extremely narrow temperature range, and the researchers have already suggested possible future applications. For example, this phenomenon of ultra-precise switching with a gigantic change in magnetic entropy could be useful for refrigeration technologies. It could also form the basis for a new type of quantum information storage technology in which the phases act as bits.
Ferrimagnet and “Half Ice, Half Fire” Phase: Implications and Future Prospects
The discovery of this new phase of matter is significant. Not only because it has never been observed before, but also because it is capable of driving extremely rapid phase switching in the material at a reasonable and finite temperature.
“Finding new states with exotic physical properties and being able to understand and control the transitions between those states are central problems in the fields of condensed matter physics and materials science,” Yin said.
“Solving these problems could lead to major advances in technologies such as quantum computing and spintronics.”
Tsvelik added:
“We suggest that our findings may open a new door to understanding and controlling phases and phase transitions in certain materials.”
The next step for researchers will be to explore the “fire-ice” phenomenon in systems with quantum spins and with additional lattice, charge and orbital degrees of freedom. As stated Yin, “the door to new possibilities is now wide open.”
It strikes me that this discovery is a perfect example of how surprising and unpredictable fundamental research can be. What began as the study of a simple one-dimensional model has revealed a physical phenomenon completely new, with potential applications ranging from energy technologies to quantum computing.
Sometimes, it is precisely in the simplest systems that nature's most fascinating complexities are hidden.
