Half ice, half fire: The bizarre new magnetic spin state

Scientists recently spotted a peculiar new magnetic spin phase that defies conventional thinking. It merges highly ordered and significantly disordered electron spins in the same lattice, which experts are calling the half-ice, half-fire state.

This unique combination surfaced in a one-dimensional model, where many had assumed such dramatic spin transformations could never emerge. It forces a rethink of our understanding of magnetism, hinting at fresh ways to manage and manipulate these atomic-scale magnets.

These insights come from physicists Weiguo Yin and Alexei Tsvelik, who both work at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory.

The experts noticed that the system’s so-called hot spins, which tend to fluctuate, swapped roles with the so-called cold spins, which normally remain rigid and aligned.

Magnetic spin roles switch with heat

The phenomenon shares roots with an earlier discovery called “half fire, half ice,” which was first recorded in 2016. In that earlier scenario, the hot region resided on one sublattice, while the cold region took hold on another.

In the new half-ice, half-fire phase, these assignments flip, creating a starkly different magnetic profile. The switch highlights how small temperature adjustments might ignite abrupt changes in spin order, even in low-dimensional systems once thought immune to such transformations.

Much of this hinges on the ferrimagnet involved, a material with sublattices that carry unequal magnetic moments.

Unlike a ferromagnet, where all spins align in one direction, or an antiferromagnet, where spins alternate in sign, a ferrimagnet possesses a net magnetization, but not every spin is identical.

Why magnetic spins matter

Electron spins act like tiny bar magnets, each pointing in an up or down orientation. Their collective behavior sets the stage for everything from magnetic tapes to advanced sensors.

Engineers leverage this property in spintronics, a branch of electronics that exploits spin rather than just electric charge. By controlling how spins align, devices can become faster and less power-hungry than traditional semiconductor-based electronics.

Some researchers even look to quantum computing, where the superposition of spins can store vast amounts of data more efficiently than conventional bits. These systems often require delicate temperature conditions, so finding a stable phase transition at moderate heat levels could be a game-changer.

A narrow window for change

One striking aspect of half ice, half fire is its ultrasharp transition at a practical temperature. Many one-dimensional spin models never show phase transitions at finite temperature, which makes this discovery particularly surprising.

In simple terms, the spins reorganize in a near-instant flip when certain thermal energy levels are reached. This abrupt realignment points to hidden pathways in magnetic materials that standard theories do not fully address.

This quick switch correlates with a sudden rearrangement of entropy, the formal measure of disorder within a system. Minor thermal inputs can shift the balance between hot and cold spins, marking a borderline between two distinctly ordered magnetic states.

Such an entropy-driven flip could fuel innovations in refrigeration technology by exploiting a magnetocaloric effect. That effect involves adjusting magnetic fields or temperatures to produce cooling, which offers a greener alternative to conventional compressors that rely on chemical refrigerants.

Implications for information storage

Data storage often hinges on how easily a magnetic domain can be switched. If half ice, half fire permits quick toggling with minimal energy, it could serve as a candidate for next-generation memory elements.

During a normal write operation, devices expend energy flipping magnetic bits on and off. If a system can trigger a flip through a tiny thermal or field tweak, it might enable high-density memories that run cooler and last longer.

“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,” said Yin. 

“We suggest that our findings may open a new door to understanding and controlling phases and phase transitions in certain materials,” said Tsvelik.

Experts hope to dig deeper into the role of lattice distortions, electric charge, and orbital influences in shaping this phenomenon. Future studies may reveal new angles on how spins behave under competing forces, which would open doors to fresh perspectives in magnetic research.

Some anticipate that quantum effects might further complicate the picture in other, low-dimensional magnets. Whether these effects create additional half ice, half fire states or unlock as yet unknown phenomena remains to be seen.

The study is published in Physical Review Letters.

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