MIT physicists used a terahertz laser, a light source that oscillates more than 1 trillion times per second, to directly stimulate the atoms of an antiferromagnetic material. Their results are attracting attention because they provide new ways to control and switch antiferromagnetic materials and have the potential to advance information processing and memory chip technology.
Iliad others. demonstrated efficient manipulation of the magnetic ground state of layered magnets by a non-thermal route using terahertz light, and observed enhanced variations in order parameters as a promising area for exploring metastable hidden quantum states. The region near the critical point was established. Image credit: Adam Glanzman.
In a common magnet, known as a ferromagnetic material, the spins of the atoms point in the same direction, making the whole magnet susceptible to the influence of an external magnetic field and drawn in that direction.
In contrast, antiferromagnets are composed of atoms with alternating spins, with each atom pointing in the opposite direction from its neighbor.
This top, bottom, top, bottom order basically cancels out the spinout and gives the antiferromagnet a net zero magnetization that is unaffected by magnetic forces.
If memory chips could be made of antiferromagnetic materials, it would be possible to “write'' data into minute regions of the material called domains.
A certain configuration of spin orientation in a particular region (e.g., up-down) represents a classical bit ‘0’, and a different configuration (down-up) means ‘1’. Data written on such chips becomes robust against external magnetic influences.
For this reason, scientists believe that antiferromagnetic materials could provide a more robust alternative to existing magnetic-based storage technologies.
However, a major hurdle has been how to control antiferromagnets in a way that reliably switches the material from one magnetic state to another.
MIT professor Nuh Gedik and his colleagues were able to controllably switch antiferromagnets into new magnetic states using carefully tuned terahertz light.
“Antiferromagnetic materials are robust and unaffected by unwanted stray magnetic fields,” Professor Gedick said.
“But this robustness is also a double-edged sword: their insensitivity to weak magnetic fields makes these materials difficult to control.”
Researchers collaborated with FePS3a material that transitions to an antiferromagnetic phase at a critical temperature of about 118 K.
They thought that by tuning in to the vibrations of atoms, it might be possible to control the transitions of matter.
“You can imagine that any solid material has a periodic arrangement of different atoms, with little springs between them,'' said Dr. Alexander von Hogen of MIT.
“When you pull one atom, it vibrates at a unique frequency that typically occurs in the terahertz range.”
The way atoms vibrate is also related to how their spins interact.
Scientists believe that if they can stimulate atoms with a terahertz source called phonons, which vibrate at the same frequency as the atoms' collective vibrations, the effect will change the spins of the atoms from a perfectly balanced magnetically staggered state. It was inferred that there was a possibility of deviation.
When the balance is disrupted, the atoms have more spin in one direction than the other, creating a preferred orientation that moves the essentially unmagnetized material into a new magnetic state with finite magnetization.
“The idea is to kill two birds with one stone: we excite terahertz vibrations in atoms, which are also coupled to their spins,” Professor Gedick said.
To test this idea, they placed a sample of FePS.3 It was cooled to a temperature below 118K in a vacuum chamber.
They then generated terahertz pulses by directing a beam of near-infrared light at an organic crystal, converting the light to terahertz frequencies.
This terahertz light was then directed at the sample.
“This terahertz pulse is what is used to induce changes in the sample,” said Dr. Tianchuang Luo of MIT.
“It’s like ‘writing’ a new state to the sample.”
To confirm that the pulse caused a change in the material’s magnetism, the authors also aimed two near-infrared lasers, each with opposite circular polarization, at the sample.
Without the influence of the terahertz pulse, there should be no difference in the intensity of the transmitted infrared laser.
“Just seeing the differences tells us that the material is no longer the original antiferromagnetic material, but is essentially inducing a new magnetic state by shaking the atoms using terahertz light,” MIT said Dr. Bateer Ilyas.
Through repeated experiments, the researchers observed that the terahertz pulses were able to successfully switch previously antiferromagnetic materials into a new magnetic state. This transition persisted for a surprisingly long time, more than a few milliseconds, even after the laser was turned off.
“People have observed such light-induced phase transitions in other systems before, but typically their survival times are very short, on the order of picoseconds, or trillionths of a second. ,” Professor Gedick said.
of study Published in a magazine nature.
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B. Ilyas others. 2024. Near-critical terahertz field-induced metastable magnetization in FePS3. nature 636, 609-614; doi: 10.1038/s41586-024-08226-x
This article is a version of a press release provided by MIT.
