Selectively Magnetizing An Anti-Ferromagnet With Terahertz Laser

January 13, 2025 by Maya Posch 9 Comments

It’s a well-known fact that anti-ferromagnetic materials are called that way because they cannot be magnetized, not even in the presence of a very strong external magnetic field. The randomized spin state is also linked with any vibrations (phonons) of the material, ensuring that there’s a very strong resistance to perturbations. Even so, it might be possible to at least briefly magnetize small areas through the use of THz-range lasers, as they disrupt the phonon-spin balance sufficiently to cause a number of atoms to ‘flip’, resulting in a localized magnetic structure.

The research by [Baatyr Ilyas] and colleagues was published in Nature, describing the way the 4.8 THz pulses managed to achieve this feat in FePS₃ anti-ferromagnetic material. The change in spin was verified afterwards using differently polarized laser pulses, confirming that the local structures remained intact for at least 2.5 milliseconds, confirming the concept of using an external pulse to induce phonon excitation. Additional details can be found in the supplemental information PDF for the (sadly paywalled with no ArXiv version) paper.

As promising as this sounds, the FePS₃ sample had to be cooled to 118K and kept in a vacuum chamber. The brief magnetization also doesn’t offer any immediate applications, but as a proof of concept it succinctly demonstrates the possibility of using anti-ferromagnetic materials for magnetic storage. Major benefit if such storage can be made more permanent is that it might be more stable and less susceptible to outside influences than traditional magnetic storage. Whether it can be brought out of the PoC stage into at least a viable prototype remains to be seen.

Engineering Lessons From The Super-Kamiokande Neutrino Observatory Failure

January 9, 2025 by Dan Maloney 48 Comments

Every engineer is going to have a bad day, but only an unlucky few will have a day so bad that it registers on a seismometer.

We’ve always had a morbid fascination with engineering mega-failures, few of which escape our attention. But we’d never heard of the Super-Kamiokande neutrino detector implosion until stumbling upon [Alexander the OK]’s video of the 2001 event. The first half of the video below describes neutrinos in some detail and the engineering problems related to detecting and studying a particle so elusive that it can pass through the entire planet without hitting anything. The Super-Kamiokande detector was built to solve that problem, courtesy of an enormous tank of ultrapure water buried 1,000 meters inside a mountain in Japan and lined with over 10,000 supersized photomultiplier tubes to detect the faint pulses of Chernkov radiation emitted on the rare occasion that a neutrino interacts with a water molecule.

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Polarizer clock with rainbow glow clockface

Bending Light, Bending Time: A DIY Polarizer Clock

January 7, 2025 by Heidi Ulrich 8 Comments

Imagine a clock where the colors aren’t from LEDs but a physics phenomenon – polarization. That’s just what [Mosivers], a physicist and electronics enthusiast, has done with the Polarizer Clock. It’s not a perfect build, but the concept is intriguing: using polarized light and stress-induced birefringence to generate colors without resorting to RGB LEDs.

The clock uses white LEDs to edge-illuminate a polycarbonate plate. This light passes through two polarizers—one fixed, one rotating—creating constantly shifting colours. Sounds fancy, but the process involves more trial and error than you’d think. [Mosivers] initially wanted to use polarizer-cut numbers but found the contrast was too weak. He experimented with materials like Tesa tape and cellophane, choosing polycarbonate for its stress birefringence.

The final design relies on a mix of materials, including book wrapping foil and 3D printed parts, to make things work. It has its quirks, but it’s certainly clever. For instance, the light dims towards the center, and the second polarizer is delicate and finicky to attach.

This gadget is a splendid blend of art and science, and you can see it in the video below the break. If you’re inspired, you might want to look up polariscope projects, or other birefringence hacks on Hackaday.

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Deteriorating section of the UCIL plant near Bhopal, India. (Credit: Luca Frediani, Wikimedia)

Cleaning Up Bhopal: The World’s Worst Industrial Disaster

January 7, 2025 by Maya Posch 44 Comments

Forty years ago, on the night of Sunday 2 December of 1984, people in the city of Bhopal and surrounding communities were settling in for what seemed like yet another regular night. The worst thing in their near future appeared to be having to go back to school and work the next day. Tragically, many of them would never wake up again, and for many thousands more their lives would forever be changed in the worst ways possible.

During that night, clouds of highly toxic methyl isocyanate (MIC) gas rolled through the streets and into houses, venting from the Bhopal pesticide plant until the leak petered out by 2 AM. Those who still could wake up did so coughing, with tearing eyes and stumbled into the streets to escape the gas cloud without a clear idea of where to go. By sunrise thousands were dead and many more were left severely ill.

Yet the worst was still to come, as the number of casualties kept rising, legal battles and the dodging of responsibility intensified, and the chemical contamination kept seeping into the ground at the crippled plant. Recently there finally seems to be progress in this clean-up with the removal of 337 tons of toxic waste for final disposal, but after four decades of misgivings and neglect, how close is Bhopal really to finally closing the chapter on this horrific disaster?

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Schematic for progress of 3D integration. a, Schematic showing conventional 3D integration by TSV through wafers. b, M3D integration of single-crystalline Si devices by transfer, c, Growth-based M3D integration of polycrystalline devices. d, Growth-based seamless M3D integration of single-crystalline devices. (Credit: Ki Seok Kim et al., 2024, Nature)

Growing Semiconductor Layers Directly With TMDs

January 6, 2025 by Maya Posch 5 Comments

Transition-metal dichalcogenides (TMDs) are a class of material that’s been receiving significant attention as a possible successor of silicon. Recently, a team of researchers has demonstrated the use of TMDs as an alternative to through-silicon-vias (TSV), which is the current way that multiple layers of silicon semiconductor circuitry are stacked, as seen with, e.g., NAND Flash ICs and processors with stacked memory dice. The novelty here is that the new circuitry is grown directly on top of the existing circuitry, removing the need for approaches like TSV to turn 2D layers into 3D stacks.

As reported in the paper in Nature by [Ki Seok Kim] and colleagues (gift article), this technique of monolithic 3D (M3D) integration required overcoming a number of technological challenges, most of all enabling the new TMD single-crystals to grow at low enough temperatures that it doesn’t destroy the previously created circuitry. The progress is detailed in the paper’s schematic (pictured above): from TSV to M3D by transfer of layers and high- and low-temperature growth of single-crystal layers.

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Turns Out Humans Are Terrible At Intuiting Knot Strength

January 6, 2025 by Donald Papp 36 Comments

We are deeply intuitively familiar with our everyday physical world, so it was perhaps a bit of a surprise when researchers discovered a blind spot in our intuitive physical reasoning: it seems humans are oddly terrible at judging knot strength.

One example is the reef knot (top) vs. the grief knot (bottom). One is considerably stronger than the other.

What does this mean, exactly? According to researchers, people were consistently unable to tell when presented with different knots in simple applications and asked which knot was stronger or weaker. This failure isn’t because people couldn’t see the knots clearly, either. Each knot’s structure and topology was made abundantly clear (participants were able to match knots to their schematics accurately) so it’s not a failure to grasp the knot’s structure, it’s just judging a knot’s relative strength that seems to float around in some kind of blind spot.

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Flashlight shining through gold leaf on glass

Shining Through: Germanium And Gold Leaf Transparency

January 5, 2025 by Heidi Ulrich 26 Comments

Germanium. It might sound like just another periodic table entry (number 32, to be exact), but in the world of infrared light, it’s anything but ordinary. A recent video by [The Action Lab] dives into the fascinating property of germanium being transparent to infrared light. This might sound like sci-fi jargon, but it’s a real phenomenon that can be easily demonstrated with nothing more than a flashlight and a germanium coin. If you want to see how that looks, watch the video on how it’s done.

The fun doesn’t stop at germanium. In experiments, thin layers of gold—yes, the real deal—allowed visible light to shine through, provided the metal was reduced to a thickness of 100 nanometers (or: gold leaf). These hacks reveal something incredible: light interacts with materials in ways we don’t normally observe.

For instance, infrared light, with its lower energy, can pass through germanium, while visible light cannot. And while solid gold might seem impenetrable, its ultra-thin form becomes translucent, demonstrating the delicate dance of electromagnetic waves and electrons.

The implications of these discoveries aren’t just academic. From infrared cameras to optics used in space exploration, understanding these interactions has unlocked breakthroughs in technology. Has this article inspired you to craft something new? Or have you explored an effect similar to this? Let us know in the comments!

We usually take our germanium in the form of a diode. Or, maybe, a transistor.

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