Illustrative models of collinear ferromagnetism, antiferromagnetism, and altermagnetism in crystal-structure real space and nonrelativistic electronic-structure momentum space. (Credit: Libor Šmejkal et al., Phys. Rev. X, 2022)

Altermagnetism In Manganese Telluride And Others: The Future Of Spintronics?

August 1, 2024 by Maya Posch 5 Comments

Magnetic materials are typically divided into ferromagnetic and antiferromagnetic types, depending on their magnetic moments (electron spins), resulting in either macroscopic (net) magnetism or not. Altermagnetism is however a recently experimentally confirmed third type that as the name suggests alternates effectively between these two states, demonstrating a splitting of the spin energy levels (spin-split band structure). Like antiferromagnets, altermagnets possess a net zero magnetic state due to alternating electron spin, but they differ in that the electronic band structure are not Kramers degenerate, which is the feature that can be tested to confirm altermagnetism. This is the crux of the February 2024 research paper in Nature by [J. Krempaský] and colleagues.

Specifically they were looking for the antiferromagnetic-like vanishing magnetization and ferromagnetic-like strong lifted Kramers spin degeneracy (LKSD) in manganese telluride (MnTe) samples, using photoemission spectroscopy in the UV and soft X-ray spectra. A similar confirmation in RuO2 samples was published in Science Advances by [Olena Fedchenko] and colleagues.

What this discovery and confirmation of altermagnetism means has been covered previously in a range of papers ever since altermagnetism was first proposed in 2019 by [Tomas Jungwirth] et al.. A 2022 paper published in Physical Review X by [Libor Šmejkal] and colleagues details a range of potential applications (section IV), which includes spintronics. Specific applications here include things like memory storage (e.g. GMR), where both ferromagnetic and antiferromagnetics have limitations that altermagnetism could overcome.

Naturally, as a fairly new discovery there is a lot of fundamental research and development left to be done, but there is a good chance that within the near future we will see altermagnetism begin to make a difference in daily life, simply due to how much of a fundamental shift this entails within our fundamental understanding of magnetics.

Heading image: Illustrative models of collinear ferromagnetism, antiferromagnetism, and altermagnetism in crystal-structure real space and nonrelativistic electronic-structure momentum space. (Credit: Libor Šmejkal et al., Phys. Rev. X, 2022)

A finger points at a diagram of a battery with two green bars. Above it is another battery with four smaller green bars with a similar area to the first battery's two. The bottom batter is next to a blue box with a blue wave emanating from it and the top battery has a red box with a red wave emanating from it. Below the red wave is written "2x wavelength" and below the top battery is "1/2 energy in a photon."

What Are Photons, Anyway?

August 1, 2024 by Navarre Bartz 33 Comments

Photons are particles of light, or waves, or something like that, right? [Mithuna Yoganathan] explains this conundrum in more detail than you probably got in your high school physics class.

While quantum physics has been around for over a century, it can still be a bit tricky to wrap one’s head around since some of the behaviors of energy and matter at such a small scale aren’t what we’d expect based on our day-to-day experiences. In classical optics, for instance, a brighter light has more energy, and a greater amplitude of its electromagnetic wave. But, when it comes to ejecting an electron from a material via the photoelectric effect, if your wavelength of light is above a certain threshold (bigger wavelengths are less energetic), then nothing happens no matter how bright the light is.

Scientists pondered this for some time until the early 20th Century when Max Planck and Albert Einstein theorized that electromagnetic waves could only release energy in packets of energy, or photons. These quanta can be approximated as particles, but as [Yoganathan] explains, that’s not exactly what’s happening. Despite taking a few classes in quantum mechanics, I still learned something from this video myself. I definitely appreciate her including a failed experiment as anyone who has worked in a lab knows happens all the time. Science is never as tidy as it’s portrayed on TV.

If you want to do some quantum mechanics experiments at home (hopefully with more luck than [Yoganathan]), then how about trying to measure Planck’s Constant with a multimeter or LEGO? If you’re wondering how you might better explain electromagnetism to others, maybe this museum exhibit will be inspiring.

Continue reading “What Are Photons, Anyway?” →

Secret Messages On Plastic, Just Add Tesla Coil

August 1, 2024 by Donald Papp 15 Comments

Here’s a short research paper from 2013 that explains how to create “hydroglyphics”, or writing with selecting surface wetting. In it, an apparently normal-looking petri dish is treated so as to reveal a message when wetted with water vapor. The contrast between hydrophobic and hydrophilic surfaces, which is not visible to the naked eye, becomes visible when misted with water. All it took was a mask, and a little treatment with a modified Tesla coil.

Plastics tend to be hydrophobic, meaning their surface repels water. These plastics also tend to be non-receptive to things like inks and adhesives. However, there is an industrial process called corona treatment (invented by Verner Eisby in 1951) that changes the surface energy of materials like plastics, rendering them more receptive to inks, coatings, and adhesives. Eisby’s company Vetaphone still exists today, and has a page describing the process.

What’s this got to do with the petri dishes and their secret messages? The process is essentially the same. By using a Tesla coil modified with a metal wire mesh, the surface of the petri dish is exposed to the coil’s discharge, altering its surface energy and rendering it hydrophilic. By selectively blocking the discharge with a nonconductive mask made from a foam sticker, the masked area remains hydrophobic. Mist the surface with water, and the design becomes visible.

The effects of corona treatment decay over time, but we think this is exactly the sort of thing that is worth keeping in mind just in case it ever comes in useful. Compact Tesla coils are fairly easy to get a hold of nowadays, but it’s also possible to make your own.

Climate Change May Make Days Longer

July 31, 2024 by Navarre Bartz 31 Comments

For those who say there’s never enough time in a day, your wish for more time is getting granted, if ever so slightly. Scientists have now found a new source of our days getting longer — climate change.

You may have already been aware that the length of the day on Earth has been getting longer over time due to the drag exerted on our planet by our friendly neighborhood Moon. Many other factors come into play though, including the Earth’s own mass distribution. As the Earth warms and polar caps melt, the water redistributes to the Earth’s equator causing it to slow more rapidly.

In the worst-case scenario, RCP8.5, it would result in climate-related effects to planetary rotational velocity even larger than those caused by lunar tides. Under that scenario, the earth would probably be a less pleasant place to live in many other ways, but at least you’d have a little more time in your day.

While we’re talking about time, we wonder what ever happened to getting rid of Daylight Savings in the US? If you long for a simpler time, perhaps you should take up repairing mechanical watches and clocks?

A bright orange sailboat with solar panels on the wing sail and the hull of the craft. A number of protuberances from the wing are visible containing instruments and radio equipment.

Saildrones Searching The Sea For Clues To Hurricane Behavior

July 29, 2024 by Navarre Bartz 26 Comments

Hurricanes can cause widespread destruction, so early forecasting of their strength is important to protect people and their homes. The US National Oceanic and Atmospheric Administration (NOAA) is using saildrones to get better data from inside these monster storms.

Rising ocean temperatures due to climate change are causing hurricanes to intensify more rapidly than in the past, although modeling these changes is still a difficult task. People on shore need to know if they’re in store for a tropical storm or a high strength hurricane to know what precautions to take. Evacuating an area is expensive and disruptive, so it’s understandable that people want to know if it’s necessary.

Starting with five units in 2021, the fleet has gradually increased in size to twelve last summer. These 23ft (7m), 33ft (10m), or 65ft (20m) long vessels are propelled by wing sails and power their radio and telemetry systems with a combination of solar and battery power. No fossil fueled vessel can match the up to 370 days at sea without refueling that these drones can achieve, and the ability to withstand hurricane winds and sea conditions allow scientists an up-close-and-personal look at a hurricane without risking human lives.

We’ve covered how the data gets from a saildrone to shore before, and if you want to know how robots learn to sail, there’s a Supercon talk for that.

Thanks to [CrLz] for the tip!

On the left, a transluscent yellowy-tan android head with eyes set behind holes in the face. On the right, a bright pink circle with small green eyes. It is manipulated into the image of a smiling face via its topography.

A Robot Face With Human Skin

July 25, 2024 by Navarre Bartz 30 Comments

Many scifi robots have taken the form of their creators. In the increasingly blurry space between the biological and the mechanical, researchers have found a way to affix human skin to robot faces. [via NewScientist]

Previous attempts at affixing skin equivalent, “a living skin model composed of cells and extracellular matrix,” to robots worked, even on moving parts like fingers, but typically relied on protrusions that impinged on range of motion and aesthetic concerns, which are pretty high on the list for robots designed to predominantly interact with humans. Inspired by skin ligaments, the researchers have developed “perforation-type anchors” that use v-shaped holes in the underlying 3D printed surface to keep the skin equivalent taut and pliable like the real thing.

The researchers then designed a face that took advantage of the attachment method to allow their robot to have a convincing smile. Combined with other research, robots might soon have skin with touch, sweat, and self-repair capabilities like Data’s partial transformation in Star Trek: First Contact.

We wonder what this extremely realistic humanoid hand might look like with this skin on the outside. Of course that raises the question of if we even need humanoid robots? If you want something less uncanny, maybe try animating your stuffed animals with this robotic skin instead?

Manually Computing Logarithms To Grok Calculators

July 24, 2024 by Maya Posch 20 Comments

Logarithms are everywhere in mathematics and derived fields, but we rarely think about how trigonometric functions, exponentials, square roots and others are calculated after we punch the numbers into a calculator of some description and hit ‘calculate’. How do we even know that the answer which it returns is remotely correct? This was the basic question that [Zachary Chartrand] set out to answer for [3Blue1Brown]’s Summer of Math Exposition 3 (SoME-3). Inspired by learning to script Python, he dug into how such calculations are implemented by the scripting language, which naturally led to the standard C library. Here he found an interesting implementation for the natural algorithm and the way geometric series convergence is sped up.

The short answer is that fundamental properties of these series are used to decrease the number of terms and thus calculations required to get a result. One example provided in the article reduces the naïve approach from 36 terms down to 12 with some optimization, while the versions used in the standard C library are even more optimized. This not only reduces the time needed, but also the memory required, both of which makes many types of calculations more feasible on less powerful systems.

Even if most of us are probably more than happy to just keep mashing that ‘calculate’ button and (rightfully) assume that the answer is correct, such a glimpse at the internals of the calculations involved definitely provides a measure of confidence and understanding, if not the utmost appreciation for those who did the hard work to make all of this possible.