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.

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Getting An Old HVAC System Online

August 1, 2024 by Bryan Cockfield 14 Comments

Standardization might sound boring, but it’s really a great underlying strength of modern society. Everyone agreeing on a way that a certain task should be done saves a lot of time, energy, and money. But it does take a certain amount of consensus-building, and at the time [JC]’s HVAC system was built the manufacturers still hadn’t agreed on a standard control scheme for these machines yet. But with a little ingenuity and an Arduino, the old HVAC system can be given a bit of automatic control.

The original plan for this antiquated system, once off-the-shelf solutions were found to be incompatible, was to build an interface for the remote control. But this was going to be overly invasive and complex. Although the unit doesn’t have a standard remote control system, it does have extensive documentation so [JC] was able to build a relay module for it fairly easily with an Arduino Nano Matter to control everything and provide WiFi functionality. It also reports the current status of the unit and interfaces with the home automation system.

While some sleuthing was still needed to trace down some of the circuitry of the board to make sure everything was wired up properly, this was a much more effective and straightforward (not to mention inexpensive) way of bringing his aging HVAC system into the modern connected world even through its non-standardized protocols. And, although agreeing on standards can sometimes be difficult, they can also be powerful tools once we all agree on them.

A painted RC plane made of cardboard. It has an orange propeller and camo-esque markings along with concentric blue, white, and red circles near the wingtips.

Cardboard R/C Plane Actually Flies

August 1, 2024 by Navarre Bartz 19 Comments

Many makers start by building mock-ups from cardboard, but [Alex-08] has managed to build an R/C plane that actually flies, out of cardboard.

If you’ve been thinking of building an R/C plane from scratch yourself, this guide is an excellent place to start. [Alex-08] goes through excruciating detail on how he designed and constructed this marvel. The section on building the wings is particularly detailed since that’s the most crucial element in making sure this plane can get airborne.

Some off-the-shelf R/C parts and 3D printed components round out the parts list to complement the large cardboard box used for most of the structural components. The build instructions even go through some tips on getting that vintage aircraft feel and how to adjust everything for a smooth flight.

Need a wind tunnel instead? You can build that out of cardboard too. If paper airplanes are more your thing, how about launching them from space? And if you’re just trying to get a head start on Halloween, why not laser cut an airplane costume from cardboard?

2024 Tiny Games Contest: Pi-O-Scope-Pong

August 1, 2024 by Donald Papp 3 Comments

[Aaron Lager]’s Pi-O-Scope-Pong project takes a minimal approach to Pong by drawing on an oscilloscope to generate crisp paddles and ball. A Raspberry Pi takes care of the grunt work of signal generation, and even uses the two joysticks of an Xbox controller (connected to the Pi over Bluetooth) for inputs.

Originally, [Aaron] attempted to generate the necessary signals directly from the Pi’s PWM outputs by doing a little bit of RC filtering on the outputs, but was repulsed by the smeary results. The solution? An old but perfectly serviceable 8-bit MAX506 DAC now handles crisping up the visuals with high-quality analog outputs. Code is available on the project’s GitHub repository.

There isn’t any score-keeping or sound, but one thing that it has over the original Pong is a round ball. The ball in the original Pong game was square, but mainly because cost was a concern during design and generating a round ball would have ballooned the part count.

In many ways, Pong itself is a great inspiration for the Tiny Games Challenge, because the simplicity of its gameplay was likely a big part of its success.

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The Atomic Gardener Of Eastbourne

August 1, 2024 by Jenny List 6 Comments

Pity the video team at a large hacker camp, because they have a huge pile of interesting talks in the can but only the limited resources of volunteers to put them online. Thus we often see talks appearing from past camps, and such it is with one from Electromagnetic Field 2022. It’s from [Sarah Angliss], and as its subject it takes the extraordinary work of [Muriel Howorth], a mid-20th-century British proponent of irradiated seeds as a means to solve world hunger.

Today we are used to genetic modification in the context of plants, and while it remains a controversial subject, the science behind it is well known. In the period following the Second World War there was a different approach to improving crops by modifying their genetics: irradiating seeds in a scattergun approach to genetic modification, in the hope that among thousands of duds there might be a mutant with special properties.

To this came Muriel Howorth, at first charged with telling the story of atomic research for the general public. She took irradiated seeds from Oak Ridge in the USA, and turned them into a citizen science program, with an atomic gardening society who would test these seeds and hopefully, find the supercrops within. It’s a wonderfully eccentric tale that might otherwise be the plot of a Wallace and Gromit movie, and but for a few interested historians of popular science it might otherwise have slipped into obscurity. We’re sorry we didn’t catch this one live back when we attended the event.

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Programming Ada: Implementing The Lock-Free Ring Buffer

August 1, 2024 by Maya Posch 20 Comments

In the previous article we looked at designing a lock-free ring buffer (LFRB) in Ada, contrasting and comparing it with the C++-based version which it is based on, and highlighting the Ada way of doing things. In this article we’ll cover implementing the LFRB, including the data request task that the LFRB will be using to fill the buffer with. Accompanying the LFRB is a test driver, which will allow us to not only demonstrate the usage of the LFRB, but also to verify the correctness of the code.

This test driver is uncomplicated: in the main task it sets up the LFRB with a 20 byte buffer, after which it begins to read 8 byte sections. This will trigger the LFRB to begin requesting data from the data request task, with this data request task setting an end-of-file (EoF) state after writing 100 bytes. The main task will keep reading 8-byte chunks until the LFRB is empty. It will also compare the read byte values with the expected value, being the value range of 0 to 99.

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