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.

Creating And Control Of Magnetic Skyrmions In Ferromagnetic Film Demonstrated

November 21, 2024 by Maya Posch 22 Comments

Visualization of magnetic skyrmions. (Credit: KRISS)

Magnetic skyrmions are stable quasi-particles that can be generated in (some) ferromagnetic materials with conceivable solutions in electronics, assuming they can be created and moved at will. The creation and moving of such skyrmions has now been demonstrated by [Yubin Ji] et al. with a research article in Advanced Materials. This first ever achievement by these researchers of the Korea Research Institute of Standards and Science (KRISS) was more power efficient than previously demonstrated manipulation of magnetic skyrmions in thicker (3D) materials.

Magnetic skyrmions are sometimes described as ‘magnetic vortices’, forming statically stable solitons. For magnetic skyrmions their stability comes from the topological stability, as changing the atomic spin of the atoms inside the skyrmion would require overcoming a significant energy barrier.

In the case of the KRISS researchers, electrical pulses together with a magnetic field were used to create magnetic skyrmions in the ferromagnetic (Fe₃GaTe₂, or FGaT) film, after which a brief (50 µs) electric current pulse was applied. This demonstrated that the magnetic skyrmions can be moved this way, with the solitons moving parallel to the electron flow injection, making them quite steerable.

While practical applications of magnetic skyrmions are likely to be many years off, it is this kind of fundamental research that will enable future magnetic storage and spintronics-related devices.

Featured image: Direct imaging of the magnetic skyrmions. The scale bars represent 300 nm. (Credit:Yubin Ji et al., Adv. Mat. 2024)

Crystal structure of Cr2Te3 thin films. (Credit: Hang Chi et al. 2023)

Chromium(III) Telluride As Ferromagnetic Material With Tunable Anomalous Hall Effect

November 29, 2023 by Maya Posch 7 Comments

Chromium(III) Telluride (Cr₂Te₃) is an interesting material for (ferro)magnetic applications, with Yao Wen and colleagues reporting in a 2020 Nano Letters paper that they confirmed it to show spontaneous magnetization at a thickness of less than fifty nanometers, at room temperature. Such a 2D ferromagnet could be very useful for spintronics and other applications. The confirmation of magnetization is performed using a variety of methods, including measuring the Hall Effect (HE) and the Anomalous Hall Effect (AHE), the latter of which is directly dependent on the magnetization of the material, rather than an externally applied field.

More recently, in a June 2023 article by Hang Chi and colleagues in Nature Communications, it is described how such epitaxially obtained Cr₂Te₃ films show a distinct change in the AHE (in the form of sign reversal) depending on the strain induced by the interface with the various types of substrates (Al₂O₃, SrTiO₃) and the temperature, likely owing to the different thermal expansion rates of the film and substrate. Underlying this change in the observed AHE is the Berry phase and the related curvature. This is a phenomenon that was also noted by Quentin Guillet and colleagues in their 2023 article in Physical Review Materials, effectively independently confirming the AHE

Using Cr₂Te₃ in combination with the appropriate substrate might ultimately lead to spintronics-based memory and other devices, even if such applications will still take considerable R&D.

Top image: Crystal structure of Cr₂Te₃ thin films. (Credit: Hang Chi et al. 2023)

solenoid wound pickup coil next to a selection of bolts and a steel rod

The Barkhausen Effect: Hearing Magnets Being Born

November 19, 2022 by Dave Rowntree 21 Comments

The Barkhausen effect — named after German Physicist Heinrich Barkhausen — is the term given to the noise output produced by a ferromagnetic material due to the change in size and orientation of its discrete magnetic domains under the influence of an external magnetic field. The domains are small: smaller than the microcrystalline grains that form the magnetic material, but larger than the atomic scale. Barkausen discovered that as a magnetic field was brought close to a ferrous material, the local magnetic field would flip around randomly, as the magnetic domains rearranged themselves into a minimum energy configuration and that this magnetic field noise could be sensed with an appropriately arranged pickup coil and an amplifier. In the short demonstration video below, this Barkhausen noise can be fed into an audio amplifier, producing a very illustrative example of the effect.

One example of practical use for this effect is with non-destructive testing and qualification of magnetic structures which may be subject to damage in use, such as in the nuclear industry. Crystalline discontinuities or impurities within a part under examination result in increased localized mechanical stresses, which could result in unexpected failure. The Barkhausen noise effect can be easily leveraged to detect such discontinuities and give the evaluator a sense of the condition of the part in question. All in all, a useful technique to know about!

If you were thinking that the Barkhausen is a familiar name, you may well be thinking about the Barkhausen stability criterion, which is fundamental to describing some of the conditions necessary for a linear feedback circuit to oscillate. We’ve covered such circuits before, such as this dive into bridge oscillators.

Continue reading “The Barkhausen Effect: Hearing Magnets Being Born” →

Digital Hourglass Counts Down The Seconds

October 26, 2022 by Adam Fabio 20 Comments

If someone asked you to build a digital hourglass, what would your design look like? [BitBlt_Korry] took on that challenge, creating a functional art piece that hits it right on the nose: an hourglass with a digital display.

Iron filings fall between two pieces of plexiglass while ghostly numbers appear, counting down 30 seconds. Just as quickly as they appear, the numbers disappear – dropping down to the bottom of the enclosure. Each second is punctuated by what might be the loudest clock tick we’ve ever heard.

Of course, it’s not all magic. The hourglass is controlled by a Raspberry Pi Pico running code in MicroPython. The pico drives a series of transistors, which in turn are used to control 14 solenoids. The solenoids serve double duty — first, they move pieces of flat “fridge magnet” material close enough to attract iron filings. Their second duty is of course provide a clock tick that will definitely get your attention.

Tilt sensors are the user input to the hourglass, letting the Pi Pico know which end is up when it’s time to start a new 30-second countdown.

[BitBlt_Korry] mentions that the hardest part of the project was setting the screws at the top and bottom of the hourglass to get the perfect uniform flow of iron filings.

[BitBlt_Korry] calls his creation “「時場(じば)」”. Google translates this to “Jiba”, which means “magnetic field”. We’re not native speakers, but we’re guessing there is a double meaning there.

This isn’t the first time we’ve seen humble iron filings stand up and dance at our command. If iron dust is too dry a topic, we’ve got plenty of ferrofluid projects as well!

Continue reading “Digital Hourglass Counts Down The Seconds” →

Your Next Wearable May Not Need Electricity

November 17, 2017 by Kristina Panos 9 Comments

What if you could unlock a door with your shirtsleeve, or code a secret message into your tie? This could soon be a thing, because researchers at the University of Washington have created a fabric that can store data without any electronics whatsoever. The fabric can be washed, dried, and even ironed without losing data. Oh, and it’s way cheaper than RFID.

By harnessing the ferromagnetic properties of conductive thread, [Justin Chen] and [Shyam Gollakota] have proved the ability to store bit strings and 2D images through magnetization. The team used an embroidery machine to lay down thread in dense strips and patches, and then coded in ones and zeros by rubbing the threads with N and S neodymium magnets.

They didn’t use anything special, either, just this conductive thread, some magnets, and a Nexus 5 to read the data. Any phone with a magnetometer (so, most of them) could decode this type of binary data. The threads stay reliably magnetized for about a week and then begin to weaken. However, their tests proved that the threads can be re-magnetized over and over.

The team also created 2D images with magnets on a 9-patch made of conductive fabric. The images can be decoded piecemeal by a single magnetometer, or all at once by an array of them. Finally, the team made a glove with a magnetized patch of thread on the fingertip. They were able to get the phone to recognize six unique gestures with 90% accuracy, even with the phone tucked away in a pocket. See it in action in their demo video after the break.

Magnetic memory is certainly not a new concept. But for the wearable technology frontier, it’s a novel one.

Continue reading “Your Next Wearable May Not Need Electricity” →

New Magnetic Semiconductor

November 23, 2015 by Al Williams 27 Comments

When you think of South Dakota you generally think of Mount Rushmore and, maybe, nuclear missiles. However, [Simeon Gilbert] will make you think of semiconductors. [Simeon], a student at South Dakota State University, won first place at the annual Sigma Xi national conference because of his work on a novel magnetic semiconductor.

The material, developed in collaboration with researchers from the nano-magnetic group at the University of Nebraska-Lincoln, is a mix of cobalt, iron, chromium, and aluminum. However, some of the aluminum is replaced with silicon. Before the replacement, the material maintained its magnetic properties at temperatures up to 450F. With the silicon standing in for some of the aluminum atoms, the working temperature is nearly 1,000F.

Continue reading “New Magnetic Semiconductor” →