Magnet with near-zero external field could reshape future electronics
An international research team led by DTU has developed a new magnetic material that features a stable internal magnetic structure, almost no external magnetic field, and retains these properties above room temperature. These characteristics may be important for future generations of electronic technologies, for example, within fields where magnetic properties are used instead of electrical charge to process information—so-called spintronics. The results have been published in the journal Nature Chemistry.
The material belongs to a rare class known as compensated ferrimagnets. In such materials, the magnetic moments inside the structure point in different directions. Internally, magnetism is very strong, but the magnetic moments almost cancel each other out. As a result, the material exhibits only a very weak external magnetic field. This sets it apart from conventional magnets, which generate unwanted magnetic interference or "noise" that makes them difficult to integrate into electronic circuits.
A series of posts where I will explain bits and pieces of physics I have gathered throughout the my foray into this wonderful science. Warning, these will be long.
Highly inspired by @chemblrish and @minmin-vs-physics 's posts on their fields, check out their posts (linked on this post in various places!)
Wait what even is going on?
Okay, first of all, why are we even talking about spintronics, whatever that means? Now, we live in an age where we need devices, right? Phones, TVs, laptops, name it. All digital devices come under electronics, which is a cluster of what we call "logic devices" (verrry loosely speaking) with various functions, made with expert circuitry to create our sophisticated "smart" devices. Whew. That's a lot of words. But what does it mean? It means that the very device you're using to view this post is made up of very tiny mini devices, which are made to utilize electrical signals (current, flow of electrons) to make it store information, read information, or perform logic tasks ("AND", "OR" "NOT" and the rest. Let me know if you want me to explain those, but this is not the point of the post so I'm letting them hang in the air for now).
We store digital information in the form of 'bits' (I swear all of this is relevant, please be patient) which is a computer's language of storing and using information. If you've watched any show involving hacking, you'll see stacks after stacks of "1"s and "0"s on their high contrast screens in that radioactive green font (general older sister advice: don't use high contrast it hurts your eyes), these are bits and the basis on which logic devices work. Each combination of 1s and 0s makes a different information, which is the backbone of computing. Now, how these devices make 1s and 0s is again a whole course on electronics, so I will skip over it to just preface that they exist and that's how we make digital devices.
All these years, we have used semiconductors, which allow moderate amount of current flow from them (in contrast to conductors, which allow free flow of electrons, and insulators, which do not allow flow of electrons) to make transistors, which are currently the building blocks of circuit-making devices.
[here's a picture containing ICs (the bug-like looking thing covered in wires) which have tiny transistors inside them, and the LEDs, on which the lit ones are "1"s and unlit ones are "0"s. This was my project for one of my courses!]
In electronics, a very famous law called Moore's Law, states that for increase in tech and development, the amount of transistors in integrated circuits (IC) doubles every two years. This moves proportionally with the increase in use of semiconductors, because transistors are made using them.
Every device maker's main goal is to make a device faster, smoother, and more functional. Which means, more transistors, better semiconductors. Moreover, the smaller space occupied by the ICs, the better. But obviously there's a limit to how much we can decrease the size of the transistors. One is the technical issue of creating such a small object, which will require highly precise instruments which we are not in possession of/ not feasible in the long run. The second issue is the working. "Will a semiconductor keep it's properties when they layer is so small?" is a valid question to ask when we go further down in scale. In simple words: in the long run, improving semiconductors for transistors will be difficult. Moore's law plateaus, and the number of transistors doesn't double with two years. What now? We can't just stop developing better computing devices, not just smart devices, astronomy, medicine and other scientific areas also require reliable, stable and fast computing devices.
Which means we desperately need new materials (and techniques) for logic and memory devices.
Hold on, when's spintronics going to start?
Okay background information done. Now we move onto spins and why we use it. We know that atoms are made of protons, electrons and neutrons. Out of these, electrons "revolve" in "orbits" around the nucleus, which holds the protons and neutrons. I put "revolve" and "orbits" in quotes because essentially it's a cloud of probabilities and we have no clue what path it truly takes. Electrons reside in what are called 'orbitals', which are balloon-like spaces which have a high probability of the electrons being present in (@/chemblrish explains orbitals better here).
Now along with the "revolution", electrons also considered to have a "spin". We don't really know if it "spins" the way Bayblades do, but regardless, they have an angular momentum, which is classically something rotating objects possess (@/mimin-vs-physics goes more in depth on quantum mechanical fun stuff) Either way, we don't know why it has angular momentum, but we know it does (at least I have no idea if we've figured it out??). And in true human fashion, we see anything new and think "now how can I utilize this for my benefit?"
Years and years of research later, we figured out something interesting. The angular momentum which the electron spins contain, and the angular momentum of electrons in "orbits" can interact! This interaction is called Spin-Orbit Coupling (SOC) and it causes a bunch of other fascinating phenomena in quantum mechanics. One of which, is that it if we supply electricity into a metal plane, we can align the electrons and their spins in such a way that it causes a stream of current (remember: current is essentially a flow of electrons in one direction) with aligned spins to move into a different layer perpendicularly.
Okay but what does all of this have to do anything with Spintronics?
We're finally at the part where we can discuss what Spintronics is! We can use our now generated spin current to make electronic devices (hence, spintronics!). So, how do we make these tiny devices?
What we first take is a heavy metal (these are metallic elements/alloys with high atomic numbers, which have a lot of free electrons to use) and make a very thin film of it. (The procedure of making thin films is very interesting, and I will make the next post on it!) We can now pass a stream of current/electricity* parallel to the surface of the thin film, which will give us a stream of spin-aligned electrons bouncing to move into an upper layer.
For the upper layer, we add a thin layer of a ferromagnet. A ferromagnet is a type of material which readily aligns its spin on one direction when under a magnetic field (contrary to this are paramagnets which weakly align their spins, and diamagnets which weakly align their spins opposite to the applied field).
Now remember the electrons with their spin aligned which wanted to move into the upper layer? Yeah once they are given an upper layer to move into, they flow into the layer, bringing their aligned spins with them. This spin can now affect the ferromagnet's spin, and align it in either the direction of the applied electric field ( the one applied on the heavy metal layer. I'm marking it as * for you to check which electric field I mean) or directly opposite to the direction of the electric field. This alignment can be measured. The value doesn't matter, only the direction. Is it parallel to the electric field or anti-parallel? "Up" or "down"? "Left" or "right"? Or, in terms of electronics, "1" or "0".
And look! We now have a way to make a tiny device which can display values of "1" or "0"! We used an analog signal (electricity) to create a digital output (1s and 0s)! That is electronics! But because it uses spins, it is called Spintronics.
Because we use Spin-Orbit Coupling, these devices are extremely precise and fast. And the layers of heavy metal/ferromagnet will be in the ranges of nanometers (10^-9 m), so they are also extremely small. We can also choose materials with properties we like (high melting/boiling point, low reactivity) to create devices which can work in extreme conditions (high heat, pressure, reactive areas).
And here we have it! We've made spintronic devices!
End of post disclaimer: I am a Bachelors student and I will have mistakes. I also tend to exaggerate. So if I have made a mistake in this post, please inform me nicely in the comments or tags!
Interestingly, even Edwin Hall, the greatest scientists of all, who discovered the Hall effect, attempted to measure his effect using a beam
Interestingly, even Edwin Hall, the greatest scientists of all, who discovered the Hall effect, attempted to measure his effect using a beam of light with no success. He summarizes in the closing sentence of his notable paper from 1881: “I think that, if the action of silver had been one tenth as strong as that of iron, the effect would have been detected. No such effect was observed.” (E. Hall, 1881). By tuning in to the right frequency—and knowing where to look—researchers found a way to measure what was once thought invisible.
William A. Borders, Ahmed Z. Pervaiz, Shunsuke Fukami, Kerem Y. Camsari, Hideo Ohno & Supriyo Datta https://doi.org/10.1038/s41586-019-1557-9
These folks built a spintronics-based proof of concept for a (classical! room-temperature!) probabilistic computer that efficiently runs a modified adiabatic quantum algorithm for integer factorization! They used a network of 8 probabilistic “p-bits” to factorize numbers up to 945.
Beyond 0 and 1: Ferrotoroidic material can store four magnetic states
Today's computers store information using only two values: 0 and 1. But as electronic devices become smaller and reach their limits, scientists are searching for new ways to pack more information into the same space. One idea is to use magnetism. In some materials, atoms behave like tiny magnets that can arrange themselves in different patterns. If each pattern represents a different value, one memory element could store more than just two possibilities.
In a study recently published in Nature Communications, researchers have found a material in which these atomic magnets can form four different magnetic states. They showed that these states can be controlled using electric and magnetic fields and remain stable once created.
Your phone's next speed boost may come from a strange magnetic jump that rewrites how chips handle heat
A new technology has been proposed that could fundamentally solve the issue of smartphones overheating during high-spec gaming or extended video streaming. Researchers at KAIST have discovered the principle of processing signals using the minute vibrations of magnets (spin waves) instead of electrons. This method significantly reduces heat generation and power consumption while enabling instantaneous frequency switching within the several GHz range. This breakthrough is expected to pave the way for smart devices with less heat and longer battery life, as well as ultra-low-power, high-speed computing.
A research team led by Professor Kab-Jin Kim from the Department of Physics successfully achieved significant signal speed (frequency) changes at the nanoscale using spin waves—minute vibrations occurring within magnets. These vibrations are explained in units called "magnons." This achievement is being evaluated for presenting a signal control method that can drastically reduce power consumption even at extremely small scales, which was difficult to implement using conventional electron-based methods. The paper is published in the journal Nature Communications.
A familiar magnet gets stranger: Why cobalt's topological states could matter for spintronics
The element cobalt is considered a typical ferromagnet with no further secrets. However, an international team led by HZB researcher Dr. Jaime Sánchez-Barriga has now uncovered complex topological features in its electronic structure. Spin-resolved measurements of the band structure (spin-ARPES) at BESSY II revealed entangled energy bands that cross each other along extended paths in specific crystallographic directions, even at room temperature. As a result, cobalt can be considered as a highly tunable and unexpectedly rich topological platform, opening new perspectives for exploiting magnetic topological states in future information technologies.
The findings are published in the journal Communications Materials.
Cobalt is an elementary ferromagnet, and its properties and crystal structure have long been known. However, an international team has now discovered that cobalt hosts an unexpectedly rich topological electronic structure that remains robust at room temperature, revealing a surprising new level of quantum complexity in this material.
Scientists successfully develop half metal material that conducts single-spin electrons
Researchers at Forschungszentrum Jülich have successfully created the world's first experimentally verified two-dimensional half metal—a material that conducts electricity using electrons of just one spin type: either "spin-up" or "spin-down." Their findings, now published as an Editors' Suggestion in Physical Review Letters, mark a milestone in the quest for materials enabling energy-efficient spintronic that go beyond conventional electronics.
Half metals are key to spintronics: Unlike traditional conductors, half metals allow only one spin orientation to pass through. This makes them ideal candidates for spintronics, a next-generation information technology that leverages both the charge and the spin of electrons for data storage and processing. In conventional electronics, on the other hand, only the charge is used.
