光励起による電子制御 – 磁鉄鉱は次世代デバイスの幕開けになるか？

スピントロニクスの可能性

Electronic components like transistors are traditionally built out of silicon and rely on semiconductors. The 0 and 1 signals in binary indicate the passing or blocking of an electric current. An alternative way to perform computation is spintronics devices that run on the spin of electrons (a fundamental quantum characteristic) rather than electric current (flow of electrons).
スピントロニクスは従来の電子システムに比べていくつかの利点があります, notably:

• スピンははるかに速く変化できるため、データ転送が高速です。
• 電流を維持するために必要な電子フラックスよりも少ない電力でスピンを変化させられるため、エネルギー消費が少なくなります。
• 複雑な半導体材料の代わりに、単純な金属を使用できます。

Spintronics is notably used for hard drives and has allowed storage capacity to grow over the last decade.

A material already used in spintronics is 磁鉄鉱, a naturally occurring mineral made of oxygen and two forms of iron at different levels of oxidation.

出典: Britannica

磁鉄鉱は何十年も磁気特性で知られてきましたが、まだ学べることがあるようです。

Researchers from the EPFL in Switzerland have discovered that lasers can create new phase changes in magnetite that were previously unknown. This could, in turn, lead to a new generation of electronic equipment.

磁鉄鉱の隠れた特性

The researchers focused on magnetite due to its metal-to-insulator properties, allowing it to switch from a conductor of electricity to blocking it. This is also known as a phase transition, where the properties of a material suddenly change from one stage to another, a little like how liquid water can turn into ice, with very different properties.

By using two different types of lasers, one emitting light at 800nm and one at 400nm (infrared and visible light), they discovered that new phases appeared in magnetite that had not been identified until now.

This is not a trivial matter, as the researchers had to detect change happening in an infinitesimally small period of time. To do so, they used a technique called 超高速電子回折 (UED), which allowed them to look at atom movements lasting less than a picosecond or a trillionth of a second.

空間構成の変化

Normally, magnetite’s atomic structure is “a monoclinic lattice,” where the unit cell is shaped like a skewed box with three unequal edges. Two of its angles are 90 degrees, while the third is different.

出典: ACS

The 800nm light causes the magnetite atomic structure to compress, turning it into a cubic structure. The ultra-rapid observation showed the researchers that it happened through a 3-stage process.

The 400nm instead caused the metal atomic structure to expand, creating a very stable configuration, making it a very stable insulator.

This configuration is different from the previously known stable equilibrium of magnetite and provides deep insight into what is actually happening during the metal-to-insulator transition.

新しい電子システム

This discovery means that it is possible to change the effect on spin and current of magnetite just with light from lasers.

Thanks to very quick laser systems, it could allow for photon pulse to quickly change in a controlled fashion the nature of the metallic material.

“Our study breaks ground for a novel approach to control matter at ultrafast timescale using tailored photon pulses.

Being able to induce and control hidden phases in magnetite could have significant implications for the development of advanced materials and devices.

For instance, materials that can switch between different electronic states quickly and efficiently could be used in next-generation computing and memory devices.”

より優れたメモリ

Spintronics and magnetite are new frontiers for electronic system manufacturers. What started in a hard drive is now expanding to other memory systems.

For example, random access memory (DRAM) could be replaced with magnetic RAM (MRAM). The first version of this concept is an already commercialized product by Everspin and has been used in Airbus aircraft, thanks to its resistance to temperature changes as well as cosmic radiation compared to traditional memory systems.

Another advantage of MRAM is its smaller size and lower power consumption, which means up to 80% less power demand. This can allow MRAM to be incorporated as cache memory in processors at a greater total capacity while consuming less power and generating less heat, with both space and heat becoming key limiting factors in processor improvement.

フォトニクス？

The use of laser in changing magnetite conditions is reminiscent of the growing field of photonics, one of the options we discussed 半導体システムを超えて計算を行う企業に関する記事.

A system already using laser and light to perform computation could greatly benefit from a memory system that relies on magnetite’s phase change induced by light. This could potentially allow the computation result to be directly converted into data with little intermediary step‑consuming power and slowing things up.

スピントロニクス企業

1. Everspin Technologies

EverspinはFreescale（現在はNXP、株式コードNXPI）の部門で、MRAMメモリシステムの開発に特化しています。2016年にスピンアウトされ、IPOを実施しました。

EverspinはMRAM技術のリーダーと見なされており、Freescaleが2006年に世界初のMRAMチップを商用化した経験を継承しています。

Because MRAM is a memory that persists even in the absence of a current, it is increasingly used in sensitive use cases where critical data are important.

データ分析、クラウドコンピューティング、地上・宇宙を問わないアプリケーション、人工知能（AI）や産業用IoTを含むエッジAIなど、広範な用途に駆動され、永続メモリ市場は2020年から2030年までに年平均成長率27.5％で拡大すると予測されています。Everspin

出典: Everspin

The company estimates the market will reach a $7.4B size by 2027. The company has no debt and positive free cash flow since 2021.

Everspin MRAM products are currently occupying a small but growing niche, serving markets where reliability is crucial like aerospace, satellites, data recorders, patient monitoring devices, etc.

出典: Everspin

The growth of chipsets, AI, and synaptic systems might also be a long-term boost for the company.

2. NVE Corporation

Another leader of spintronics, NVEは、1995年にMRAM技術に関する最初の特許を取得して以来、この技術に取り組んできました。

It produces spintronic センサー and アイソレータ, mostly used in measurement and sensor systems for cars, gears, medical devices, power supplies, and other industrial devices.

出典: NVE

This puts NVE in a somewhat different category than Everspin, with NVE more of an industrial company with a strong position in a niche market (magnetometer using spintronics), while Everspin is more of a memory/computing company working with and in competition with the like of Intel, Qualcomm, Toshiba, and Samsung also developing their own MRAM product.

It can make it a more (or less) attractive stock depending on investors’ profile, with NVE’s stock more likely to appeal to more conservative investors looking for some dividend yield and safety.