Transistors, the building blocks of modern electronics, are typically made of silicon. Because it’s a semiconductor, this material can control the flow of electricity in a circuit. But silicon has fundamental physical limits that restrict how compact and energy-efficient a transistor can be.

MIT researchers have now replaced silicon with a magnetic semiconductor, creating a magnetic transistor that could enable smaller, faster, and more energy-efficient circuits. The material’s magnetism strongly influences its electronic behavior, leading to more efficient control of the flow of electricity. 

The team used a novel magnetic material and an optimization process that reduces the material’s defects, which boosts the transistor’s performance.

The material’s unique magnetic properties also allow for transistors with built-in memory, which would simplify circuit design and unlock new applications for high-performance electronics.

“People have known about magnets for thousands of years, but there are very limited ways to incorporate magnetism into electronics. We have shown a new way to efficiently utilize magnetism that opens up a lot of possibilities for future applications and research,” says Chung-Tao Chou, an MIT graduate student in the departments of Electrical Engineering and Computer Science (EECS) and Physics, and co-lead author of a paper on this advance.

Chou is joined on the paper by co-lead author Eugene Park, a graduate student in the Department of Materials Science and Engineering (DMSE); Julian Klein, a DMSE research scientist; Josep Ingla-Aynes, a postdoc in the MIT Plasma Science and Fusion Center; Jagadeesh S. Moodera, a senior research scientist in the Department of Physics; and senior authors Frances Ross, TDK Professor in DMSE; and Luqiao Liu, an associate professor in EECS, and a member of the Research Laboratory of Electronics; as well as others at the University of Chemistry and Technology in Prague. The paper appears today in Physical Review Letters.

Overcoming the limits

In an electronic device, silicon semiconductor transistors act like tiny light switches that turn a circuit on and off, or amplify weak signals in a communication system. They do this using a small input voltage.

But a fundamental physical limit of silicon semiconductors prevents a transistor from operating below a certain voltage, which hinders its energy efficiency.

To make more efficient electronics, researchers have spent decades working toward magnetic transistors that utilize electron spin to control the flow of electricity. Electron spin is a fundamental property that enables electrons to behave like tiny magnets.

So far, scientists have mostly been limited to using certain magnetic materials. These lack the favorable electronic properties of semiconductors, constraining device performance.

“In this work, we combine magnetism and semiconductor physics to realize useful spintronic devices,” Liu says.

The researchers replace the silicon in the surface layer of a transistor with chromium sulfur bromide, a two-dimensional material that acts as a magnetic semiconductor.

Due to the material’s structure, researchers can switch between two magnetic states very cleanly. This makes it ideal for use in a transistor that smoothly switches between “on” and “off.”

“One of the biggest challenges we faced was finding the right material. We tried many other materials that didn’t work,” Chou says.

They discovered that changing these magnetic states modifies the material’s electronic properties, enabling low-energy operation. And unlike many other 2D materials, chromium sulfur bromide remains stable in air.

To make a transistor, the researchers pattern electrodes onto a silicon substrate, then carefully align and transfer the 2D material on top. They use tape to pick up a tiny piece of material, only a few tens of nanometers thick, and place it onto the substrate.

“A lot of researchers will use solvents or glue to do the transfer, but transistors require a very clean surface. We eliminate all those risks by simplifying this step,” Chou says.

Leveraging magnetism

This lack of contamination enables their device to outperform existing magnetic transistors. Most others can only create a weak magnetic effect, changing the flow of current by a few percent or less. Their new transistor can switch or amplify the electric current by a factor of 10.

They use an external magnetic field to change the magnetic state of the material, switching the transistor using significantly less energy than would usually be required.

The material also allows them to control the magnetic states with electric current. This is important because engineers cannot apply magnetic fields to individual transistors in an electronic device. They need to control each one electrically.

The material’s magnetic properties could also enable transistors with built-in memory, simplifying the design of logic or memory circuits.

A typical memory device has a magnetic cell to store information and a transistor to read it out. Their method can combine both into one magnetic transistor.

“Now, not only are transistors turning on and off, they are also remembering information. And because we can switch the transistor with greater magnitude, the signal is much stronger so we can read out the information faster, and in a much more reliable way,” Liu says.

Building on this demonstration, the researchers plan to further study the use of electrical current to control the device. They are also working to make their method scalable so they can fabricate arrays of transistors.

This research was supported, in part, by the Semiconductor Research Corporation, the U.S. Defense Advanced Research Projects Agency (DARPA), the U.S. National Science Foundation (NSF), the U.S. Department of Energy, the U.S. Army Research Office, and the Czech Ministry of Education, Youth, and Sports. The work was partially carried out at the MIT.nano facilities.

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Following criticism, lawmakers have narrowed the GUARD Act, a bill aimed at restricting minors’ access to certain AI systems. The earlier version could have applied broadly to nearly every AI-powered chatbot or search tool. The amended bill focuses more narrowly on so-called “AI companions”—conversational systems designed to simulate emotional or interpersonal interactions with users. 

That change does address some of the broadest concerns raised about the original proposal, though some questions about the bill’s reach remain. Bottom line: the revised bill still creates serious problems for privacy, online speech, and parental choice.

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Tell Congress: oppose the guard act

The new GUARD Act still requires companies offering AI companions to implement burdensome age-verification systems tied to users’ real-world identities. Even parents who specifically want their teenagers to use these systems would still face significant hurdles. A family might decide that a conversational AI tool helps an isolated teenager practice social interaction, or engage in harmless creative roleplay. A parent deployed in the military might set up a persistent AI storyteller for a younger child. Under the revised bill, those users could still face mandatory age checks tied to sensitive personal or financial information before they or their children can use these services.

The revised bill also leaves important definitions unclear while sharply increasing penalties for developers and companies that get those judgments wrong. Congress narrowed the GUARD Act. But it is still trying to solve a complicated social problem with vague legal standards, heavy liability, and privacy-invasive verification systems.

Intrusive Age-Verification Remains In The Bill

The revised GUARD Act still requires companies offering AI companions to verify that users are adults through a “reasonable age verification” system. The bill allows a broader set of verification methods than the earlier version, but they are still tied to a user’s real-world identity—such as financial records, or age-verified accounts for a mobile operating system or app store. 

That approach still raises serious privacy and access concerns. Millions of Americans do not have current government ID, accounts at major banks, or stable access to the kinds of digital identity systems the bill contemplates. Even for those who do, requiring identity-linked verification to access online speech tools creates real risks for privacy, anonymity, and data security. Many people are rightly creeped out by age-verification systems, and may simply forgo using these services rather than compromise their privacy and security.

The revised definition of “AI companion” is also narrower than before, but it’s unclear at the margins. The bill now focuses on systems that “engage in interactions involving emotional disclosures” from the user, or present a “persistent identity, persona or character.” 

EFF appreciates that the authors recognized that the prior definition could reach a variety of AI systems that are not chatbots, including internet search engines. But the narrowed definition could be read to also apply to a variety of chat tools that are not AI companions. For example, many modern online conversational systems increasingly recognize and respond to users’ emotions. Customer service systems, including completely human-powered ones that existed long before AI chatbots, have long been designed to recognize frustration and respond empathetically. As conversational AI becomes more emotionally responsive, a customer service chatbot’s efforts to empathize may sweep it within the bill’s definition. 

Bigger Penalties, Bigger Incentives To Restrict Access

The revised bill also sharply increases penalties. Instead of $100,000 per violation, companies—including small developers—can face fines of up to $250,000 per violation, enforced by both federal and state officials.

That kind of liability creates incentives to over-restrict access, especially for minors. Smaller developers, in particular, may decide it is safer to block younger users entirely, disable conversational features, or avoid developing certain tools at all, rather than risk severe penalties under vague standards.

The concerns driving this bill are real. Some AI systems have engaged in troubling interactions with vulnerable users, including minors. But the right answer to that is targeted enforcement against bad actors, and privacy laws that protect us all. The revised GUARD Act instead responds with a privacy-invasive system that burdens the right to speak, read, and interact online.

Congress did improve this bill, but EFF’s core speech, privacy, and security issues remain.

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Tell Congress: oppose the guard act

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As usual, you can also use this squid post to talk about the security stories in the news that I haven’t covered.

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