BAOTOU, China — China’s strict controls on the export of heat-resistant magnets made with rare earth minerals have exposed a major vulnerability in the U.S. military supply chain.

Without these magnets, the United States and its allies in Europe will struggle to refill recently depleted inventories of military hardware.

For more than a decade, the United States has failed to develop an alternative to China’s supply of a specific kind of rare earth crucial for the manufacture of magnets for missiles, fighter jets, smart bombs and a lot of other military gear.

Rare earth minerals are a central issue in the trade talks between the United States and China now underway in London.

China Produces Entire World’s Supply of Samarium

China produces the entire world’s supply of samarium, a particularly obscure rare earth metal used almost entirely in military applications. Samarium magnets can withstand temperatures hot enough to melt lead without losing their magnetic force. They are essential for withstanding the heat of fast-moving electric motors in cramped spaces like the nose cones of missiles.

On April 4, China halted exports of seven kinds of rare earth metals, as well as magnets made from them. China controls most of the world’s supply of these metals and magnets. China’s Ministry of Commerce declared that these materials had both civilian and military uses, and any further exports would be allowed only with specially issued licenses. The move, according to the ministry, would “safeguard national security” and “fulfill international obligations such as nonproliferation.”

The ministry has begun issuing some licenses for magnets that include two of the restricted rare earths, dysprosium and terbium, to automakers in Europe and the United States. Magnets with these two rare earths, which are used in brake and steering systems, can withstand the heat of a nearby gasoline engine but cannot reliably tolerate the greater heat encountered in military applications. But there has been no sign that China has approved exports of samarium, which has few civilian applications.

Chinese and U.S. officials began two days of trade talks in London on Monday. Restoring the flow of rare earths is a priority for U.S. officials, but few expect China to rescind its new export license system entirely.

“I don’t think that’s going away,” said Michael Hart, the president of the American Chamber of Commerce in China, who is coordinating the U.S. private sector’s efforts in Beijing to obtain more rare earth materials.

The main American user of samarium is Lockheed Martin, an aerospace and military contractor that puts about 50 pounds of samarium magnets in each F-35 fighter jet. Lockheed Martin responded to questions with a short statement: “We continuously assess the global rare earth supply chain to ensure access to critical materials that support our customers’ missions. Specific questions about the rare earth supply chain will be best addressed by the U.S. government.”

Officials in the Biden administration were so concerned about the U.S. military’s lack of a domestic samarium supply that they issued large contracts for the construction of two samarium production facilities. Neither was built because of commercial concerns, leaving the United States entirely dependent on China.

United States, Europe Rush to Rebuild Inventories of Advanced Weapons

The interruption in samarium supplies over the past two months comes as the United States and its allies in Europe are rushing to rebuild inventories of advanced weaponry. These stocks have been severely depleted by shipments to Ukraine after the Russian invasion and, for the United States, to Israel during the conflict in the Gaza Strip.

The Trump administration is also trying to supply more weapons to Taiwan, an island democracy over which Beijing claims sovereignty. In addition to halting exports of rare earths for military use, China recently imposed sanctions on some American military contractors because of their roles supplying Taiwan.

Those sanctions now bar Chinese companies and individuals from having any financial connection to the U.S. military contractors. That did not have much of an effect on the samarium industry until recently, because China exported samarium to chemical companies that mixed the metal with cobalt before selling it to magnet manufacturers, which then sell to the military contractors.

But Beijing’s new export controls on rare earths specify that licenses can only be issued based on the final user of the mineral at the end of the supply chain. For samarium licenses, that sometimes means military contractors.

Of the seven kinds of rare earth metals restricted by China, the demand for six of them is largely civilian, said Stanley Trout, a metallurgist at the Metropolitan State University of Denver who has specialized in samarium magnets since the 1970s.

Samarium is different. It is “almost exclusively used for military purposes,” he said.

U.S. Defense Department regulations require that the casting or smelting of military magnets be done in the United States or a friendly nation. But the rules allow the ingredients of military magnets to be imported from anywhere, so low-cost samarium has come from China for many years, Trout said.

Concerns About Dependence on China for Samarium

Concerns about dependence on China for samarium are not new. Starting in the 1970s, militaries in the West depended on a single chemical factory in La Rochelle, France, that refined samarium from ore mined in Australia. But that factory closed in 1994, partly because of pollution concerns. The factory also could not compete with inexpensive production in Baotou, a city in China’s Inner Mongolia region with a history of weak environmental enforcement, even by China’s standards.

In 2009, U.S. lawmakers became worried about American dependence on samarium supplies from refineries in Baotou, a flat, dry industrial city at the southern edge of the Gobi Desert. Congress ordered the Defense Department to come up with a plan by the following year to address the issue.

That was before China halted shipments to Japan of all 17 kinds of rare earths for two months in late 2010 as part of a territorial dispute. A $1 billion American effort began soon after to repair, expand and reopen the sole U.S. rare earths mine, in Mountain Pass, California, which had suspended operations in 1998 following a pipeline leak.

Rare earth metals are found all over the world, but seldom in concentrations high enough to allow for efficient mining. They are tightly bound together, and breaking those chemical bonds can require a sequence of 100 or more chemical processes using extremely powerful acids.

The Mountain Pass mine had not previously tried to pry samarium loose from its ore, and did not start doing so as part of its expansion. The mine reopened in 2014, producing other rare earths, but closed a year later and went bankrupt because it could not compete with Chinese production.

Jay Truesdale, a former American diplomat who played a senior role at the State Department on critical minerals policy in 2014 and 2015, said the focus during the Obama administration had been on using World Trade Organization rules to compel China to sell its rare earths.

“There was less of an alarmist perspective at that time, because the WTO was seen as the right and proper arbiter of these issues,” said Truesdale, who is now CEO of TD International, a Washington consulting firm.

During his first term, President Donald Trump considerably reduced U.S. participation in the WTO, and relations with China worsened. When the Biden administration took office, senior officials became more concerned about samarium.

A new company, MP Materials, had acquired the Mountain Pass mine and resumed operations there in 2018. But it initially shipped ore to China for processing.

The Defense Department awarded $35 million to MP in early 2022 to start production of samarium and several other rare earths that China has now restricted. MP then spent $100 million, using a lot of its own money, to buy the necessary equipment to process them, said James Litinsky, the company’s CEO.

The Biden administration soon after awarded $351 million to Australia’s Lynas Rare Earths to build a facility in Texas that would also produce samarium.

Litinsky said that the market for samarium is so small that it would be uneconomical to have two producers in the United States. So MP never installed its samarium processing equipment, which is still in storage.

But Lynas never built its Texas factory, after a permit it had for rare earth mining in Malaysia that was in limbo was eventually renewed. Lynas did not respond to emails and phone calls for comment.

MP is only willing to install its samarium processing equipment now if promised better financial terms by customers, Litinsky said. “We felt very burnt by the whole thing.”

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This article originally appeared in The New York Times.

By Keith Bradsher
c. 2025 The New York Times Company