The Defense Department is buying $400 million of stock in rare-earth mining company MP Materials as it seeks to boost domestic sources of the critical minerals.

The deal would see the Defense Department take a 15% stake in MP Materials and spend billions of dollars investing in the company and purchasing its output.

Shares of Australian rare earths miners, including Lynas and Iluka Resources , soared on Friday after U.S.-based MP Materials' a multibillion-dollar deal with the U.S. government to boost production of rare earth magnets.

The money will fund the construction of a new domestic magnet-manufacturing facility and the expansion of MP Materials’ current mining and processing capabilities. “Rare earth magnets are one of the most strategically important components in advanced technology systems spanning defense and commercial applications,