Episode 20: Samarium cobalt magnet fabricated with single-step method

In this podcast episode, MRS Bulletin’s Sophia Chen interviews Bharat Gwalani from North Carolina State University and Mert Efe from Pacific Northwest National Laboratory about their single-step, energy-efficient method for making a samarium cobalt magnet. Using a process they call “friction stir consolidation,” the researchers apply heat and pressure simultaneously to fuse the two powders together. Their method results in low porosity to make a magnetically stronger, higher quality material than that made by using the conventional method. This work was published in a recent issue of Nature Communications.

Transcript

SOPHIA CHEN: Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on hot topics in materials research. My name is Sophia Chen. Say you need a magnet that works at really high temperatures. Maybe you’re making a fancy high-end motor. It turns out you can’t use your typical neodymium iron boron magnet. These magnets start to significantly lose their magnetism in temperatures above 80 degrees Celsius. But a samarium cobalt magnet will probably do the trick. Samarium cobalt magnets retain their magnetism to around 250 degrees Celsius. But conventionally, it’s pretty complicated and energy-intensive to make them. Typically, you start with a crushed powder, which you have to heat and compact into a shape. You also apply an external magnetic field to align the domains to create magnets. In new work, materials researchers using machines at the Pacific Northwest National Laboratory and North Carolina State University have come up with a simpler, more energy efficient method for making these magnets.

BHARAT GWALANI: Our process, which we use, is called friction stir consolidation. We don’t have to then do any other additional steps. Single step, you can process it with lesser energy, because there is no melting, no disintegration and reintegration mold.

SOPHIA CHEN: That’s Bharat Gwalani, a materials researcher at North Carolina State University. His team’s technique uses a custom-built machine. Mert Efe, Gwalani’s collaborator at Pacific Northwest National Laboratory, describes how it works like this.

MERT EFE: First we compact the powder, so we put the powder in a circular die, we apply pressure, and we compact the powder, and then we load the powder in our machine. The tool comes in, it rotates on the powder, creates this friction, and then we apply the pressure at the same time, so there is heat and pressure at the same time, which helps to fuse these powders together. It’s similar to like pasta extruders. Have you seen like pasta extruded? So it’s very similar. But in this case, the dye rotates as well. That’s how we create the friction and heat in our case.

SOPHIA CHEN: Their process also avoids producing pockets of air in the magnet, which is common with conventional methods. These pockets of air lead to what’s known as high porosity in the magnet, which weakens its magnetism. Gwalani’s method results in low porosity to make a magnetically stronger, higher quality material.

BHARAT GWALANI: We don’t get pressure focused only in the periphery, and then less pressure or high porosity at the center of the magnet; the properties are uniformly distributed.

SOPHIA CHEN: The method also manages to get rid of certain common defects.

BHARAT GWALANI: When we purchase SmCo₅ powders, it comes with impurities, like another compound called Sm₂Co₇, which is not as magnetic as SmCo₅. Sm₂Co₇ is not desirable, but due to our process, we are able to convert that non-desirable product to a desirable product as well.

SOPHIA CHEN: In future work, they plan to apply an external magnetic field during the process to align the domains within the material to make its magnetism stronger. They’re also particularly excited about using the technique to create magnets composed of multiple materials, such as samarium cobalt and another metal like zinc or aluminum, or a ceramic. This gives them a way to create magnets tailored for specific applications, such as with customized mechanical properties, for example. 

MERT EFE: We are obtaining magnetism and strength at the same time, or magnetism and ductility at the same time. So essentially, we are developing a new class of composites.

SOPHIA CHEN: This work was published in a recent issue of Nature Communications. My name is Sophia Chen from the Materials Research Society. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on X, @MRSBulletin. Don’t miss the next episode of MRS Bulletin Materials News – subscribe now. Thank you for listening.