How Magnetic Cooling Is Breaking All the Rules

Author: Matt Ferrell

What if I told you your fridge — that humming box in the kitchen — could be cooled without gas, without chemicals … just magnets? It sounds futuristic, but researchers are already making it happen. It not only promises higher efficiency, but solves a critical problem with the status quo…yes, a critical problem that plagues even my beloved heat pumps.

The thing is, we need an alternative to refrigerants. Caloric cooling is one alternative, and one U.S. research team claims that magnetocalorics in particular are already on their way to replacing our current coolants with systems that are much more…attractive. But how do you control the temperature with a solid material rather than a refrigerant gas? What makes magnetocalorics stand out? And is this cooling tech solid enough to redefine what it means to be a “fridge magnet”?

Magnetocalorics may not be mainstream, but they’re not moving at a glacial pace. A few new commercial products have already hit the market that cool with magnetocalorics. One German company is already selling a beverage cooler and offering pre-orders for a two-door commercial refrigerator.¹² At the end of last year, you could grab yourself a drink out of a functioning fridge displayed by a French-German company at a heating and cooling technology trade fair. Shortly after that, a major research update came from the Ames National Laboratory in the U.S. that kicked off our investigation into this topic.

This is our second dive into the world of caloric cooling—so if you caught our earlier video on elastocalorics, some of this might ring a bell. But I promise, there’s a very big material difference at hand here. Instead of stretching the limits of refrigeration tech with rubber, today we’ll talk about how researchers have been throwing magnets at the wall…to see what sticks.

The vapor compression cycle behind our freezers and HVAC systems is centuries old.³ At its core, it’s all about phase changes—nature’s clever trick that lets 5 billion heat pumps, fridges, and ACs shuffle heat around to keep us comfortable.⁴⁵⁶ But as elegant as that system is, it relies heavily on refrigerants—mostly hydrofluorocarbons, or HFCs—that change phase throughout the cycle. And as you probably know, HFCs come with some serious environmental baggage. It’s clear our approach to climate control could use an upgrade—and swapping refrigerants for magnets might be just the retooling we need.

Vapor compression

To understand the greater study of caloric cooling, we first have to understand what we’re working with. If you weren’t around for our first exploration into “caloric effects,” or maybe your memory has just vaporized, here’s a compressed refresher.

Our current generation of cooling units—whether it’s a window AC or an old-school iceboxe—are all heat exchangers. A heat exchanger is just a machine that moves heat from a hotter place to a cooler one.⁷⁸ Most cooling devices rely on four main components: a compressor, condenser, expander, and evaporator.⁴ These make up the vapor-compression cycle, which breaks down into four key steps:

1. First up, the compressor—it boosts the temperature and pressure of the refrigerant vapor.
2. Then the condenser kicks in, turning that vapor into a liquid and releasing heat in the process.
3. Next, the expander drops the pressure of the refrigerant. As it expands, it cools down—colder than the space we want to chill.
4. Finally, the evaporator absorbs heat from the surrounding area, vaporizing the refrigerant.

And just like that, the cycle repeats, with the compressor grabbing that warm vapor and starting all over again.^94101112

Now you can confidently explain how your fridge works—perfect the next time you need a cool icebreaker. But this method is everywhere. Given that vapor compression dates back to the 19th century, it’s fair to say our refrigerators have been running strong for a long time.³ So… how could magnets possibly catch up and improve on that?

Magnetocalorics

Magnetocalorics, or magnetic cooling, have been an ongoing field of study for researchers interested in dumping refrigerants. Er, or maybe no longer having to worry about the consequences of dumping refrigerants. Anyway, scientists have tinkered with the concept of magnetic refrigeration for decades. The reason why magnetocalorics is suddenly attracting attention, however, is partly due to recent prototypes that research teams claim have achieved parity with existing vapor compression models.¹³

How is this possible? Lucky for us, this process can also be broken down into four steps, just like the vapor compression cycle. In fact, all forms of caloric cooling parallel the vapor compression cycle. A hypothetical HVAC based on caloric effects would…effectively…be substituting refrigerants for any material that, when manipulated, changes temperature. You start with a caloric material, which could be anything from rubber to ceramic, as opposed to a gaseous refrigerant.¹⁴ Then you apply force. No, really.

In our previous video on the topic, I showed off the elastocaloric effect, which is based on mechanically stressing — in other words, bending — a material like these nitinol wires. (And guess what, kids? You can try this at home!) Just like refrigerants, elastocaloric materials undergo phase changes that alternatively cool them down and heat them up.

But caloric cooling doesn’t always need physical force. As opposed to mechanical stress, electrocaloric devices expose certain materials to electric fields so that they change phases. You can probably tell where I’m going with this: magnetocalorics involves subjecting the right kind of material to a magnetic field to accomplish the same thing.

So, what is the “right kind” of material? Magnetocaloric cooling may be a marvel, but we won’t be needing any telepathy-blocking helmets to get the desired effect. Store-bought magnetism is fine. Let me introduce you to gadolinium: neutron poison, friend to radiologists, and the 64th element in the periodic table.¹⁵ While you might already know the metal for its applications in keeping nuclear reactors under control and scanning our brains, it also has the potential to develop into something that’s a lot more…domestic. That’s because gadolinium is one blade in our magnetocaloric multitool. In other words, gadolinium is one of the most common materials that these devices can apply magnetic fields to.

Ames Lab MCHP

What does that look like in practice? I’ll answer that question by taking you through the inner workings of a device newly developed by the U.S. Department of Energy Ames National Laboratory. In December 2024, the Iowa State University research team, lead by Julie Slaughter, announced the completion of a magnetocaloric heat pump (or MCHP) that they claim can match “current vapor-compression heat pumps for weight, cost, and performance.”¹⁶

For this particular iteration, the research team studied the magnetocaloric effects of both gadolinium and LaFeSi, an alloy of lanthanum, iron, and silicon. We’ll get into why LaFeSi matters later, though. To start, the Ames Lab team created their “baseline device” using gadolinium. So, let’s map out exactly where and how it does its thing.¹³

Inside the middle of the heat pump’s cylindrical housing lies the active magnetic regenerator, or AMR.¹³ If you’re unfamiliar, don’t let the acronym intimidate you…like it initially did me. A regenerator is just another type of heat exchanger in the broader family tree.⁸

What makes regenerators different than other types of heat exchangers is that both the hot and cold streams cross over the same paths.¹⁷⁸ But their goal is the same as any other: get that heat away from the hot area, and bring it to the colder one. As for what “active magnetic,” means, the basic concept is that magnetic material plays two roles, as both the foundation for the regenerator and the stand-in for the refrigerant itself.¹⁸¹⁹

The Ames model AMR consists of nine “beds” arranged into a ring. The AMR is porous — not unlike a foam mattress, actually. These hold a bunch of tightly-packed gadolinium particles, each only about 200 microns across…so about the size of a very fine coffee ground.²⁰¹³ At the start of the regenerative cycle, these particles are demagnetized…or not-yet-magnetized, more precisely. They’re kind of … well … asleep in these beds.

Speaking of coffee, you know how some people can’t function in the morning until they’ve had their coffee? Well, if you think about it you could call coffee a “working fluid.” It’s definitely conducive to working. Magnetocaloric devices just tend to prefer a steaming cuppa of water instead, typically with a little shot of something extra for practical flavor. The Ames prototype will have its working fluid with one pump of anti-corrosion agent, please. (Or at least, that’s what lead author Julie Slaughter confirmed via email.) While I don’t think you’ll be able to order this drink off a secret menu any time soon, it gets a very important job done: it flows into the AMR beds hot and ready to begin the cooling process.

Even with a “don’t even talk to me until…” mug in hand, the gadolinium particles are still disorderly. To jolt them upright and activate them, you need a magnetic field. That’s where a set of permanent magnets step in. And by “step in,” I really mean “spin in,” because in the Ames heat pump, these magnets are set into a central circuit that rotates. As they pass by each stationary AMR bed, the gadolinium magnetizes and gets hot. Then, as the magnetic field moves over to the next bed, that array is no longer exposed to it, and it loses its magnetization. This causes the the gadolinium temperature to drop and get cold, similar to what happens when you depressurize of a gas refrigerant in a traditional compressor.¹³

From there, the working fluid cools, then moves to the hotter end of the heat pump’s internal core. The setup demagnetizes, and the cycle starts again…for the individual bed, that is. The cool thing about this arrangement is that because the magnets are rotating, they’re constantly magnetizing and demagnetizing each bed in turn…and therefore alternatively heating and cooling them off.¹³ Here’s what that looks like in action:

Of course, the Ames Lab research team did not invent this approach. In fact, the other magnetocaloric devices we’ll show off in this video also work using a rotating circuit. The focus of Ames study wasn’t the design of the prototype: it was its optimization. Remember that other magnetocaloric material, LaFeSi? Once the researchers got the initial design with gadolinium down pat, the goal was to improve the system power density, or SPD. As explained in the paper, SPD is “thermal power in watts divided by device mass in kilograms,” which is a quick way to compare magnetocaloric heat pumps with compressors.¹³ So, power divided by mass, or basically: bang for your buck. After all, it isn’t that magnetocaloric heat pumps haven’t been proven to work. It’s that — just like earlier iterations of computers — they’re currently too big and therefore too expensive for home use.¹³ Less bulk = lower price.

Part of the Ames Lab’s efforts in increasing SPD not only came down to finding the best way to align the permanent magnets and the AMR beds, but also figuring out how much material they could cut down on and the best materials to use. The team’s analysis projected that by just swapping gadolinium with LaFeSi, the SPD shot up without even having to modify anything else. In their words, using LaFeSi could allow MCHPs to become competitive with typical cooling devices “up to 1 kW of cooling power,” leaving cost parity “within reach.”¹³

Magnoric

The Ames Lab isn’t done yet, though. By the researchers’ estimate, it’ll be another three to six months before the performance evaluation for this iteration of their MCHP is complete. In the meantime, you can find researchers exploring magnetocalorics on the more commercial side in Europe. The French-German startup Magnoric, headquartered in Duppigheim and operating since 2019, is at work developing a refrigeration prototype.

In October 2024, Magnoric debuted its magnetocaloric display cabinet at Chillventa, a heating and cooling tech trade fair.²¹ The company not only showed off how the refrigerator works, but proved its mettle by handing out cold drinks kept inside it.²²

In a press release for the event, Magnoric explained that it’s “now entering the pre-industrialization phase for larger units exceeding 6 kW.” These are for big use cases with high demand, like supermarkets and data centers.²³ But even Magnoric itself is clear that as effective as magnetocalorics are, they’re still in the research phase — though the company says “industrialization is imminent.”²⁴

Magnotherm

And that claim doesn’t seem to be too far off, because Magnoric isn’t the only European company bringing magnetocaloric refrigeration to the forefront. A short drive away from Magnoric’s HQ lies Magnotherm in Darmstadt, Germany. These two companies may share similar names and the same founding year, but what sets Magnotherm apart is its catalogue. You can already get your hands on its magnetocaloric chiller for a cool €6,500 (or about $7,000).² Then there’s the company’s Eclipse model, a two-door glass case with clearly laid-out specs.

However, as you’ve probably noticed, both Magnotherm and Magnoric are targeting commercial industries. You can’t exactly store your Thanksgiving turkey in Magnotherm’s Polaris cooler, and the Eclipse, like Magnoric’s prototype, is for large-scale applications: retail, hospitality, and medicine.¹ That just goes back to the whole point of the Ames Lab research: determining the best way to make magnetocaloric devices cheaper and more compact, and therefore more practical. As of right now, cost is the age-old barrier to picking up a magnet-powered fridge or heat pump at a hardware store.

For those of you who have already seen our video on elastocalorics, you might still have a lingering question: why invest in magnets? Research indicates that elastocalorics specifically have already beaten out magnetocalorics in terms of performance, sort of just by nature. It’s easier to apply stress to something than it is to control a magnetic field.¹⁰ You also have to consider how permanent magnets are already highly sought after goods in the renewables industry alone — not to mention their other applications.²⁵ As written in a 2023 paper on elastocalorics:

“Magnetocaloric materials and devices have been explored for almost 50 years, with kilowatt-range cooling power refrigeration systems being demonstrated. Their high magnetic field requirement (>1 T) has, however, hampered commercialization.”²⁵

Of course, not everything elastic is fantastic. Magnoric’s argument is that elastocalorics, while highly efficient and quiet, have to contend with more limited lifespans until researchers figure out how to either preserve or improve the durability of elastocaloric materials.²⁴ Stressing components further breaks them down, even when the cool results of that stress is what you want. We go in-depth into these challenges in our first video and my follow-up interview with University of Maryland elastocalorics researcher Ichiro Takeuchi.

There’s also the fact that elastocalorics are the baby of the solid-state cooling house.²⁴ Interest in the tech is very much new, especially compared to its magnetic older sibling.²⁵ By the time this video publishes, the International Elastocaloric Society’s second conference won’t even have happened yet. So, you could say magnetocalorics have the maturity advantage here.

At the end of the day, though, any cooling device that can function without refrigerants is critical to the progress of the clean energy transition. It promises both better efficiency and fewer risks to human and environmental health. And if nothing else, the concept of solid-state cooling is a real gas.