Story by BERND SCHRÖDER
When you put things inside a magnetic field, the outcome can be surprising. In some ferromagnetic materials, for example, the temperature changes — a phenomenon called the magnetocaloric effect. Gadolinium sets a benchmark: The rare-earth element exhibits a significant magnetocaloric effect in relatively low fields. When gadolinium is placed in a magnetic field of 2 teslas — about the strength of the magnet in an average MRI machine — its temperature jumps by about 5 degrees Celsius.
What would happen if you put the silvery metal in much higher fields? Physicists from the Dresden High Magnetic Field Laboratory at the Helmholtz-Zentrum Dresden-Rossendorf in Germany decided to look into it.
The scientists had the right tools to tackle the question. The lab is home to some of the world's strongest pulsed magnets, which are electromagnets that generate fields so powerful they only last a few milliseconds. But measuring behavior that happens in the blink of an eye can be tricky.
"This is where the biggest challenge lurks for everyone trying to measure this effect: Developing a method that accurately records the temperature change during the brief experiment," said Tino Gottschall, the lab's lead scientist. "To do this, we applied miniaturized thermocouple wires, half as thick as a human hair."
With that unique setup, the scientists detected a whopping 60.5 degrees Celsius temperature change in gadolinium in a 62-tesla field. Just as spectacular, research team members from the Aix-Marseille University in France developed a mathematical model neatly describing the effect.
In the future, materials with magnetocaloric properties could be used in magnetic cooling devices, offering a more sustainable alternative to classical refrigeration. But these devices probably won't be made with gadolinium, which is expensive. Still, this "gold standard” material for magnetocaloric properties could help us better understand the phenomenon in other materials. Already, the team behind this project (which included researchers at Ames Laboratory in the U.S. and TU Darmstadt in Germany) is planning to study other rare-earth elements in pulsed fields.