July 05, 2010

Lawrence Berkeley Labs Preforms Basic Research Towards Energy Saving Magnetic Fridges

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Fundamental research conducted at facilities like Berkeley Lab's Advanced Light Source could lead to the energy-saving technologies of tomorrow, such as a magnetic fridge. Jeff Kortright (left) and Sujoy Roy with an an endstation for soft x-ray resonant magnetic scattering and spectroscopy, which the scientists used at the Advanced Light Source's beamline 4.0.2 to learn more about the magnetocaloric effect in alloys. (Image by Roy Kaltschmidt, Berkeley Lab Public Affairs)
The idea is to use a material that exhibits a giant magnetocaloric effect, and use it as a refrigerant, like a high-tech block of ice. The giant magnetocaloric effect is where a changing magnetic field in a material causes its temperature to drop precipitously

“It’s a very promising concept. But to make it a reality, we first must learn in detail what’s happening inside materials as they undergo the giant magnetocaloric effect,” says Sujoy Roy, a physicist with Lawrence Berkeley National Laboratory.

Delocalization and hybridization enhance the magnetocaloric effect in Cu-doped Ni2MnGa

The structural and magnetic transitions in the shape-memory alloy Ni2MnGa can be tuned as a function of temperature by adding dopants. By altering the free energy such that the structural and magnetic transitions coincide, a giant magnetocaloric effect is created near room temperature. We show, using x-ray absorption spectroscopy and x-ray magnetic circular dichroism, how Cu, substituted for Mn, pulls the magnetic transition downward in temperature and also, counterintuitively, increases the delocalization of the Mn magnetism. At the same time, this reinforces the Ni-Ga chemical bond, raising the temperature of the martensite-austenite transition. At 25% doping, the two transitions coincide at 317 K.


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