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Nature22 May 2003

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Condensed-matter physics: Spin chiller

Thermoelectric refrigeration systems, popular in microelectronics applications, were developed by NASA to cool spacecraft without the need for the bulky vibration-inducing compressors. Instead they depend on the Peltier effect, virtually a thermocouple acting in reverse. Thermoelectric refrigerators are reliable, as they have no moving parts, but could do with more power. The search for materials with high cooling capacity has been largely a matter of trial and error. But a new test of a theory to explain the electron interactions that produce thermopower could open up new avenues in the search for thermoelectric materials. Theory suggests that in materials such as transition metal oxides, the spins of electrons should account for a large fraction of the heat current. This has now been verified in the layered oxide compound NaxCo2O4. At low temperatures virtually all of the heat current is suppressed by a longitudinal magnetic field, so must derive from electron spin effects.

letters to nature
Spin entropy as the likely source of enhanced thermopower in NaxCo2O4
YAYU WANG, NYRISSA S. ROGADO, R. J. CAVA & N. P. ONG
Nature 423, 425–428 (2003); doi:10.1038/nature01639
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news and views
Condensed-matter physics: Thermopower to the people
CRONIN B. VINING
The larger-than-expected thermally generated voltage seen in a layered-oxide material — which may prove useful in power generation or cooling — is now attributed to the spins of moving charges.
Nature 423, 391–392 (2003); doi:10.1038/423391a
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