Department of Physics & Astronomy
Louisiana State University
202 Nicholson Hall
Baton Rouge, LA 70803
The ever-increasing global consumption of limited energy resources such as fossil fuels, and its related impact on the environment, has stimulated a widespread effort to develop cleaner and more energy-efficient technologies. A large fraction of energy is consumed in cooling operations, including food preservation and environmental air conditioning, and therefore improvements beyond existing refrigeration technologies would have a significant impact on energy conservation. One potential leap in this technology is magnetic refrigeration based on the magnetocaloric effect (MCE), owing to its potentially negligible environmental impact and high efficiency. The discovery of a material that exhibits a large magnetocaloric effect over a wide temperature range spanning room temperature would revolutionize the refrigeration industry.
The magnetocaloric effect (MCE) is defined as a reversible, magnetic-field-induced temperature change in a magnetic material. The discovery of the effect is credited to E. Warburg for his observation of the phenomenon in pure iron in 1881. One of the original applications of the MCE was formulated by William F. Giauque in 1927 (the actual experiment was carried out in 1933) in the adiabatic demagnetization of paramagnetic salts to achieve temperatures below one Kelvin, resulting in the Nobel Prize in Chemistry in 1949. [2,3] For the next few decades, the MCE was primarily employed in low temperature physics until the mid-1970’s, when Brown developed a near-room-temperature magnetic refrigerator that exploited the phenomenon in metallic gadolinium.  The engineering aspects of gadolinium-based refrigerators, as well as those employing other working materials, have been aggressively developed ever since. [5,6]
A typical refrigeration cycle: (1) The magnetocaloric material is magnetically disordered and at ambient temperature. (2) The material is magnetically ordered, and its temperature increases. (3) The temperature of the sample is reduced using a heat exchange method (fluid or air flow), and (4) the material is now magnetically ordered and at ambient temperature. (5) The material is removed from the field, becomes magnetically disordered, and now has a temperature below the ambient. It can now be used to cool a load.