ABSTRACTUpon the application of an external magnetic field, the magnetic spins in a material partially align with the field, thereby reducing the magnetic entropy of the spin system. When performed adiabatically, the specimen's temperature will rise. This temperature rise, δT, related to the entropy change by the heat capacity, is known as the magnetocaloric effect. Upon cycling the magnetic field, this effect can be used for transferring heat from one thermal reservoir to another, forming the basis for a magnetic refrigerator. Recently, NIST scientists predicted composite magnetic materials containing nanometer-size magnetic species could possess enhanced magnetocaloric effects [1-2], especially at high temperatures or low magnetic fields. Magnetic nanocomposites may be prepared in many different ways, and recent magnetocaloric effect data measured on Fe-doped gadolinium gallium garnets are presented to show both the effect of processing and a methodology for optimizing δT.