ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Study of the thermodynamics of magnetic refrigeration cycles that use the magnetocaloric effect in ferromagnetic materials requires, as a minimum, knowledge of the zero-field heat capacity C0 and the equation of state of the magnetization, M= f(B,T), for each material. However, refrigerator design calculations are easier to make if the field-dependent heat capacity CB and adiabatic temperature change ΔTS are known. The field-dependent heat capacity can either be directly measured or be derived according to CB(B,T) =CB(B=0,T) + ∫B0 (∂2M/∂l2)dB. The adiabatic temperature change can be obtained in three ways: by direct measurement, from field and temperature dependent entropy curves, or from dT=−T ∫B0 (1/CB) (∂M/∂T)dB. The time required for measurement, the complexity of the apparatus, and the quality of the resultant data differ considerably among the above methods. We have measured the magnetization, heat capacity, and adiabatic temperature change for several ferromagnetic intermetallic gadolinium compounds. Using these data an analysis of the different methods of obtaining CB and ΔTs will be presented. The accuracy, precision, and pitfalls of each approach will be discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.334934
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