Consequences of the magnetocaloric effect on magnetometry measurements

Magnetization curves recorded at high sweep-rates on magnetic materials near a phase transition temperature can be affected by temperature changes in the material due to the magnetocaloric effect. This change in the sample temperature is a result of the quasiadiabatic conditions that can occur under such conditions and we demonstrate its effects on magnetization curves of two magnetocaloric materials, La(Fe0.945Co0.055)(11.9)Si-1.1 and Gd5Si2Ge2. We show how a quantity calculated from isothermal magnetization curves, the magnetic entropy change, Delta S-M, is affected by the erroneous data. As Delta S-M is a measure of the magnetocaloric effect, the discrepancies demonstrated here are more severe close to a peak in Delta S-M, which is precisely the quantity that is of interest and reported on in the literature from possibly erroneous magnetization data. We also demonstrate how, through simple measurements and without a direct measurement of the sample temperature, one can determine an appropriate sweep-rate of the magnetic field. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3466977]