科研之友
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摘要
The Maxwell relation, the Clausius-Clapeyron equation, and a non-iterative method to obtain the critical exponents have been used to characterize the magnetocaloric effect (MCE) and the nature of the phase transitions in Pr0.5Sr0.5MnO3, which undergoes a second-order paramagnetic to ferromagnetic (PM-FM) transition at T-C similar to 247 K, and a first-order ferromagnetic to antiferromagnetic (FM-AFM) transition at T-N similar to 165 K. We find that around the second-order PM-FM transition, the MCE (as represented by the magnetic entropy change, Delta S-M) can be precisely determined from magnetization measurements using the Maxwell relation. However, around the first-order FM-AFM transition, values of Delta S-M calculated with the Maxwell relation deviate significantly from those calculated by the Clausius-Clapeyron equation at the magnetic field and temperature ranges where a conversion between the AFM and FM phases occurs. A detailed analysis of the critical exponents of the second-order PM-FM transition allows us to correlate the short-range type magnetic interactions with the MCE. Using the Arrott-Noakes equation of state with the appropriate values of the critical exponents, the field-and temperature-dependent magnetization M(T, H) curves, and hence the Delta S-M(T, H) curves, have been simulated and compared with experimental data. A good agreement between the experimental and simulated data has been found in the vicinity of the Curie temperature T-C, but a noticeable discrepancy is present for T%26lt;%26lt;T-C. This discrepancy arises mainly from the coexistence of AFM and FM phases and the presence of ferromagnetic clusters in the AFM matrix.
- 出版日期2014-7-26
