Second-Order Phase Transition and the Magnetocaloric Effect in }}} Nanoparticles

In this paper, we present a detailed study of the magnetocaloric effect and critical properties around the ferromagnetic-paramagnetic (FM-PM) phase transition of La 0.7 Ca 0.3-x Sr x MnO 3 nanoparticles with x = 0.10, 0.11, and 0.12. The samples were synthesized by a combination of reactive milling...

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Bibliographic Details
Published in:IEEE transactions on magnetics 2014-04, Vol.50 (4), p.1-4
Main Authors: Tran Dang Thanh, Phan, T. L., Nguyen Van Chien, Do Hung Manh, Yu, S. C.
Format: Article
Language:English
Subjects:
Compounds
Crystallites
Diffraction
Entropy
Frequency modulation
Magnetic fields
Magnetic properties
Magnetic resonance imaging
Magnetism
Materials
Metals
Nanoparticles
Phase transformations
Phase transitions
Three dimensional models
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Summary:In this paper, we present a detailed study of the magnetocaloric effect and critical properties around the ferromagnetic-paramagnetic (FM-PM) phase transition of La 0.7 Ca 0.3-x Sr x MnO 3 nanoparticles with x = 0.10, 0.11, and 0.12. The samples were synthesized by a combination of reactive milling and thermal processing. The average crystallite size of nanoparticles estimated from the linewidth of X-ray diffraction peaks by using the Williamson-Hall method is about 50 nm. Under a magnetic field change of 10 kOe, the maximum magnetic entropy change (|ΔS max |) reaches values of 1.47, 1.42, and 1.38 J·kg -1 ·K -1 for x = 0.10, 0.11, and 0.12, respectively, at around 300 K. The refrigerant capacity is thus in between 44 and 54 J·kg -1 . Particularly, the M 2 versus H/M curves prove that all the samples exhibit a second-order magnetic phase transition. Based on Landau's phase-transition theory and careful analyses of the magnetic data around the FM-PM transition region, we have determined the critical exponents β, y, δ, and T C . Here, the β values obtained are 0.397, 0.453, and 0.456 for x = 0.10, 0.11, and 0.12, respectively, which are in between those expected on the basis of the mean-field theory (β = 0.5) and value of the 3-D Heisenberg model (β = 0.365). The result proves the coexistence of shortand long-range FM interactions in La 0.7 Ca 0.3-x Sr x MnO 3 nanoparticles. The nature of this phenomenon is discussed thoroughly.
ISSN:0018-9464
1941-0069
DOI:10.1109/TMAG.2013.2288410