The magnetocaloric effect with critical behavior of a periodic Anderson-like organic polymer

• Published in: Physical chemistry chemical physics : PCCP Vol. 18; no. 1; pp. 51 - 518
• Main Authors: Ding, L. J, Zhong, Y, Fan, S. W, Zhu, L. Y
• Format: Journal Article
• Language: English
• Published: England 07.01.2016
• Subjects: Collapse; Coupling; Entropy; Exponents; Ferromagnetism; Magnetization; Manganites; Orbitals
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c5cp06137g

We study the magnetocaloric effect and the critical behavior of a periodic Anderson-like organic polymer using Green's function theory, in which the localized f orbitals hybridize with the conduction orbitals at even sites. The field-induced metal-insulator transitions with the magnetic Grüneisen parameter showing | Γ h | ∼ T −1 power-law critical behaviour are revealed, which provides a new thermodynamic means for probing quantum phase transitions. It is found that the competition of up-spin and down-spin hole excitations is responsible for the double peak structure of magnetic entropy change (−Δ S ) for the dominant Kondo coupling case, implying a double magnetic cooling process via demagnetization, which follows a power law dependence of the magnetic field h : −Δ S ∼ h n . The local exponent n tends to 1 and 2 below and above T C , while has a minimum of 0.648 at T C , which is in accordance with the experimental observation of perovskite manganites Pr 0.55 Sr 0.45 MnO 3 and Nd 0.55 Sr 0.45 MnO 3 (J. Y. Fan et al. , Appl. Phys. Lett. , 2011, 98 , 072508; Europhys. Lett. , 2015, 112 , 17005) corresponding to the conventional ferromagnets within the mean field theory −Δ S ∼ h 2/3 . At T C , the −Δ S ∼ h curves with a convex curvature superpose each other for small V values, which are separated by the large V case, distinguishing the RKKY interaction and Kondo coupling explicitly. Furthermore, the critical scaling law n ( T C ) = 1 + ( β − 1)/( β + γ ) = 1 + 1/ δ (1 − 1/ β ) is related to the critical exponents ( β , γ , and δ ) extracted from the Arrott-Noakes equation of state and the Kouvel-Fisher method, which fulfill the Widom scaling relation δ = 1 + γβ −1 , indicating the self-consistency and reliability of the obtained results. In addition, based on the scaling hypothesis through checking the scaling analysis of magnetization, the M - T - h curves collapse into two independent universal branches below and above T C . The magnetic entropy change (−Δ S ) shows a double-peak structure, indicating a double magnetic cooling process via demagnetization.