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

Abstract

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 |Γh|∼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 (-ΔS) 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: -ΔS∼h(n). The local exponent n tends to 1 and 2 below and above TC, while has a minimum of 0.648 at TC, which is in accordance with the experimental observation of perovskite manganites Pr0.55Sr0.45MnO3 and Nd0.55Sr0.45MnO3 (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 -ΔS∼h(2/3). At TC, the -ΔS∼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(TC) = 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 TC.

An Analytical Approach for Computing the Coefficient of Refrigeration Performance in Giant Inverse Magnetocaloric Materials

“…Finally, Figure 5a-c depict the CRP vs. inverse CC slopes for an alloy with the same properties as the architype NiMnIn. The inverse CC slopes appear to have the greatest influence on the CRP out of all the material properties in Equation (25). This is not surprising, because the entropy change, or ∆𝑆 𝑀→𝐴 in Equation (19), depends on the inverse CC slope.…”

“…A wide range of crystalline and amorphous materials exhibit the MCE. Laves phases [20], ferromagnetic lanthanum manganites [21][22][23], and other rare-earth containing crystalline compounds [24][25][26][27] are commonly studied. Many Laves phase compounds, such as HoCo2 [28,29], TbCo2 [30], and TbFe2 [31], are of interest, because they exhibit a significant change in magnetization, M, across their ferromagnetic/paramagnetic Curie temperatures, T Curie .…”

Grüneisen ratio quest for self-duality of quantum criticality in a spin-1/2 XY chain with Dzyaloshinskii–Moriya interaction

“…The critical point that manifests a continuous phase transition falls into different universality classes in terms of their critical exponents, which are extracted from the singularity of various thermodynamic quantities near the critical point [3]. The self-consistency and reliability of the obtained critical exponents are further verified by the scaling hypothesis equations [3,4]. However, a different class of phase transition taking place at zero temperature, which is called quantum phase transition (QPT), has attracted much attention recently, which is purely driven by quantum fluctuations rooted in the Heisenberg uncertainty principle [1].…”

“…Of course, it was pointed out that the Güneisen ratio (GR) is an important tool to identify and testify a general QCP attributed to the powerlaw temperature dependence of divergence as well as sign change near the QCP [10][11][12], where the entropy is accumulated. It gives rise to strong signatures of GR near a QCP, which has been observed in heavy fermion metal [10], spin chains [5], metal-insulator transition systems [4] and so on. However, recently, it has been demonstrated by Zhang [9] that self-duality is a necessary condition for the nondivergence of GR at a QCP, in other words, nondivergent GR implies self-duality of the QCP.…”

Approach to control magnetic plateau in tetrameric magnetic systems

“…Low-dimensional quantum spin systems have received considerable attention in condensed matter physics [1][2][3][4][5][6][7][8][9][10][11][12]. In particular, one-dimensional Heisenberg spin chains with competing interactions show a variety of physical properties that have been widely studied both theoretically [7][8] and experimentally [9][10][11]13].…”