Anomalous barocaloric effect in solid magnetic materials

Abstract

In this paper, we systematically discuss the barocaloric effect in solid magnetic materials undergoing both second and first order phase transition. For this purpose, we use a model of localized magnetic moments, including the magnetoelastic coupling and the Zeemann interaction. Our calculations show that the normal (inverse) barocaloric effect occurs whenever the applied pressure increases (decreases) the critical temperature and keeps the order of the phase transition. On the other hand, our calculations predict an anomalous barocaloric effect (i.e. a change of sign in the barocaloric potentials) in special cases where the applied pressure changes the phase transition from first to second order and vice versa.

Theoretical investigation on the barocaloric and magnetocaloric properties in the Gd5Si2Ge2 compound

“…It is worth noticing that the first order phase transition in our model is governed by J 1 parameter. 8,9,26 This result agrees with our model, since increasing pressure decreases the thermal hysteresis due to magnetoelastic interaction decreasing, see J 1 FIG. 3.…”

“…In this scenario, the barocaloric potentials are DS bar T > 0 and DT bar ad < 0. 8,9 In 1997, the giant magnetocaloric effect (GMCE) was discovered in the Gd 5 Si 2 Ge 2 compound. 10,11 This discovery has renewed interest in the research for materials exhibiting similar caloric effects 12 (barocaloric, eletrocaloric, elastocaloric, etc.).…”

Origins of the Inverse Electrocaloric Effect

“…First the barocaloric effect is related to hydrostatic pressure ∑ i = j σ ij =− p , which couples to the fractional volume change V ′=Δ V V −1 ( F = U − TS − E ⋅ P + pV ′). Inverse barocaloric effects were reported for various materials . In particular, as measured directly in Ref.…”

“…Inverseb arocaloric effects were reported for variousm aterials. [86][87][88][89][90][91][92] In particular, as measured directly in Ref. [90],B aTiO 3 ceramicss how an inverse barocaloric effect at the T-O and T-C phase transitions.A tb othp hase boundaries,t he high-temperature phase with highere ntropy has as maller volume.T hus,b ya pplying an external pressure one can induce at ransition to the "high-entropy"p hase and the entropy increasesw ith the latent heat of the transition in analogy to the discussion of the inverse ECE in Section 3.1.2.…”

Free-energy analysis of the nonhysteretic first-order phase transition of Eu2In

“…Increasing D beyond a certain critical value D C at fixed λ leads to a higher magnetic transition temperature T C ; hence in the model T C becomes dependent on both D and λ. We note that for a given λ when D < D C the transition at T C is second order, and it becomes first order when D > D C [26][27][28]. The associated phase volume change is included in the model through a change in the Debye temperature θ D :…”