Multicaloric effect in a solid: New aspects

Abstract

The multicaloric effect that is the result of interaction between various caloric effects has been studied theoretically. The effects attributable to the pairwise interactions of fields (piezomagnetocaloric, piezoelectrocaloric, and magnetoelectrocaloric effects) have been added to the previously known electroca loric, magnetocaloric, and elastocaloric effects that exist when the electric, magnetic, and elastic fields change. These new effects are shown to be determined by the temperature dependence of the piezomagnetic (magnetostrictive), piezoelectric (electrostrictive), and magnetoelectric coefficients. According to the esti mates obtained, the change in entropy in an isothermal process under the magnetoelectrocaloric effect for Cr 2 O 3 is 2-5 mJ kg -1 K -1 . The caloric effects caused by the influence of the gradient in one of the fields on other fields are shown to contribute to the multicaloric effect. One of these gradient effects, the flexocaloric one, which consists in a change in temperature and/or entropy when a strain gradient is applied or removed, has been studied in detail as an example. It follows from the derived formulas that the greatest values of this effect should be expected for materials with strong temperature dependences of the flexocaloric coefficient, permittivity, or permeability. The change in temperature calculated from experimental data for a PMN fer roelectric is estimated as 2-6 mK at a strain gradient of 1 m -1 . The interaction between fields of a different nature is known to lead to the synergetic effect, and the multicaloric effect can reach values that are com monly called giant ones, expanding considerably the possible domains of its application.

Strain assisted electrocaloric effect in PbZr0.95Ti0.05O3 films on 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 substrate

“…Recently, a theoretical study has shown that giant mC can be expected in ferroelectric Ba 0.5 Sr 0.5 TiO 3 10 and BaTiO 3 11. However, there are few experimental reports on caloric effects driven by multi-fields up to now12. In this paper, we report the caloric effect driven by both electric field and strain in antiferroelectric PZT films on 0.7Pb(Mg 1/3 Nb 2/3 )O 3 -0.3PbTiO 3 (PMN-PT) substrate.…”

Present and future caloric refrigeration and heat-pump technologies

“…This is referred to as the multicaloric effect or multicaloric materials or sometimes also multiferroic materials (see e.g., Meng et al (2013), Starkov and Starkov (2014a), Moya et al (2014), , and Planes et al (2014)). The engineering part, required to bring these materials to efficient working devices still remains to be completed.…”

The induced magnetic and electric fields’ paradox leading to multicaloric effects in multiferroics

“…On the other hand, the induced field dH me is the proposed fictitious field that occurs spontaneously due to the application of the E field. According to Lenz's law, the strength of the induced field dH me is exactly as large as needed to account for the change in magnetization M via the well-known magneto-electric effect due to the application of E. This is also the meaning of the negative sign in (11). Therefore, at constant T and H (or zero applied magnetic field), the change dM should be zero as the effect of the applied E field on M is cancelled out by the occurrence of the induced field.…”

“…This is achieved by replacing dH with: me app dH dH dH   (11) Relation (11) shows that the acting magnetic field on the multiferroic is a combination of the externally applied magnetic field, H app and the induced magneto-electric field, H me , where the minus sign indicates that the induced magneto-electric field is opposed to the applied field as dictated by Newton's 3 rd law, or its extension to magnetic phenomena, Lenz's law. Using (11), relation (7) should then be written as: meterms of E and H field vector components and their relationship to the sample geometry, crystal symmetry and directions of polarization and magnetization. This is particularly important when an antiferromagnetic phase exists in the multiferroic or when the sample geometry displays strong spatial variations.…”

“…Vopson also published, a year later, an extension of the 2012 model [10] In 2014, 2 years after the first publication of the Multicaloric Effect by Vopson, A.S. Starkov and I.A. Starkov published the article "Multicaloric Effect in a Solid: New Aspects" [11]. Despite being 2 years late in predicting this effect, the authors "forgot" to make any reference to previously peer review published papers on this effect, including the original article [9] and the follow up published a year later [10].…”