Evolution of the inverse magnetocaloric effect for random-field to spin-glass crossover in SmCaCoMnO6−SmMnO3 nanocomposite

Abstract

We observe an enhancement of inverse magnetocaloric effect (MCE) in $\mathrm{Sm}\mathrm{Ca}\mathrm{Co}\mathrm{Mn}{\mathrm{O}}_{6}$ (94%) and $\mathrm{Sm}\mathrm{Mn}{\mathrm{O}}_{3}$ (6%) nanocomposite due to uniform external field-induced random field (RF) to spin glass (SG) crossover. RF is generally observed in diluted antiferromagnet and dilute dipole-coupled Ising ferromagnet systems. Under the application of magnetic-field ($H$), such systems may show a crossover from RF to SG at low temperatures ($T$). Here, we report a similar type of crossover but in ferrimagnetic $\mathrm{Sm}\mathrm{Ca}\mathrm{Co}\mathrm{Mn}{\mathrm{O}}_{6}$ and antiferromagnetic $\mathrm{Sm}\mathrm{Mn}{\mathrm{O}}_{3}$ nanocomposite. A model of site dilution of the ferrimagnetic phase by the embedded antiferromagnetic regions is proposed. In this composite system, the RF appears at $T<35$ K, which shows a crossover to SG at $T<15$ K under the applied field. The enhanced inverse MCE (with an entropy change, $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}\ensuremath{\sim}\ensuremath{-}0.95$ J ${\mathrm{Kg}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ for a change in $H\ensuremath{\sim}70$ kOe at $T\ensuremath{\sim}7.5$ K) due to the SG state is the consequence of field-induced RF-SG crossover giving highly $H$-dependent $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}$ in the SG regime, a requisite for large MCE.