Comparison of the dielectric and magnetocaloric properties of bulk and film of GdFe0.5Cr0.5O3

Abstract

Reported here is a comparison of the magnetic, magnetocaloric, and dielectric properties of 50% iron substituted GdCrO3 (GdFe0.5Cr0.5O3) bulk pellet and 960 nm thick film of GdFe0.5Cr0.5O3 (GFCO). The 960 nm film was synthesized on a platinized-silicon substrate by chemical solution deposition and spin-coating methods. The X-ray diffraction scans of the bulk sample and the film as well as the morphology of the film as examined by the field-emission scanning electron microscope indicate phase-pure and polycrystalline nature of these samples. X-ray photoelectron spectroscopy was used to determine the valence states of Gd, Fe, and Cr. The temperature dependence of the dielectric constant from 225 to 700 K shows peaks at TC = 525 K for the bulk and ∼450 K for the film due to ferroelectric to paraelectric transitions, since electric polarization vs electric field hysteresis loops are observed at room temperature. The dielectric studies in the bulk GFCO for T > TC indicate a relaxor-like behavior. The measurements of the magnetization (M) of the samples as a function of temperature (5–350 K) and magnetic field (H) up to 7 T (=70 kOe) depict hysteresis behavior at low temperatures due to the canted antiferromagnetic order of Fe3+/Cr3+ below the Néel temperature of ∼275 K. The M vs H isotherms at various temperatures are used to determine and compare the magnetic entropy change (−ΔS) and relative cooling power (RCP) of the two samples, yielding (−ΔS) = 30.7 J/kg K (18.8 J/kg K) and RCP = 566.5 J/kg (375 J/kg) for the bulk (960 nm film) samples of GFCO at 7 K and 7 T, respectively. The plot of RCP vs T shows that magnetic cooling for this system is most effective for T < 30 K. Comparatively smaller magnitudes of (−ΔS) and RCP for the film vis-à-vis the bulk sample of GFCO scale with its reduced magnetization. This suggests that further improvements in the quality of the films are needed to improve their magnetization and hence their magnetocaloric properties, possibly making them useful for on-chip cooling in miniaturized devices.