Page 61 - Annual Report_21-22

Giant magnetocaloric effect in rare earth based oxides and applications thereof
Conventional gas refrigeration technology possesses shows a giant isothermal magnetic entropy change (ΔS )
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several drawbacks in power consumption and greenhouse as compared to GdMnO , but with similar relative cooling
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gas emissions. Taking into account these issues, alternate power (RCP). However, the absence of magnetic and
solutions for cooling applications, especially for cryogenic thermal hysteresis in GdAlO makes it a more efficient
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temperatures, are being explored. Magnetic refrigeration magnetic refrigerant than GdMnO . DyMnO shows
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(MR) technology that works on the magnetocaloric moderate magnetocaloric effect, but it could be enhanced
effect principle is one such alternative. Rare-earth based with Gd- doping suggesting that rare earth mixing plays
oxides are predicted to be suitable candidates for low- a vital role in modifying the magnetocaloric properties.
temperature magnetic cooling due to their low magnetic GdCrO and GdCr Fe O show exceptionally high values
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ordering temperature in the rare-earth sub-lattices, large for ΔS , ΔT and RCP (41 Jkg K , 20.8 K and 560 Jkg ,
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magnetization, weak magnetic exchange interactions, respectively, for a field change of 7 T and 44.9 Jkg K ,
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negligible thermal and field hysteresis. The phenomena of 15.1 K and 691.8Jkg , respectively, for a field change of
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magnetocaloric effect in various rare-earth oxides of type 9 T) making them best candidates for MR at cryogenic
AA’BO where A, A’ = Gd, Dy and B = Cr, Mn, Fe and Al and temperatures. We are currently working on higher
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their structural, electronic, magnetic and magnetocaloric order perovskite systems as well for enhancing their
properties are being extensively investigated. GdAlO magnetocaloric responses.
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Figure: X-ray diffraction pattern of GdCr Fe O system along with the Rietveld refinements for extracting the crystal
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structure parameters. Raman spectroscopy spectra as well as SEM images showing the morpology are also presented. (c)
X-ray photoemission spectra of GdCr Fe O system showing the Gd 3d core levels and isothermal magnetization curves
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between temperature range of 2 K to 30 K for varying magnetic fields are also presented.
ANNUAL REPORT 2021-22 59