Enhanced magnetocaloric effect in aluminum doped Gd3Fe5-xAlxO12 garnet: Structural, magnetic, and Mössbauer study


We report a detailed structural, magnetic, and magnetocaloric study on the Aluminum substituted Gadolinium iron garnet. Gd3Fe5-xAlxO12 nanocrystalline powders prepared by auto combustion method followed by sintering at 1100 °C were all single-phase with cubic Ia3¯d symmetry. The lattice parameter and cell volume decreased upon Al3+ substitution. The X-ray diffraction, temperature, and field-dependent magnetization data, Mössbauer spectroscopy complemented with first-principles density functional calculation (DFT) provided evidence of Al3+ substitution at the tetrahedral site for x ≤ 0.5 and partial substitution at both tetrahedral and octahedral sites for x = 1 sample. With the substitution of Al3+ at the spin-down tetrahedral Fe3+ site, the saturation magnetization increased. The Gd3Fe5-xAlxO12 samples presented ferrimagnetic ordering at low temperatures. The maximum magnetic entropy change, derived from magnetic isotherms in field up to 3T, in Gd3Fe5-xAlxO12, was observed to vary from ∼1.94 to ∼3.07 J kg−1 K−1 for x = 0.0 and x = 1.0, respectively. While the maximum relative cooling power value of 226 J kg−1 was measured for x = 0.25 sample. The magnetocaloric peak's genesis is linked to the Gd sublattice's enhanced magnetism and ferromagnetic ordering at low temperatures.

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