Giant magnetocaloric effect in Co <sub>2</sub> FeAl Heusler alloy nanoparticles
Aquil Ahmad, Srimanta Mitra, S K Srivastava, A K Das
Abstract
Abstract A giant magnetocaloric effect across the ferromagnetic (FM) to paramagnetic (PM) phase transition was observed in chemically synthesized Co 2 FeAl Heusler alloy nanoparticles with a mean diameter of 16 nm. In our previous report, we observed a significant enhancement in its saturation magnetization ( M s ) and Curie temperature ( T c ) as compared with the bulk counterpart. Motivated by those results, we aim here to explore the magnetocaloric properties near the T c . The magnetic entropy change ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mrow> <mml:msub> <mml:mi>S</mml:mi> <mml:mrow> <mml:mtext>M</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ) shows a positive anomaly at 1252 K. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mrow> <mml:msub> <mml:mi>S</mml:mi> <mml:mrow> <mml:mtext>M</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> increases linearly with the magnetic field, and a large value of ∼15 J kg −1 K −1 is detected under a moderate field of 14 kOe. It leads to a net relative cooling power of 89 J kg −1 for the magnetic field change of 14 kOe. To confirm the nature of magnetic phase transition, a detailed study of its magnetization is performed. The Arrott plot and nature of universal curve conclude that the FM to PM phase transition in the present system is of second-order.