Influence of negative lattice expansion and metamagnetic transition on magnetic entropy change in the compound LaFe11.4Si1.6

TLDR

The authors measured temperature‑ and field‑dependent magnetization of LaFe11.4Si1.6 near its 208 K Curie point and derived the magnetic entropy change using the Maxwell relation, noting a fully reversible transition. The compound exhibits a large reversible magnetic entropy change of 19.4 J kg⁻¹ K⁻¹ at 5 T, attributed to a sharp magnetization drop driven by negative lattice expansion at TC, and shows an asymmetrically broadened ΔS peak with field due to a field‑induced itinerant‑electron metamagnetic transition above TC.

Abstract

Magnetization of the compound LaFe11.4Si1.6 with the cubic NaZn13-type structure was measured as functions of temperature and magnetic field around its Curie temperature TC of ∼208 K. It is found that the magnetic phase transition at TC is completely reversible. Magnetic entropy change ΔS, allowing one to estimate the magnetocaloric effect, was determined based on the thermodynamic Maxwell relation. The achieved magnitude of |ΔS| reaches 19.4 J/kg K under a field of 5 T, which exceeds that of most other materials involving a reversible magnetic transition in the corresponding temperature range. The large entropy change is ascribed to the sharp change of magnetization, which is caused by a large negative lattice expansion at the TC. An asymmetrical broadening of |ΔS| peak with increasing field was observed, which is resulted from the field-induced itinerant-electron metamagnetic transition from the paramagnetic to ferromagnetic state above the TC.