Pressure-induced giant enhancement of magnetocaloric effects in MnNiSi-based systems

TL;DR

Applying low hydrostatic pressure to MnNiSi-based systems significantly amplifies their magnetocaloric effect near room temperature, enabling efficient magnetic cooling with minimal hysteresis losses.

Contribution

This study demonstrates that pressure can dramatically enhance the magnetocaloric effect in MnNiSi-based systems by coupling magnetic and structural transitions, a novel approach for magnetic refrigeration.

Findings

Pressure increases entropy change from 44 to 89 J/kg K at 5 T.

Giant volume change (~7%) occurs during transition under pressure.

Transition temperature can be tuned with pressure, reducing hysteresis.

Abstract

A remarkable decrease of the structural transition temperature of MnNiSi from 1200 K to <300 K by chemically alloying it with MnFeGe results in a coupling of the magnetic and structural transitions, leading to a large magnetocaloric effect near room temperature. It was found that the magnetostructural transition is highly sensitive to external (hydrostatic) pressure: relatively low hydrostatic pressures (~2.4 kbar) lead to an extraordinary enhancement of the isothermal entropy change from $-$\Delta $S$ = 44 to 89 J/kg K at ambient (atmospheric) and 2.4 kbar applied pressures, respectively, for a field change of \Delta $H$ = 5 T. This giant entropy change is associated with a large relative volume change of about 7% induced by 2.4 kbar applied pressure during the magnetostructural transition. The pressure-enhanced magnetocaloric effects are accompanied by a shift in transition temperature, an effect that may be exploited to tune the transition to the required working temperature, and thereby eliminate the need for a given material to possess a large magnetocaloric effect (i.e., entropy change) over a wide temperature range. Furthermore, this material also possesses negligible hysteresis losses.