Alok Shankar | Searcharxiv

arXiv2015

Effects of pressure on the magnetostructural and magnetocaloric properties of isostructurally alloyed (MnNiSi)1-x(FeCoGe)x

The isostructural alloying of two compounds with extremely different magnetic and thermo-structural properties has resulted in a new system, (MnNiSi)1-x(FeCoGe)x, that exhibits extraordinary magnetocaloric properties with an acute sensitivity to applied hydrostatic pressure (P). Application of hydrostatic pressure shifts the first-order phase transition to lower temperature ($Δ$ T=-41 K with P=3.43 kbar) but preserves the giant value of isothermal entropy change (-$Δ$S$\max$=143.7 J/kg K for a field change of ΔB=5 T at atmospheric pressure). Together with the magnetic field, this pressure-induced temperature shift can be used to significantly increase the effective relative cooling power.

cond-mat.mtrl-sci↗

arXiv2014

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

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 $-$Δ$S$ = 44 to 89 J/kg K at ambient (atmospheric) and 2.4 kbar applied pressures, respectively, for a field change of Δ$H$ = 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.

cond-mat.mtrl-sci↗