Windows open for highly tunable magnetostructural phase transitions

Abstract

An attempt was made to tailor the magnetostructural transitions over a wide temperature range under the principle of isostructural alloying. A series of wide Curie-temperature windows (CTWs) with a maximal width of 377 K between 69 and 446 K were established in the Mn1−yCoyNiGe1−xSix system. Throughout the CTWs, the magnetic-field-induced metamagnetic behavior and giant magnetocaloric effects are obtained. The (Mn,Co)Ni(Ge,Si) system shows great potential as multifunctional phase-transition materials that work in a wide range covering liquid-nitrogen and above water-boiling temperatures. Moreover, general understanding of isostructural alloying and CTWs constructed in (Mn,Co)Ni(Ge,Si) as well as (Mn,Fe)Ni(Ge,Si) is provided.

Large Barocaloric Effect with High Pressure-Driving Efficiency in a Hexagonal MnNi0.77Fe0.23Ge Alloy

“…It seems that the martensitic transition will vanish when the FM transition of parent phase happens first during temperature decreasing. This suppression behavior has been observed in other MM'X compounds [1,9,12] . The interpretation could be that the parent phase is more stable at the FM state than the PM one.…”

“…2 remarkable character, i.e., giant volume expansion with values of 2 ~ 5% during the structural transition upon cooling [1,3,9] . A hydrostatic pressure can drive this transition to lower temperatures as the mechanical energy gain (ΔP·ΔV) in the total Gibbs freedom energy tends to shift the equilibrium point of the phase transition.…”

“…For a hexagonal MM'X family, there is a remarkable character, i.e., giant volume expansion with values of 2-5% during the structural transition upon cooling. [1,3,9] A hydrostatic pressure can drive this transition to lower temperatures as the mechanical energy gain (∆𝑃 •∆𝑉 ) in the total Gibbs freedom energy tends to shift the equilibrium point of the phase transition. Thus, besides the chemical substitution, [10,11] vacancy, [12,13] magnetic field [14] and strain, [15] the hydrostatic pressure is widely used [10,11,16−21] to tune a phase transition.…”

Emergent evolution of first-order phase transitions from magneto-structural to magneto-elastic in MnCo1−y Fe y Ge1−x Si x alloys

“…The increase in T M by introducing Si at sites of the main group elements in a MM ′ X alloy system has been demonstrated in previous literature [13,14,28]. Herein, by taking MnCoSi with T M = 1162 K as its isostructural counterpart, y = 0.2 and y = 0.3 were taken as the basic starting alloys to further tailor the transitions.…”

“…Unfortunately, the magnetic and structural transitions are separated, the MT temperature (T M ) is generally higher than the Curie temperature in martensite (T C M ), and the desired MST with large ∆M cannot be achieved. Subsequently, to couple the structural and magnetic transitions, various methods [11][12][13][14][15][16][17][18] have been used to convert MT to MST and effectively enhance the MCE. Among them, by applying the isostructural alloying principle [11], almost all MSTs can be obtained in the Curie temperature window (CTW) constructed by Curie temperatures in austenite (T C A ) and T C M through precise element substitutions.…”