Employing the principle of isostructural alloying, a series of unprecedentedly wide Curie-temperature windows (CTWs), covering the ultimate temperature range of first-order magnetostructural phase transitions (MSTs), are realized between 40 and 450 K for the strongly-coupled MSTs in a single host system Mn 1-y Fe y NiGe 1-x Si x . Throughout the wide CTWs, the highly tunable MSTs show large magnetization jump, low-field effects, high-temperature giant magnetocaloric effects and robust functional stability, providing important properties to phase-transition-based magneto-multifunctional applications, including field-driven shape memory, magnetic cooling/heating and energy conversion. The unprecedentedly wide CTWs open up a design platform for magneto-multifunctional multiferroic alloys that can be manipulated in a quite large temperature space in various scales and patterns, and by multiple physical fields.
Keywords:Curie-temperature window, magnetic shape memory alloy, magnetocaloric effect, ferromagnetic martensitic transition, magnetostructural transition 3 A coupling of ferroelasticity and ferromagnetism [1, 2] can lead to a multiferroic behavior of first-order magnetostructural phase transition (MST) in magnetoelastic materials.Attractive physical effects, such as ferromagnetic shape memory, [3] magneto-strain, [4] magnetocaloric effect (MCE), [5, 6] magnetoresistance, [7] and exchange bias, [8] are observed based on the MSTs. These effects are receiving increasing attentions from the applications in actuating, [9] sensing, [10] magnetic cooling, [11] heat pump [12] and energy conversion. [13] As an important class of MSTs, ferromagnetic martensitic transformations (FMMTs) are widely found in Heusler, Fe-based, and MM'X alloys, and produce diversiform physical discontinuities due to the significant alterations in crystallographic, electronic, orbital and magnetic structures in the systems. Extraordinary magneto-multifunctional properties emerge thereby and can be tuned in different ways.Profiting from FMMTs, the magnetic-field-induced shape memory effect and giant magneto-strain/magnetostriction have been extensively studied with promising potential in micro-mechanical controls and strain outputs. The magnetocaloric effect (MCE), [14] which happens in a magnetic transition, can be enhanced appreciably by first-order FMMTs with great changes in structural entropy in spin-lattice coupled systems. [15][16][17]
Materials bearingFMMTs are thus further considered as candidates for caloric applications, probably combined with mechanocaloric or electrocaloric effects. [18, 19] Very recently, an inspiring application of electric power generation, [20, 21] using first-order FMMT ferromagnets driven by high-temperature heat resources, becomes increasingly attractive for the energy conversion, which demonstrates an exciting advance in magneto-multifunctionalities of magnetoelastic alloys. 4 For all the magneto-multifunctionalities, the magnetostructural coupling play...