Unprecedentedly Wide Curie‐Temperature Windows as Phase‐Transition Design Platform for Tunable Magneto‐Multifunctional Materials

Abstract

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...

Windows open for highly tunable magnetostructural phase transitions

“…With increasing Co content ( y), at the same time the T C A (also lower critical temperature, T cr ) of CTW decreases from 125 K to 69 K. These behaviors are consistent with those in Mn 1−y Fe y NiGe 1−x Si x system. 28 This brings about an encouraging result that the width of the CTW between upper and lower T cr s is increased from 230 K to 377 K. The broad and extended CTW series are realized in Mn 1−y Co y NiGe 1−x Si x system. According to our previous study, 21 high Co content can highly stabilize the parent phase of Mn 1−y Co y NiGe since the isostructural counterpart CoNiGe has a stable parent structure, as shown in Fig.…”

“…This situation is also applicable to Mn 1−y Fe y NiGe, 14 25,28,32 which narrows the CTWs and constrains the MSTs at high temperature range. Nowadays, almost all the MSTs of MM ′ X compounds are studied within the CTWs, in order to get large magnetization changes and desired properties.…”

“…During the composition design, it is necessary to pay more attention to this difference of atom occupying sites and the atom-resolved magnetic exchange interactions, which is an important base for accurate applications of the so-called isostructural alloying principle. 14,21,28 Confusion of site difference and negligence of CTW will lead to inefficient results or even wrong conclusions, like the case in Ref. 36 can be attributed to the slight influence of the main-group elements in Ni-(Ge,Si) covalent networks on magnetic moments of metallic Mn/Co atoms.…”

“…1(a)) and 12.4% for Mn 1−y Fe y NiGe 1−x Si x . 28 The large ∆V/V may enhance the MCEs that originated from magnetic and structural entropy changes. 41 At the same time, these large ∆V/V and uniaxial strain may bring considerable mechanocaloric effects (mCEs) including barocaloric and elastocaloric effects.…”

“…14,21 By further applying isostructural alloying to Mn 1−y Fe y NiGe and MnNiSi, an unprecedentedly wide CTW of 400 K has been achieved. 28 According to the principle of isostructural alloying, a proper isostructural counterpart with a MT and a T C M both at high temperatures should be selected to tune MSTs of Mn 1−y Fe y NiGe to high temperatures. 14,21 This is why MnNiSi was chosen, whose MT temperature (T t ) and T C M are as high as 1200 K and 622 K, respectively.…”