Magnetostructural transformation and magnetocaloric effect in Mn_(48-x)V_(x)Ni_(42)Sn_(10) ferromagnetic shape memory alloys

In this work,we tuned the magnetostructural transformation and the coupled magnetocaloric properties of Mn_(48-x)V_(x)Ni_(42)Sn_(10)(x=0,1,2,and 3)ferromagnetic shape memory alloys prepared by means of partial replacement of Mn by V.It is observed that the martensitic transformation temperatures decrease with the increase of V content.The shift of the transition temperatures to lower temperatures driven by the applied field,the metamagnetic behavior,and the thermal hysteresis indicates the first-order nature for the magnetostructural transformation.The entropy changes with a magnetic field variation of 0-5 T are 15.2,18.8,and 24.3 J.kg^(-1).K^(-1)for the x=0,1,and 2 samples,respectively.The tunable martensitic transformation temperature,enhanced field driving capacity,and large entropy change suggest that Mn_(48-x)V_(x)Ni_(42)Sn_(10)alloys have a potential for applications in magnetic cooling refrigeration.

Enhanced reversibility of the magnetoelastic transition in(Mn,Fe)2(P,Si)alloys via minimizing the transition-induced elastic strain energy

Magnetocaloric materials undergoing reversible phase transitions are highly desirable for magnetic refrigeration applications.(Mn,Fe)_(2)(P,Si)alloys exhibit a giant magnetocaloric effect accompanied by a magnetoelastic transition,while the noticeable irreversibility causes drastic degradation of the magnetocaloric properties during consecutive cooling cycles.In the present work,we performed a comprehensive study on the magnetoelastic transition of the(Mn,Fe)_(2)(P,Si)alloys by high-resolution transmission electron microscopy,in situ field-and temperature-dependent neutron powder diffraction as well as density functional theory calculations(DFT).We found a generalized relationship between the thermal hysteresis and the transition-induced elastic strain energy for the(Mn,Fe)_(2)(P,Si)family.The thermal hysteresis was greatly reduced from 11 to 1 K by a mere 4 at.%substitution of Fe by Mo in the Mn_(1.15)Fe_(0.80)P_(0.45)Si_(0.55)alloy.This reduction is found to be due to a strong reduction in the transition-induced elastic strain energy.The significantly enhanced reversibility of the magnetoelastic transition leads to a remarkable improvement of the reversible magnetocaloric properties,compared to the parent alloy.Based on the DFT calculations and the neutron diffraction experiments,we also elucidated the underlying mechanism of the tunable transition temperature for the(Mn,Fe)_(2)(P,Si)family,which can essentially be attributed to the strong competition between the covalent bonding and the ferromagnetic exchange coupling.The present work provides not only a new strategy to improve the reversibility of a first-order magnetic transition but also essential insight into the electron-spin-lattice coupling in giant magnetocaloric materials.

Large,low-field and reversible magnetostrictive effect in MnCoSi-based metamagnet at room temperature

TiNiSi-type MnCoSi-based alloys show large magnetostriction during the magnetic-field-induced metamagnetic transition.However,the high critical field required to drive the transition directly hinders their potential applications.In this work,we systematically investigate the tricritical behavior and magnetostrictive effect in substituted MnCoSi alloys.Replacing Si with Sb or In,Co with Fe or Cu,and Mn with Co,which can simultaneously reduce the critical field and the temperature of tricritical point,are explored.Among the substituted MnCoSi alloys,Mn_(0.983)Co_(1.017)Si displays a temperature of a tricritical point of 250 K and a room-temperature critical field of 0.60 T,which is the lowest up to now.Profited from these optimizations,a large reversible magnetostrictive effect under low field is successfully realized at room temperature.In a field of 1 T,the magnetostriction of Mn_(0.983)Co_(1.017)Si alloy is close to 1000 ppm.Besides,a strong relation between critical field and valence electron concentration is revealed in the transition-metal-substituted MnCoSi alloys.Our work greatly enhances the low-field magnetostrictive performance of MnCoSi-based alloys and make them be of interest in potential applications.