Study On Magnetic-field-induced Phase Transition And The Related Functional Properties Of Ni(Fe)-Mn Based Shape Memory Alloys

As a new shape memory material,magnetic shape memory alloys show shape memory effect not only under temperature and stress,but also under the magnetic field.As a result,magnetic shape memory alloys are expected to be a novel smart material with applications in the fields of aerospace industry,biological engineering,energy and automation due to their giant magnetic-feld-induced strain,high response frequency,precise control,etc.In this work,through manipulating magnetostructural transition in a series of Ni(Fe)-Mn based magnetic shape memory alloys and applying in-situ synchrotron high-energy X-ray diffraction and neutron diffraction techniques,the magnetic-feld-induced phase transition behavior and the related functional properties are studied.The underlying mechanism for anomalous magnetic behavior at extremely low temperature(4 K,far below martensitic transformation temperature)in the Ni37Co11Mn42.5Sn9 5 alloy is studied by applying in-situ neutron diffraction technique.It is shown that the magnetic-field-induced structural transition occurring at this extremely low temperature is responsible for the anomalous low-temperature magnetic behavior.It is believed that this transition proceeds by a succession of discrete steps,accounting for the abrupt jump on the magnetization curve.The present study provides deep insights into the interplay between magnetism and structure in magnetic shape memory alloys to design new functional properties,and it is also instructive for understanding the anomalous staircase-like magnetization behavior in other materials.The phase transition behavior is systematically studied in a series of ternary Fe43-xMn2gGa29+x(x= 0,0.5,1.0,1.5,1.7,1.9 and 2.0)magnetic shape memory alloys.It is shown that strain glass transition is observed in this alloy system when x exceeds a critical value xc(xc≥2.0).Based on the results,a temperature-composition phase diagram of the Fe43-xMn28Ga29+x alloys is established,which includes the martensite and strain glass in this system.The results show that below the freezing temperature T0,applying external magnetic field can induce a first-order phase transition in the Fe41Mn28Ga31 alloy,which is accompanied by sharp magnetization jumps during increasing the magnetic field.In-situ neutron diffraction is applied to directly disclose that the magnetic-field-induced strain-glass-to-martensite transition is responsible for this specific phase transition behavior.A scenario was proposed to interpret the structure evolution and the M(H)behavior associated with the magnetic-field-induced strain-glass-to-martensite transition.Finally,the potential magnetocaloric effect and shape memory effect of the Fe41Mn28Ga31 strain glass alloy are investigated,and by calculation a large ASm of～8.7 J kg-1 K-1 under the magnetic field of～2.1 T at 80 K is achieved.Therefore,this work provides novel practical and theoretical insight into strain glass,which may further elucidate the coupling of ferroic glass and guide the design of new and giant magnetoresponsive materials.Moreover,giant negative thermal expansion(NTE)has been achieved by careful chemical modification in a series of Fe-Mn-Ga magnetic shape memory alloys.Martensitic transformation from the cubic austenite to the tetragonal martensite,which is accompanied with a large positive volume change,is responsible for the NTE behavior.Through chemical modification,the wide operating temperature windows of large NTE can shift from near room temperature to cryogenic temperature.Typically,the Fe43Mn28Ga29 alloy exhibits a wide NTE temperature window between 290 K and 209 K and a giant NTE coefficient of α1=-50.2 ×10-6 K-1.These alloys show excellent mechanical properties,high electrical conductivity and high thermal conductivity.Consequently,the studied Fe-Mn-Ga alloys have great potential for NTE applications.The magnetostructural transition in the Ni-(Co)-Mn-In magnetic shape memory alloys is manipulated via systematically tuning the Mn/In ratio and the Co substitution in a series of compositions.It is found that an optimum composition Ni49Co3Mn34In14 alloy shows with a low thermal hysteresis of 8 K,a narrow transformation interval of 7 K and a high sensitivity of transformation temperature to field change of 6 K T-1.Good geometric compatibility between austenite and martensite is revealed by in-situ synchrotron high-energy X-ray diffraction experiment.A reversible magnetic-field-induced transformation between pure martensite and pure austenite occurs under a relatively low magnetic field of 3 T in this alloy,which is directly evidenced by our in-situ neutron diffraction experiment.A large reversible magnetocaloric effect with ASm of 1 6.5 J kg-1 K-1,a large reversible magnetostrain of 0.26%and a large reversible magnetoresistance of 60%,under a relatively low magnetic field of 3 T,are simultaneously achieved in this Ni49Co3Mn34In14 alloy.The magnitudes of these reversible magnetoresponsive effects are comparable to those reported under high magnetic fields(above 5 T)in other Ni-Mn-based magnetic shape memory alloys,but the magnetic field required to induce the magnetoresponsive effects in the present work is drastically lower.This study may guide the design of metamagnetic shape memory alloys with low-field-induced magnetoresponsive properties for magnetic refrigeration,magnetic sensing and magnetic recording applications.In summary,the magnetic-field-induced phase transition in a series of Ni(Fe)-Mn based magnetic shape memory alloys and the related functional properties are studied.This work provides novel practical and theoretical insight into phase transition behavior in magnetic shape memory alloys,and may also guide the design of new multifunctional materials.