Design And Study Of High-working Temperature Ni-Mn-In Magnetic Memory Alloys

Ni-Mn-In magnetic shape memory alloy has an excellent magnetic shape memory effect,magnetocaloric effect and elastocaloric effect,etc.It has a broad development prospect in aerospace,smart materials and medical fields.However,its low working temperature severely limits its application in a high-temperature environment,so it is necessary to develop Ni-Mn-In alloys with high working temperatures.To solve the above problems,this paper adopts three methods to increase the working temperature of Ni-Mn-In alloy based on the first-principle calculation:Pt element doping,vacancy regulation and hydrostatic pressure/biaxial strain regulation,respectively.We improve the working temperature and mechanical properties of Ni-Mn-In alloys by Pt element doping.The calculations show that Pt occupying Ni sites can increase the martensitic transformation temperature（T_M）and curie temperature（T_C）simultaneously.The T_M and T_Cof Ni₁₄Mn₁₂In₄Pt₂ are predicted to be as high as 400K and 476 K,respectively.This is mainly due to the increased phase stability of the martensite and Pt-Mn bonds having stronger ferromagnetic exchange effects than Ni-Mn bonds after Pt doping.Moreover,according to the increase of B/G andυafter Pt doping,it can be concluded that the mechanical properties of the alloy have been improved.We have significantly increased the working temperature of Ni-Mn-In-Co alloy by vacancy defects.We systematically investigated the effect of three vacancy defects,In vacancy,Ni vacancy and Mn vacancy,on the working temperature of Ni-Mn-In-Co alloy,where In vacancy significantly increased the alloy T_M,and Ni vacancy and Mn vacancy both decreased the alloy T_M;all three vacancy modulations had little effect on the alloy T_C.In addition,In vacancies slightly increase the magnetization intensity difference between austenite and 6M martensite phases(ΔM_A-6M)and between austenite and NM martensite phases(ΔM_A-NM).The working temperature of Ni-Mn-In-Co alloy is dynamically adjusted by hydrostatic pressure and biaxial strain.Our results show that Ni₂₁Mn₁₈In₆Co₃presents an adjustable operating temperature range（from 372 K to 393 K）under pressure（0-3 GPa）.Unlike hydrostatic pressure,biaxial stress with compression or tension can achieve bidirectional control of martensitic transformation temperature,further widening the operating temperature range.The biaxial strain from-1.5%to1.5%can tune the operating temperature range from 360 K to 420 K in Ni₂₁Mn₁₈In₆Co₃ alloys.Also,the physical mechanism of dynamic control and increase of working temperature range in Ni-Mn-In-Co using physical pressures is revealed in detail.Moreover,the results show that both hydrostatic pressure and biaxial stress do not decrease the curie temperature（T_C）,and improve theΔM_A-NM.It further proves that applying physical pressures can be an effective strategy with simultaneous enhancement of working temperatures and magnetic properties.