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Applicant:
Indian Institute of Technology (IIT) Patna 
Author:
P Sivaprakash, S Esakki Muthu, Anupam K Singh, KK Dubey, M Kannan, S Muthukumaran, S. Guha, M. Kar, S. Singh, S Arumugam 
Corresponding Authors:
S Arumugam 
DOI #:
https://doi.org/10.1016/j.jmmm.2020.167136 
Title:
Effect of chemical and external hydrostatic pressure on magnetic and magnetocaloric properties of Pt doped Ni2MnGa shape memory Heusler alloys 
Journal:
Journal of Magnetism and Magnetic Materials 
Year:
2020 
Volume:
514 
Page:
167136 
Keywords:
Magnetocaloric effect, Heusler alloys, Martensite transition, Shape Memory alloys, Hydrostatic pressure 
Abstract:
The magnetocaloric effect (MCE) on Ni2−xPtxMnGa (x= 0.2, 0.3 and 1.0) shape memory Heusler alloys aroundmartensite phase transition temperature (TM) is investigated by varying chemical pressure (Pt concentration).The magnetic entropy change (ΔSM) decreases with increasing chemical pressure for various external appliedmagneticfields up to 3 T, and the width of thermal hysteresis increases with the increases of Pt concentration.The effect of hydrostatic pressure on both TMandΔSMfor Ni1.8Pt0.2MnGa is also investigated. We observed thatthe application of hydrostatic pressure increases TM(3.5 K/GPa) and stabilizes the martensite phase. Themaximum magnetic entropy change (ΔSmax) of 9.31 J Kg−1K-1is observed for afield change of 9 T at ambientpressure for Ni1.8Pt0.2MnGa. Further, the application of external pressure leads to the decrease ofΔSmaxto 5.52 JKg−1K−1at 0.91 GPa.1. IntroductionShape memory Heusler alloys (SMHAs) are of current interest due totheir potential applications in magnetic refrigeration[1], magneticactuation[2],and spintronics devices[3],etc. These alloys exhibit bothstructural and magnetic transitions[4–6]. During the structural phasetransition, the high temperature austenite phase, which has cubiccrystal structure, transforms to the low temperature martensite phasewhich has lower symmetry structure[7]. A good control of magneticphase transition and magnetic property of Ni-Mn-X (X = In, Ga, Sn)SMHA’s show multifunctional properties[8–10]. Among SMHAs, thenovel properties of Ni-Mn-Ga alloys received huge attention due to itslarge magneticfield induced strain (MFIS) owing to their potentialapplications in sensors and actuators[9,11]. The MFIS of 10% has beenobserved in Ni2MnGa ferromagnetic shape memory alloy (FSMA) whichis believed to be related with its modulated orthorhombic structure ofthe martensite phase[12,13].The martensite phase transformationexhibits in these alloys not only to provide large MFIS but responsiblefor other multifunctional properties such as the shape memory effect(SME)[2],magneto-resistance (MR)[14,15], magneto caloric effect(MCE)[16,17]and exchange bias phenomenon[18,19]etc. From theabove mentioned properties, MCE shows the potential application insolid-state cooling technology[4,5]. Recently Pt doped Ni2MnGa havecreated a lot of attention due to their higher transition temperatures,and both theoretical and experimental studies indicate that these alloysmay exhibit better magnetic and mechanical properties[6,18,20–22].In general, in Ni-Mn-X (X = In, Ga, Sn) SMHAs, the structure, and theirmagnetic properties are very sensitive to their chemical composition[23]. Apart from the chemical composition, external parameters such asthe magneticfield and pressure are expected to strongly influence theirstructure and magnetic properties[24,25]The hydrostatic pressures areknown to play a significant role in the structure and magnetic proper-ties of these systems[24,26–28]. The relative stability of the hightemperature cubic austenite phase and the low temperature martensitephase could be influenced by pressure[15,29]. For the composition ofNi-Mn-Ga FSMAs, the exchange interaction of Mn-Mn is strongly de-pendent on the Mn-Mn distance which can be easily altered by eitherhydrostatic pressure or chemical substitutions[9,10].https://doi.org/10.1016/j.jmmm.2020.167136Received 1 April 2020; Received in revised form 8 May 2020; Accepted 10 June 2020⁎Corresponding author.E-mail address:sarumugam1963@yahoo.com(S. Arumugam).Journal of Magnetism and Magnetic Materials 514 (2020) 167136Available online 12 June 20200304-8853/ © 2020 Elsevier B.V. All rights reserved.T  
Entered by:
Venkata Dantham on 2020-08-02 
 
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