Vol.:(0123456789) 1 3 Applied Physics A (2020) 126:472 https://doi.org/10.1007/s00339-020-03651-x Effect of Si substitution on the Structural, Magnetic and Magnetocaloric Properties of Ni–Mn–In Heusler alloys N. Pavan Kumar 1,2  · Manvir Singh 3  · Vishal Mahey 3  · Suyesh Nautiyal 3  · D. M. Raj Kumar 1  · N. V. Rama Rao 1  · M. Manivel Raja 1 Received: 27 February 2020 / Accepted: 18 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract The effect of partial substitution of manganese by silicon in Ni 47 Mn 40−x Si x In 13 (x = 1, 2, 3) on the structural (martensitic), magnetic transitions and associated magnetocaloric properties around the martensitic transition of these alloys, was inves- tigated. The alloys exhibited the single austenite structure at the room temperature. The lattice contraction was observed with an increase in Si content, thereby inducing the FM and AFM interactions between manganese atoms, which further influence the magnetic and martensitic transitions. The increase in Si concentration was observed with the decrease in valence electron to atom ratio (e/a ratio) and thus influencing the martensitic transitions. The transition temperatures such as martensitic transition (T M ) and the Curie transition (T C ) of the austenite phase decrease with increasing Si-content. With the increase in Si content from x = 1 to 3, the T M was found to decrease from 259 to 169 K. A high magnetic entropy change (∆S) M of 12.3, 3.1 and 30.6 J kg −1  K −1 was observed for the x = 1, 2, and 3 alloys at their respective martensitic transitions for a magnetic field of 2 T. Keywords Magnetocaloric effect · Heusler alloy · Martensitic transition 1 Introduction The magnetocaloric effect (MCE) is a thermo-magnetic process, where a material heats up or cools down when it is subjected to externally applied changing magnetic field. The phenomenon was first discovered in 1881 by Warburg in iron [1]. There are some materials that show a very high value of MCE near room temperature. Such materials are being studied vastly for their applications in magnetic refrigeration technology as these refrigerants have essential advantages like they are environment friendly and consume less energy when compared to conventional refrigeration technology of gas compression [2–4]. Magnetocaloric effect is usually calculated by isothermal entropy change (∆S), adiabatic temperature change (∆T), and refrigeration capacity (RC), when an external magnetic field is applied on the material. If ∆S is less than 0, the sample gets heated up under the effect of an external field and it is called direct MCE. Similarly, if ∆S is greater than 0, the sample gets cooled down by the applied external field, and the phenomena is called as inverse magnetocaloric effect [5]. If we wish to commer- cially exploit this solid-state refrigeration technology, we require materials showing large MCE parameters like ∆S , (∆T), and refrigerant capacity at the temperature close to the room temperature and that too for quite low values of the applied magnetic field (∆H). Very large MCE was seen in Gd 5 (Si 1−x Ge x ) 4 [6, 7] alloys with ∆S of 19 J K −1  kg −1 when the change in the applied field was of 5-T near the room tem- perature. Until now, various sets of magnetocaloric materials have been probed, including La–Fe–Si [11, 12], MnFe(P, As) [8–10] and Ni–Mn Heusler alloys [13, 14]. Out of these alloys, Ni–Mn alloys which are free from rare earth toxic elements (such as As) are most suited for practical appli- cations. The rare earth elements are expensive because of their relatively short supply. For commercializing solid-state refrigeration technology, it is necessary to synthesize rare earth element free as well as cost-effective MCE materials. * M. Manivel Raja mraja@dmrl.drdo.in 1 Defence Metallurgical Research Laboratory, Hyderabad 500058, India 2 Matrusri Engineering College, Saidabad, Hyderabad 500059, India 3 Department of Materials and Metallurgical Engineering, Punjab Engineering College, Chandigarh 160012, India