Magnetocaloric materials are researched as promising alternatives to conventional gas compression technologies for heat conversion. Within the known magnetocaloric materials, the MM'X system is promising as it features a strong first order magnetostructural transition (MST) enabled by partial substitution of M, M' and X sites, where M and M' are transition metals and X is a p-block element in orthorhombic/hexagonal structures1. Commonly used intermetallics (MnNiGe, MnCoGe 2,3) employ Ge and Co, which are critical for their applications in electronics, and cathode materials for batteries, respectively. In the present study, Fe and Al substitutions inside a MnNiSi-based intermetallic induce a MST without critical or expensive elements. All alloys have been synthesized by arc melting, and heat treated followed by quenching. By convenient substitution, the studied Mn1-xNi1-xFe2xSi0.95Al0.05 alloys exhibit Curie temperatures around room-temperature, which were captured by Vibrating Sample Magnetometry (VSM) as well as In-field differential scanning calorimetry (DSC) 4. The VSM magnetization over temperature data in the Mn0.69Ni0.69Fe0.62Si0.95Al0.05 sample with applied field μ0H = 1 T shown in Fig. 1 displays an abrupt variation of magnetization with temperature, where the derivatives of magnetization exhibit a minimum between 279 and 290 K during cooling and heating, respectively. From the VSM measurements, what can be thought of as a single-phase transition due to a single derivative minimum can be elucidated with the use of a 1K/min heating/cooling rate in the DSC. In fact, this MST is a convolution of different transitions all close to one another, as shown during the cooling protocol in Fig. 2 from in-field DSC data with 1 T applied field. The main article will investigate the cause of such distribution of transitions and its effect on the isothermal entropy change during heating and cooling transformations, as evaluated by a concurrent VSM and DSC study.

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1 W. Bazela, A. Szytula, J. Todorovic, A. Zieba, Crystal and magnetic structure of the NiMnGe1−nSin System, Phys. Status Solidi. 64 (1981) 367–378. https://doi.org/10.1002/pssa.2210640140.
2 A. Taubel, T. Gottschall, M. Fries, T. Faske, K.P. Skokov, O. Gutfleisch, Influence of magnetic field, chemical pressure and hydrostatic pressure on the structural and magnetocaloric properties of the Mn-Ni-Ge system, J. Phys. D. Appl. Phys. 50 (2017). https://doi.org/10.1088/1361-6463/aa8e89.
3 S.K. Pal, C. Frommen, S. Kumar, B.C. Hauback, H. Fjellvåg, G. Helgesen, Enhancing giant magnetocaloric effect near room temperature by inducing magnetostructural coupling in Cu-doped MnCoGe, Mater. Des. 195 (2020) 109036. https://doi.org/10.1016/j.matdes.2020.109036.
4 K.K. Nielsen, H.N. Bez, L. Von Moos, R. Bjørk, D. Eriksen, C.R.H. Bahl, Direct measurements of the magnetic entropy change, Rev. Sci. Instrum. 86 (2015). https://doi.org/10.1063/1.4932308.