Study of Stability and Thermo-magnetic Response of MnCoFeGeSi Mechanically Alloyed Systems

Abstract

Amorphous precursors with the composition MnCo0.8Fe0.2Ge1-xSix, where x = 0.2, 0.3, 0.4, and 0.6, were obtained through mechanical alloying. These precursors were subsequently subjected to different thermal treatments, resulting in the formation of the austenite Ni2In-type structure for x ≤ 0.4. For the highest Si content (x = 0.6), this phase coexists with the martensite TiNiSi-type structure without apparent partitioning of the elements at the nanoscale. These structures remain stable up to their melting points, but subsequent melting processes exhibit differences compared to the initial solidification at a cooling rate of − 20 K/min. The magnetocaloric effect was investigated through thermomagnetic and heat capacity measurements and simulated using the Arrott-Noakes equation of state, revealing the presence of a distribution of Curie temperatures. Despite the absence of a martensitic transformation, these alloys exhibit a significant magnetocaloric response, which increases as the precursor system's amorphization (i.e., homogenization) is enhanced.