Effects of heat treatments on magneto-structural phase transitions in MnNiSi-FeCoGe alloys. (September 2019)

• Record Type: Journal Article
• Authors: Chen, Jing-Han; Poudel Chhetri, Tej; Us Saleheen, Ahmad; Young, David P.; Dubenko, Igor; Ali, Naushad; Stadler, Shane
• Is Part Of: Intermetallics. Volume 112(2019:Sep.)
• Publication Date: 2019-09
• Subjects: Intermetallic compounds -- Metallography -- Periodicals; Metallic glasses -- Periodicals; Composés intermétalliques -- Métallographie -- Périodiques; 669.94
• DOI: 10.1016/j.intermet.2019.106547
• Languages: English
• ISSNs: 0966-9795

Abstract

Abstract: A first-order magneto-structural transition from a ferromagnetic orthorhombic TiNiSi-type martensite phase to a paramagnetic hexagonal Ni2 In-type austenite phase was observed in (MnNiSi)0.62 (FeCoGe)0.38 . In this work, we demonstrate that the first-order magneto-structural transition temperature for a given composition is tunable over a wide temperature range through heat treatment and hydrostatic pressure application. The first-order transition temperature decreased by over 150 K as the annealing/quenching temperature went from 700 to 1050 ° C . The largest maximum magnetic-field-induced isothermal entropy change with μ 0 Δ H = 7 T reached −36.2 J/kg-K for the sample quenched at 700 ° C, and the largest effective refrigeration capacity reached 344.5 J/kg for the sample quenched at 800 ° C . Similar to the influence of annealing temperatures, the first-order martensitic transition temperatures decreased as the applied hydrostatic pressure increased until they were completely converted to second order. Our results suggest that the class of MnNiSi-based alloys is a promising platform for tailoring working temperature ranges and associated magnetocaloric effects through heat treatment or application of hydrostatic pressure. Highlights: First-order transition are tunable for a wide temperature range by heat treatments. Direct evidence of structural transitions from Ni2 In-type hex. to TiNiSi-type ortho. Magnetic and structural changes are coupled across martensitic transitions.