Drastic Influence of Synthesis Conditions on Structural, Magnetic, and Magnetocaloric Properties of Mn(Fe,Ni)(Si,Al) Compounds

Nuendute, Balnude; Gai, H.; Yibole, Hargen; Tana, Bao; Tegus, Ojiyed; Guillou, Francois

doi:10.3390/cryst12020233

Drastic Influence of Synthesis Conditions on Structural, Magnetic, and Magnetocaloric Properties of Mn(Fe,Ni)(Si,Al) Compounds

Title

Drastic Influence of Synthesis Conditions on Structural, Magnetic, and Magnetocaloric Properties of Mn(Fe,Ni)(Si,Al) Compounds

Author

Nuendute, Balnude (Inner Mongolia Normal University China)
Gai, H. (TU Delft RST/Fundamental Aspects of Materials and Energy)
Yibole, Hargen (Inner Mongolia Normal University China)
Tana, Bao (Inner Mongolia Normal University China)
Tegus, Ojiyed (Inner Mongolia Normal University China)
Guillou, Francois (Inner Mongolia Normal University China)

Date

2022

Abstract

Mn compounds presenting magneto-structural phase transitions are currently intensively studied for their giant magnetocaloric effect; nevertheless, several parameters remain to be further optimized. Here, we explore the Mn(Fe,Ni)(Si,Al) series, which presents two advantages. The Mn content is fixed to unity ensuring a large saturation magnetization, and it is based on non-critical Si and Al elements instead of the more commonly employed Ge. Structural and magnetic properties of MnFe_0.6 Ni_0.4 Si_1-x Al_x compounds are investigated using powder X-ray diffraction, SEM, EDX, DSC, and magnetic measurements. We demonstrate that a magneto-structural coupling leading to transformation from ferromagnetic with orthorhombic TiNiSi-type structure to a paramagnetic hexagonal Ni₂ In-type phase can be realized for 0.06 < x ≤ 0.08. Unfortunately, the first-order transition is relatively broad and incomplete, likely as the result of insufficient sample homogeneity. A comparison between samples synthesized in different conditions (as-cast, quenched from 900^◦ C, or quenched from 1100^◦ C) reveals that Mn(Fe,Ni)(Si,Al) samples decompose into a Mn₅ Si₃-type phase at intermediate temperatures, preventing the synthesis of high-quality samples by conventional methods such as arc-melting followed by solid-state reaction. By identifying promising MnFe_0.6 Ni_0.4 Si_1-x Al_x compositions, this study paves the way toward the realization of a giant magnetocaloric effect in these compounds using alternative synthesis techniques.