Structural evolution and tunable magnetic response in novel TiZrVCrNiFe-X (X = Mn, MnCo) alloys: An experimental and thermodynamic study

Abstract

In this study, chemically complex TiZrVCrNiFe-X alloys with X = Mn and MnCo were examined to determine how B-sublattice chemistry influences the stability of the C14 Laves phase during heating and the resulting magnetic response. Room-temperature X-ray diffraction and backscattered scanning electron microscopy show a dominant C14 (MgZn<inf>2</inf>, P6<inf>3</inf>//mmc) matrix in both alloys, together with a minor V- and Cr-rich segregation at the few-percent level, consistent with solidification-related microsegregation. Co addition produces a measurable contraction of the C14 lattice, strongest along the c axis. Differential scanning calorimetry shows a shallow endothermic feature near 773–797 °C, indicating the onset of diffusion-assisted chemical rearrangement. In-situ high-temperature X-ray diffraction confirms that the C14 lattice remains intact through the intermediate-temperature regime up to 700 °C, followed by the gradual appearance of a BCC-type secondary phase in both alloys and additional σ-phase reflections only in the Co-bearing alloy, while C14 reflections persist throughout. Together with post-annealing scanning electron microscopy/energy dispersive spectroscopy at 800 °C, this establishes diffusion-limited precipitation from a C14 matrix rather than a reconstructive C14→BCC transformation. The temperature evolution of a(T) and c(T) is weak in the C14-dominant regime and shows earlier deviations in the Co alloy, consistent with increased misfit and partitioning as secondary products develop. Magnetometry from 10 to 300 K indicates Curie-Weiss paramagnetism for both compositions with Curie-Weiss temperatures close to zero and large effective moments arising from multiple 3d species. Co addition markedly increases the low-temperature magnetization, consistent with the intrinsic Co 3d moment and its effect on the local 3d environment within the C14 matrix. Overall, Mn↔Co substitution provides a practical route to tune the chemical stability of a C14 Laves backbone against BCC-type and σ precipitation on heating while independently adjusting the magnetic response. © 2026 Elsevier B.V.