Opening the Hysteresis Loop in MAB Magnets: Experimental and Computational Studies of CrMn4SiB2 and Mo0.8Mn4.2SiB2

Abstract

This study presents the synthesis and magnetic characterization of two quaternary MAB phases: CrMn₄SiB₂ and Mo_0.8Mn_4.2SiB₂. Using a refined synthesis method, we successfully produced single-phase compounds, overcoming previous challenges associated with impurity phases. Both compounds crystallize in the tetragonal space group I4/mcm, with Mo demonstrating distinct site preferences in Mo_0.8Mn_4.2SiB₂. Magnetic measurements indicate the presence of long-range ferromagnetic interactions, with Curie temperatures (T_C) of approximately 270 K for CrMn₄SiB₂ and 340 K for Mo_0.8Mn_4.2SiB₂. Field-dependent magnetization measurements indicate a saturation magnetization (M_s) of 5.128 μ_B/f.u. (at 5 K) for CrMn₄SiB₂ and 6.214 μ_B/f.u. (at 5 K) and 3.692 μ_B/f.u. (at 300 K) for Mo_0.8Mn_4.2SiB₂. The introduction of Mo or Cr in the ternary parent compound Mn₅SiB₂, opens a hysteresis for the first time in this class of T2 phases, with intrinsic coercivities of H_c = 5.57 kA/m for CrMn₄SiB₂ and 6.53 kA/m for Mo_0.8Mn_4.2SiB₂. Density functional theory (DFT) calculations confirm the ferromagnetic ordering while the magnetocrystalline anisotropy energy (MAE) calculations show that CrMn₄SiB₂ and MoMn₄SiB₂ have in-plane anisotropy with higher MAE values than Mn₅SiB₂, thus confirming experimental findings. This research not only introduces a synthesis pathway toward single-phase T2-based quaternary materials, but it also opens an avenue toward MAB-based permanent magnets.