Mn₅Si₃ Nanoparticles: Synthesis and Size-Induced Ferromagnetism

Mn-based silicides are fascinating due to their exotic spin textures and unique crystal structures, but the low magnetic ordering temperatures and/or small magnetic moments of bulk alloys are major impediments to their use in practical applications. In sharp contrast to bulk Mn₅Si₃, which is paramagnetic at room temperature and exhibits low-temperature antiferromagnetic ordering, we show ferromagnetic ordering in Mn₅Si₃ nanoparticles with a high Curie temperature (T_c ≈ 590 K). The Mn₅Si₃ nanoparticles have an average size of 8.6 nm and also exhibit large saturation magnetic polarizations (J_s = 10.1 kG at 300 K and 12.4 kG at 3 K) and appreciable magnetocrystalline anisotropy constants (K₁ = 6.2 Mergs/cm³ at 300 K and at 12.8 Mergs/cm³ at 3 K). The drastic change of the magnetic ordering and properties in the nanoparticles are attributed to low-dimensional and quantum-confinement effects, evident from first-principle density-functional-theory calculations.