Grafted magnet C-Mn0.5Bi0.5 with a cohesive C-sp2 spin layer and its impacts on the exchange-coupled magnetic properties

The Mn0.5Bi0.5 is a model rare-earth-free alloy of profound properties for uses as small magnets, tools and many other devices. In a view to upgrade its features, here we report that a grafted C-Mn0.5Bi0.5 exhibits superior magnetic properties in small core-shells. It is safer from erosion in air atmosphere. When milling Mn0.5Bi0.5 (a fine powder) with carbon, up to 4 wt%, in hexane (or a similar lubricant) in an autoclave, a grafted C-sp2 layer (S2) forms on refined metallic surfaces (S1) in a C-Mn0.5Bi0.5 core-shell. A compressed lattice, 9.135 g/cm3 crystal density (up to 2.1% larger from a minima shown at a critical 1.5 wt% C dose), results in the S2 (1-2 nm thickness) tightly interlocks the core-shells in this structure. The XRD patterns, lattice images, and XPS/Raman bands corroborate the features are varied at 0-4 wt% C doses. At a critical 1-2 wt% C dose (a percolation threshold), a maximum energy density (BH)max = 10.30 MGOe (15.35 MGOe at 350 K) is tailored, with a coercivity as much as Hc -> 12.505 kOe (16.015 kOe at 350 K), at room temperature. A 0.03 mu B/C magnetic moment shares a net value, a maximum 66.2 emu/g obtained at 1.7 wt% C. The carbon controls (BH)max and Hc to arise slowly at positive thermal coefficients. The microscopic models insight a way the sp2-C spins integrate collective spin dynamics in the small core-shells in the forms of small clusters. The results are useful for developing material science and technology of this type type rare-earth free ferromagnetic alloys.