Noncollinear spin structure in Fe3+xCo3−xTi2 (x=0,2,3) from neutron diffraction

Neutron powder diffraction has been used to investigate the spin structure of the hard-magnetic alloy $\mathrm{F}{\mathrm{e}}_{3+x}\mathrm{C}{\mathrm{o}}_{3\ensuremath{-}x}\mathrm{T}{\mathrm{i}}_{2}$ ($x=0,2,3$). The materials are produced by rapid quenching from the melt, they possess a hexagonal crystal structure, and they are nanocrystalline with crystallite sizes $D$ of the order of 40 nm. Projections of the magnetic moment onto both the crystalline $c$ axis and the basal plane were observed. The corresponding misalignment angle exhibits a nonlinear decrease with $x$, which we explain as a micromagnetic effect caused by Fe-Co site disorder. The underlying physics is a special kind of random-anisotropy magnetism that leads to the prediction of $1/{D}^{1/4}$ power-law dependence of the misalignment angle on the crystallite size.