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 Fe3+xCo3-xTi2 (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.