Muon hyperfine fields in iron and its dilute alloys

The temperature dependence (240 to 633 K) of the interstitial magnetic field, B_μ, as determined by the rotation of the spin of the μ⁺, has been measured for dilute polycrystalline iron alloys with Mo, Ti and Nb additions. In all cases the behaviours differ from one another and from the Fe(A1) alloys previously studied. B_μ, which is negative with respect to the magnetization, is increased in magnitude by A1 and Mo, and decreased greatly by Ti. The addition of Nb creates a two- phase alloy from which we can assess the role of heterogeneity and/or strain on B_μ in iron. If the temperature dependence of the hyperfine field B_hf extracted from B_μ for Fe(Mo) alloys is interpreted on the model previously used to discuss the Fe(A1) data, we would conclude that the muon is attracted to the Mo atom while repelled by the A1 atoms as the temperature decreases. Measurements giving room temperature values of B_μ for iron alloys with Mn, Cr, V and W taken after annealing above the recrystallization temperature are also reported.