Fe–Mn mechanically alloyed powders characterised by local probes

Abstract

High-energy ball milling of Fe–Mn elemental powder mixtures has been carried out for Mn atomic concentrations in the range 10–90%. X-ray diffraction (XRD), Mössbauer spectroscopy (MS) and perturbed angular correlations (PAC) have been used to investigate the crystalline structure in the milled samples. It is found that ball milling gives rise to concentration ranges of existence of terminal solid solutions more extended than in the equilibrium phase diagram. Particular attention has been paid to the environment of 57Fe (MS) and 111In (PAC) probe atoms: 57Fe atoms are a constituent of the system, while 111In atoms have been implanted at 400 keV into pills made from the milled powders. The PAC spectra of milled Fe show the ferromagnetic α-phase with a high fraction of a single vacancy next to the probe. Accordingly, the Mössbauer spectrum is a sextet with the characteristic splitting of α-Fe and a broadening which indicates a certain degree of atomic structure disorder. With an amount of Mn up to 15% PAC probes with one and two Mn next neighbours are identified by their smaller magnetic hyperfine field, corresponding to two distinct magnetic components in the Mössbauer spectra. At 20 and 30% of Mn the PAC magnetic signal of the a-phase disappears in favour of a distorted cubic apparently non-magnetic signal. From 40 to 70% of Mn a broad distribution of hyperfine magnetic fields is observed by PAC. Mössbauer spectra in the 20–70% of Mn range can be fitted with an unresolved low field magnetic sextet. Finally, the PAC spectra at 80 and 90% are quite similar to the one which is obtained after milling pure Mn, while the corresponding Mössbauer data can be roughly approximated to those of the α-Mn(Fe) solid solution.