Sperimagnetism in Fe78Er5B17 and Fe64Er19B17 metallic glasses: I. Moment values and non-collinear components.

Magnetization measurements have been made on a Fe(64)Er(19)B(17) glass, which exhibits ferrimagnetic compensation at T(comp) = 112 K, and polarized beam neutron scattering measurements have been made on Fe(78)Er(5)B(17) and Fe(64)Er(19)B(17) glasses to supplement the measurements made earlier on Fe(64)Er(19)B(17). The magnetization data were analysed with a phenomenological model, to find the magnetic moments and their components needed to interpret the neutron data. Four spin-dependent scattering cross-sections were obtained in absolute units from each neutron experiment, to determine the atomic-scale magnetic structures of the two glasses. The finite spin-flip cross-sections confirmed that these (Fe,Er)(83)B(17) glasses are non-collinear ferrimagnets. The cross-sections were calculated using a model based on random cone arrangements of the magnetic moments. The moment values and the random cone angles were refined in the calculations, which produced good agreement between the calculated curves and the experimental data. The forward limit of the spin-flip cross-sections |∂σ(±∓)/∂Ω|(Q=0) of the Fe(64)Er(19)B(17) glass which peaked at T(comp) and the temperature variation of the total scattering amplitudes (b(∓)p(∥)(Q)) suggested that the random cone angles open fully so that the collinear components p(∥)(Q) tend to zero at T(comp). The ferrimagnetic compensation is therefore characterized by an equality of the magnetic sublattices; the reversal of the magnetic structure and a compensated sperimagnetic phase which appears at T(comp).

Sperimagnetism in Fe78Er5B17 and Fe64Er19B17 metallic glasses: II. Collinear components and ferrimagnetic compensation.

Magnetization measurements on an Fe(64)Er(19)B(17) glass and polarized-beam neutron scattering measurements on Fe(78)Er(5)B(17) and Fe(64)Er(19)B(17) were described in part I. The finite spin-flip neutron scattering cross sections were calculated using a sperimagnetic structure based on random cone arrangements of the magnetic moments. The temperature variation of the cross sections of Fe(64)Er(19)B(17) suggested that a compensated sperimagnetic phase existed at T(comp).The analysis of the non-spin-flip neutron scattering cross sections is described here in part II. Two spin-dependent total structure factors S(±±)(Q) were defined from these cross sections and, despite the limited range of the data 0.5 Å(-1) < Q < 6.5 Å(-1), their Fourier transform gave reliable spin-dependent radial distribution functions RDF(±±)(r). These were interpreted in terms of the atomic pair correlation functions ρ(±±)(AB)(r) and their weighting factors ω(±±)(AB). The data on Fe(64)Er(19)B(17) at 1.5 K showed, for example, how the directions of the magnetic sublattices can be defined uniquely. The analysis of the RDF(±±)(r) for Fe(64)Er(19)B(17) at 112 K confirmed that the mean collinear components of the magnetic moments , are zero on both sublattices in the compensated sperimagnetic structure at T(comp). The pre-peak in the spin-dependent total structure factors at 112 K showed that it originated in the atomic structure and it may involve Fe-Er-Fe 'collineations' at a radial distance of ≈6.0 Å. Finally, the RDF(±±)(r) of Fe(64)Er(19)B(17) at 180 K and of Fe(78)Er(5)B(17) at 2 K show that both glasses have the (µ(Fe) UP:µ(Er) DOWN) structure like the (Fe,Tb)(83)B(17) collinear ferrimagnets.

Non-collinear ferrimagnetism in a Fe64Er19B17 metallic glass.

Polarized neutron beam measurements on a Fe(64)Er(19)B(17) metallic glass have shown directly that it has a non-collinear magnetic structure. It can be described using a model in which the magnetic moments on the iron atoms point in a random cone that is ferrimagnetically coupled to a random cone of erbium moments, in the manner suggested from bulk measurements. The spin-flip cross-sections were successfully calculated using an optimized choice of the values of the magnetic moments µ(Fe), µ(Er) and the random cone angles θ(Fe), θ(Er). The non-spin-flip cross-sections have an unusual variation with the scattering vector Q, which has not been observed before with transition metal-metalloid glasses. At 1.5 and 60 K the [Formula: see text] cross-section contains a pre-peak at a smaller value of Q (1.3 Å(-1)) than the pre-peaks which have been observed in the structure factors of some transition metal glasses. At 180 K the form of these cross-sections remains the same but the two channels have interchanged, so [Formula: see text] contains the pre-peak. This interchange shows that a complete inversion of the magnetic structure occurs between 60 and 180 K-presumably at the compensation temperature T(comp)≈120 K. Attempts to simulate these cross-sections using the methods applied to (Fe,Tb)B glasses were unsuccessful because none of the known partial structure factors contains a pre-peak which can imitate the observed one. The possible origins of the pre-peak are discussed.