Laila Offernes

The ternary system Au–Mn–Sb and the AuMnSn1−xSbx phase

Abstract The phase relations in the Au–Mn–Sb system have been studied by powder X-ray diffraction, metallography, electron microprobe analysis, and thermal analysis. The condensed phases occurring, tie-lines, and tie-triangles are presented for an isothermal section of the phase diagram at 400 °C. At this temperature the solid solubility of the third component in the binary phases is generally limited to a few percent. The phase relations are relatively complex in regions which involve the numerous binary gold–manganese phases. The only genuine ternary phase, AuMnSb, has a very narrow composition range around Au 35 Mn 30 Sb 35 and is stable up to 575±5 °C, where it decomposes peritectically. The AuMnSb phase is ferromagnetic with a Curie temperature of 135±10 K. The solid-solution phase AuMnSn 1− x Sb x exhibits ferromagnetic properties throughout the entire homogeneity range with the Curie temperature ranging between 625±100 and 135±10 K.

The ternary system Au-Mn-Sn

The phase relations in the Au–Mn–Sn system have been studied by powder X-ray diffraction, metallography, electron microprobe analysis, and thermal analysis. The condensed phases occurring, tie-lines and tie-triangles are presented for an isothermal section of the phase diagram at 400°C. At this temperature the solid solubility of the third component in the binary phases is generally limited to a few percent. The numerous phases in the binary Au–Mn system, are reflected in relatively complex phase relations in certain parts of the Au–Mn–Sn system. The only genuine ternary phase, AuMnSn, has a narrow composition range between Au35Mn31Sn34 and Au33Mn35Sn32 and is stable up to ca. 470°C were it decomposes peritectically.

The crystal structure of AuMnSn

Abstract The crystal structure and magnetic properties of AuMnSn have been studied on single crystals and powders. AuMnSn has a narrow composition range between Au 35 Mn 31 Sn 34 and Au 33 Mn 35 Sn 32 . The unit cell, as determined by single crystal X-ray diffraction, is cubic (space group F43m) with a =632.33(1) pm at 150(2) K, Au in 4c, Mn in 4b and Sn in 4a. There is a certain degree of statistical distribution of Mn and Sn over the 4a and 4b positions, corresponding to 0.10–0.15 Mn on the Sn site and vice versa (the spread reflects the dependence on the different model constraints imposed during the refinements). The crystal structure of AuMnSn is of the AlLiSi type (AgAsMg type when the origin is shifted). Magnetization measurements show that AuMnSn takes a ferromagnetic state from 5 K to above room temperature. AuMnSn is a typical soft ferromagnetic material with a very narrow hysteresis loop and low saturation field (ca. 0.8 T at 5 K). The saturation moment per Mn atom is 3.8 μ B (±0.1 μ B according to repeated measurements) at 5 K and the extrapolated Curie temperature is ca. 600 K.

Prediction of large polar Kerr rotation in the Heusler-related alloys AuMnSb and AuMnSn

Theoretical spectra for the magneto-optical Kerr effect have been obtained for the Heusler-related alloys AuMnSb and AuMnSn, and repeated calculations are performed for the isostructural PtMnSb phase. Using experimental lattice constants, our calculations predict a Kerr rotation exceeding −1° in the 0.5–0.8 eV region for AuMnSb and a somewhat smaller rotation for AuMnSn. Supercell calculations indicate that half-metallic behavior can be induced on hole/electron doping in the AuMnSn1−xSbx solid-solution phase for 0.50

The tin-rich part of the Au–Pt–Sn system

Abstract The phase relations in the tin-rich section (≥50 at.% Sn) of the system Au–Pt–Sn have been studied by powder X-ray diffraction, metallography, electron microprobe analysis and thermal analysis. The condensed phases occurring, tie-lines and tie-triangles are presented for an isothermal section of the tin-rich part of the phase diagram at 400°C. There is a limited solid-solubility exchange between Au and Pt in most of the binary phases; however, for AuSn and Pt 2 Sn 3 the ranges of homogeneity are appreciable. Up to 50% of the gold in AuSn can be replaced by platinum and up to ca. 20% of the platinum in Pt 2 Sn 3 can be replaced by gold. A new ternary phase (attributed the formula AuPt 2 Sn 4 ) has also been discovered, with a homogeneity range in the Au–Pt dimension between Au 137 Pt 293 Sn 570 and Au 196 Pt 241 Sn 563 . AuPt 2 Sn 4 is C -centred monoclinic with unit-cell dimensions a =543.1(1), b =527.4(1), c =931.3(1) pm and β =101.17(1)°.

On the ferromagnetism of AuMnSn

Abstract The ferromagnetic ordering of the Heusler-related alloy AuMnSn has been verified by powder neutron diffraction. The cubic AlLiSi-type crystal structure of AuMnSn [ a =634.12(11) pm at 298 K, Au in 4 c , Mn in 4 b , Sn in 4 a of F 43 m ] has been confirmed. Contrary to the indications from the preceding single-crystal X-ray diffraction study of AuMnSn the powder neutron diffraction data gave no evidence for intermixing of Mn and Sn on the 4 b and 4 a sites. The ordered magnetic moments are confined to the Mn atoms and their size at 298 K is μ F,Mn =3.62(7) μ B .

Comment on “Optical and magneto-optical properties of AuMnSn” [Appl. Phys. Lett. 88, 121909 (2006)]

It has recently been reported that the experimental maximum Kerr rotation and ellipticity for AuMnSn are shifted 0.6 eV higher in energy than that predicted from our full-potential densityfunctional calculation. Similarly the intensity of the measured Kerr rotation spectra turned out to be about three times smaller than our predicted values and it was argued that the failure of the local spin-density approximation to account for the correlation effect is responsible for these discrepancies. However, the magneto-optical Kerr effect measurements were made at room temperature on nonstoichiometric crude single crystals, whereas our calculated spectra are valid for ideal stoichiometric single crystals at low temperatures. The temperature effect is one of the main reasons for the discrepancies, but we have also discussed other possible reasons.