N. Kataoka

Magnetic properties of high-concentration Fe-Ag alloys produced by vapour quenching

Alloys of Fe1-xAgx obtained by vapour quenching have been investigated by X-ray diffraction and magnetisation measurements. The single BCC phase extends up to about x=0.14, while the single FCC phase exists above x=0.6. For x=0.14-0.6, there is a mixed BCC and FCC phase. The average magnetic moment decreases with increasing x. It deviates upwards from the simple dilution law in the BCC and FCC alloys with x=0.6-0.7. The Curie temperature, TC, is about 900K for the BCC alloy with x=0.1, while TC is about 550K for the FCC alloy with x=0.6 and decreases with increasing x to zero at about x=0.95.

Nonequilibrium crystalline Fe-Ag alloys vapour-quenched on liquid-nitrogen-cooled substrates

Fe1-xAgx alloys vapour-quenched on liquid-nitrogen-cooled substrates have been investigated by X-ray diffraction, magnetisation and Mossbauer effect measurements. The single BCC phase extends up to x=0.2 and the single FCC phase down to x=0.45. These single-phase regions are much wider than those of the Fe1-xAgx alloys deposited on water-cooled substrates and no amorphous phase has been obtained over the whole range of concentration. In the Mossbauer spectra, an analysis of the broad quadrupole splitting indicates that the atomic configurations of the FCC Fe-Ag alloys deposited on liquid-nitrogen-cooled substrates are more randomised than those deposited on water-cooled substrates.

Thermal stability of nonequilibrium crystalline FeAg alloys produced by vapor quenching

X-ray diffraction and Mossbauer effect measurements were made for sputter-deposited Fe-Ag alloys after isochronal and isothermal annealings. Below 570 K, the metastable b.c.c. and f.c.c. single phases undergo a structural relaxation. Above 570 K, these metastable phases decompose by ejecting supersaturated Ag or Fe atoms. During the heating processes of the f.c.c. alloys, the ejected Fe atoms form clusters and then transform to b.c.c. particles as their sizes grow beyond a critical value. The index n in the Johnson-Mehl-Avrami plot is about 0.65.

Non-equilibrium Ag-TM alloys produced by vapour quenching (TM ≡ Cr, Mn, Fe and Co)

Abstract AgCr, AgMn, AgFe and AgCo alloys were produced by a sputter-deposition method. Wide ranges of primary solid solutions were formed on water-cooled substrates, although the equilibrium phase diagrams of these alloys are immiscible except for AgMn. In AgFe alloys, the single-phase body-centered cubic (b.c.c.) and face-centred cubic (f.c.c.) regions were greatly extended on liquid-nitrogen-cooled substrates. The phase boundaries of silver-rich f.c.c. phases are roughly consistent with the results estimated from the classical elastic model.

Thermal stability of high concentration Fe-Ag and Fe-Cu alloys produced by vapor quenching

Mössbauer effect measurements were carried out for sputtered fcc Fe-Ag and Fe-Cu alloys annealed at various temperatures. At temperatures higher than 300 °C, the metastable fcc phases decompose by removing saturated Fe atoms. During the phase separation processes, the ejected Fe atoms form clusters, which initially have a fcc structure and transform to bcc particles as their sizes grow beyond a critical value.

Thermal Stability of Nonequilibrium Fe-Ag and Fe-Cu Alloys Produced by Vapor Quenching

X-ray diffraction and Mössbauer effect measurements were carried out for sputtered fcc Fe-Ag and Fe-Cu alloys after being annealed at various temperatures. At temperatures higher than 300°C, the metastable fcc phase decomposes by removing supersaturated Fe atoms. In the fcc Fe-Ag alloys, Fe atoms always give a ferromagnetic hyperfine field component during the clustering process. On the other hand, in the fcc Fe-Cu alloys, the supersaturated Fe atoms form clusters and behave as ¿-Fe, giving a small, hyperfine field component.

Evaluation of Magnetic Perpendicular Anisotropy of Vapor Quenched Fe Films Using Mössbauer Effect

Pure Fe films were produced by rf sputtering under several Ar gas pressures and were investigated with an SEM and Mössbauer effect. In the Mössbauer spectra, a perpendicular magnetic anisotropy was observed for films made under high Ar gas pressures, while an in-plane anisotropy was seen for films made under low Ar gas pressures. The anisotropy of the films did not change after one hour of annealing at 300 K. Films made under low Ar gas pressures have a fine fiber structure, while films made under high Ar gas pressures have a columnar structure separated by distinct boundaries. Assuming that the magnetic interaction within the columnar structure is weak, the perpendicular magnetic anisotropy of the films under high Ar gas pressures can be explained by the shape anisotropy of the columnar structure.