N.A. Smith

Structural, magnetic and constitutional studies of a new family of ternary phases based on the compound Fe3GaAs

Abstract The compound Fe3GaAs has been identified as a B82-type (hexagonal) phase which exists over a range of compositions represented by the general formula Fe3Ga2 − xAsx (0.875 ⩽ x ⩽ 1.125). For x ⩽ 0.85 there is a change in structure to another, closely related hexagonal modification which persists to x ≈ 0.21 and in which there is a doubling of the a spacing compared with that of the earlier structure. All the alloys are ferromagnetic∗ in nature with a marked rise in the Curie temperature with increasing gallium content. Curie temperatures as high as 644 K have been achieved in these alloys. There is a corresponding general increase in the Ms values but there is a dip at the composition where there is a change in the structure. Mossbauer measurements on the alloys are in agreement with the magnetic and structural data.

Phase identification in Fe-doped GaAs single crystals

Phase analysis has been carried out on Fe-doped LEC single crystals of GaAs in order to determine the nature of the precipitates which form once the solid solubility limit of Fe in GaAs is exceeded. SEM studies have shown that a eutectic is formed in the lower parts of the crystal to solidify. LINK/EDX and magnetic measurements indicate that this eutectic consits of a previously unidentified ternary compound Fe3GaAs, and GaAs containing Fe. Magnetic measurements on the eutectic mixture and on a specially prepared sample of Fe3GaAs indicate that this new phase is ferromagnetic with a Curie temperature around 100°C.

The identification of precipitate phases in Fe-doped InP single crystals

Abstract The nature of precipitates found in Fe-doped single crystals of InP grown by the LEC method has been investigated. SEM studies show that the precipitates have only one type of morphology namely, a rhombohedral shape whilst back-scattered electron and EDAX investigations establish that a significant proportion of the precipitates are two-phase mixtures of FeP 2 and FeP. This phase analysis is confirmed by gravimetric studies. The two-phase nature of the iron-phosphide precipitation explains inconsistencies in published X-ray data for these precipitates.

Structural identification of the new magnetic phases Fe3Ga2−xAsx

X-ray diffraction and Mossbauer studies have been used to identify precisely the crystal structure of recently discovered ferromagnetic alloys based on a series of Fe3Ga2−xAsx (0.21 ⩽ x ⩽ 1.125) alloys. In particular, it is shown that the change in structure from a B82 type to a more ordered variant which occurs with increasing gallium content at x ≈ 0.85, is consistent with an ordering process associated with vacant iron sites. Comparison is also made between the lattice spacing data of as-cast and homogenized alloys.

Precipitate identification in co-doped InP

Abstract The nature of precipitates found in Co-doped single crystals of InP grown by the LEC method has been investigated using scanning electron microscopy (both secondary and back scattered electrons and energy dispersive X-ray analysis (EDAX)) and Debye–Scherrer X-ray diffraction. Two phases have been detected. One has been positively identified as the cubic CoP 3 phase and was found to exist in two distinct morphologies, as cuboids at and near to the surface of the crystal and as fine rods in a eutectic CoP 3 -InP mixture within the bulk of the crystal. in some crystals another phase has been observed which is also a cobalt phosphide but significantly more Co-rich than CoP 3 . Thus far, the crystal structure of this phase has not been identified.

Precipitate identification in Ti-, Cr- and Ni-doped InP single crystals

Abstract The phases which precipitate due to normal segregation in the LEC growth of Ti- or Ni-doped InP are shown respectively to be TiP and Ni 2 P, whilst the precipitating phase in Cr-doped InP is confirmed as CrP. The relevance of this phase identification to the general pattern of precipitation behaviour in transition metal (First Long Period) doped InP is reviewed.

Metalorganic chemical vapour deposition of manganese arsenide for thin film magnetic applications

Abstract Thin films of the ferromagnetic material manganese arsenide (MnAs) have been grown for the first time by atmospheric pressure metalorganic chemical vapour deposition (MOCVD), using tricarbonylmethylcyclopentadienyl manganese (TCM) and arsine. A detailed study of the MnAs growth characteristics are presented together with the resulting magnetic and structural properties.

Precipitate identification in LEC-grown Si-doped GaAs

It is shown that the phase which precipitates due to normal segregation in LEC-grown Si-doped GaAs, once the solid solubility of the dopant is exceeded, is elemental Si. The presence of high Si concentrations in the melt also promotes the formation of a further precipitate which appears at the melt-encapsulant interface and also becomes incorporated into the crystal surface. This precipitate has been identified as B13As2.

Identification of a new cobalt phosphide phase as a precipitate in LEC single crystal InP

A previously unreported orthorhombic phosphide of cobalt, CoP2, has been identified as a precipitate in Co-doped LEC single crystal InP and X-ray diffractions studies show that this phase has the FeS2-type structure, i.e. it is isomorphous with FeP2. The fact that CoP2 does not exist as an equilibrium phase in the CoP system, is confirmed by vaporisation studies of CoP3 precipitates which decomposed directly to the orthorhombic CoP phase. Electron backscattered investigations reveal that some of the CoP2 precipitates are partially decomposed and consist of a mixture of CoP and InP. The composition of the phosphides and the instability of CoP2 have been established by transmission electron microscopy.

The identification of precipitates in v-doped InP single crystals

Abstract Precipitates which form in vanadium-doped single crystals of indium phosphide during LEC growth are shown to be the hexagonal phase, vanadium monophosphide.