G. B. Street

Transport properties of vapor grown orthorhombic sulfur crystals

Abstract Crystals of orthorhombic sulfur have been grown from the vapor phase and their electrical transport properties are compared with those of CS 2 solution grown and natural sulfur crystals. The temperature dependence of the hole drift mobilities shows that the transport mechanism is trap controlled. The trap depth in the vapor grown crystals is 0.22 eV which is the same as that for the solution grown crystals. However, the trap density (10 17 cm −3 ) in the vapor grown crystals is 1–4 orders of magnitude higher than found in the solution grown crystals. The trap is attributed to a structural defect in both types of crystal. The electron transport is by an intermolecular hopping process 3 which becomes trap controlled at lower temperatures. The trap depth and density are 0.4±0.1 eV and 10 14 cm −3 respectively. Thermally stimulated conductivity measurements have been made on vapor grown, solution grown and natural crystals. Peaks at 0.17 eV and 0.2 eV are correlated with electron and hole mobility activation energies respectively.

Stabilization of the high−temperature phase of MnBi by the addition of rhodium or ruthenium

It has been found that adding Rh or Ru to MnBi is effective in stabilizing the high−temperature β phase (distorted NiAs structure) relative to the low−temperature α phase (undistorted NiAs structure). This effect has been observed in both evaporated thin films and bulk samples. Addition of 1 at.% Rh to bulk MnBi increases the minimum time constant for the β→α transformation by 5 orders of magnitude. Stabilization is important in the use of MnBi for thermomagnetic recording.

The influence of 3d transition metal substitution on the magnetic properties of MnGaGe

Abstract A study has been made of the effect of 3 d transition element substitution on the magnetic moment and Curie temperature of MnGaGe. Substitution of 3 d elements with atomic number less than Mn (i.e. Ti, V, or Cr) cause relatively small changes in magnetic properties, whereas substitution of Fe, Co, Ni and Cu cause a large reduction in moment and Curie temperature, e.g. substitution of 5 at.% Fe for Mn causes the moment to decrease by 30 per cent. The moment and ferromagnetism of MnGaGe are described in terms of a band model involving both strongly correlated and intinerant 3 d electrons. The effect of 3 d element substitution may be qualitatively understood in terms of this model.

The stabilization of the high temperature phase of MnBi by the addition of rhodium or ruthenium

Manganese bismuth has long been considered as a material for use in thermomagnetic recording. It exists as a low temperature phase α and high temperature phase β, of which the β phase is more attractive for thermomagnetic applications as it requires only about 1/4 of the writing energy required for the α phase.1. The principal problem associated with the β phase is that it tends to convert to the more stable α phase on thermal cycling. Stabilization is therefore an important problem which has received much attention. It has been found that rhodium and ruthenium are effective in stabilizing both thin films and bulk samples of B‐MnBi. Addition of 1 at.% Rh in bulk MnBi increases the minimum time constant for the β→α transformation by five orders of magnitude and lowers the transformation temperature from 360°C to 326°C. Films of nominal composition Mn0.89Rh0.16Bi showed no evidence of transformation for temperatures up to 250°C even after 106 secs.

Magnetic Properties of the New Magnetic Compounds Mn‐X‐Bi (X = Ni, Cu, Rh, Pd)

A new group of magnetic compounds has been discovered in the ternary system Mn ‐ X ‐ Bi where X is Ni, Cu, Rh or Pd. The compositions of these compounds are Mn 5 Ni 2 Bi 4 , Mn 3 Cu 4 Bi 4 , Mn 5 Rh 2 Bi 4 , and Mn 5 Pd 2 Bi 4 . Each sample was found by differential thermal analysis to be stable to at least 500°C. The X‐ray powder diffraction data do not correlate with any known crystal structures. A new structure is proposed for these compounds which has a face‐centered cubic Bravais lattice and 88 atoms/unit cell. This structure may be characterized by substantial distortion of Mn, X and Bi atoms relative to empty octahedral sites. The space group is Fm3m. Susceptibility measurements suggest that these compounds are predominantly ferromagnetic. The Curie temperatures are −7°C(Rh), 54°C(Pd), 101°C(Ni), and 183°C(Cu).

Magnetic Properties of the New Magnetic Compounds

A new group of magnetic compounds has been discovered in the ternary system Mn ‐ X ‐ Bi where X is Ni, Cu, Rh or Pd. The compositions of these compounds are Mn 5 Ni 2 Bi 4 , Mn 3 Cu 4 Bi 4 , Mn 5 Rh 2 Bi 4 , and Mn 5 Pd 2 Bi 4 . Each sample was found by differential thermal analysis to be stable to at least 500°C. The X‐ray powder diffraction data do not correlate with any known crystal structures. A new structure is proposed for these compounds which has a face‐centered cubic Bravais lattice and 88 atoms/unit cell. This structure may be characterized by substantial distortion of Mn, X and Bi atoms relative to empty octahedral sites. The space group is Fm3m. Susceptibility measurements suggest that these compounds are predominantly ferromagnetic. The Curie temperatures are −7°C(Rh), 54°C(Pd), 101°C(Ni), and 183°C(Cu).

Magnetic Properties of the New Magnetic Compounds Mn‐X‐Bi(X = Ni, Cu, Rh, Pd)

A new group of magnetic compounds has been discovered in the ternary system Mn ‐ X ‐ Bi where X is Ni, Cu, Rh or Pd. The compositions of these compounds are Mn 5 Ni 2 Bi 4 , Mn 3 Cu 4 Bi 4 , Mn 5 Rh 2 Bi 4 , and Mn 5 Pd 2 Bi 4 . Each sample was found by differential thermal analysis to be stable to at least 500°C. The X‐ray powder diffraction data do not correlate with any known crystal structures. A new structure is proposed for these compounds which has a face‐centered cubic Bravais lattice and 88 atoms/unit cell. This structure may be characterized by substantial distortion of Mn, X and Bi atoms relative to empty octahedral sites. The space group is Fm3m. Susceptibility measurements suggest that these compounds are predominantly ferromagnetic. The Curie temperatures are −7°C(Rh), 54°C(Pd), 101°C(Ni), and 183°C(Cu).