Bertil Carlsson

Determination of the homogeneity range and refinement of the crystal structure of Fe2P

Abstract The homogeneity range of Fe2P has been determined using the annealing and quenching technique in combination with X-ray powder diffraction methods. The iron-rich limit is invariant at Fe2.00P for temperatures up to 1150°C. The phosphorus-rich limit varies from Fe2.00P at low temperatures to Fe1.94P at 1100°C. The crystal structure of Fe2.00P has been refined from X-ray diffraction data obtained by single-crystal diffractometry. The thermal vibrations differ appreciably in magnitude for the two non-equivalent types of iron atom.

First order magnetic transition, magnetic structure, and vacancy distribution in Fe2P

Abstract The para- to ferromagnetic transition in Fe 2 P has been studied using Mossbauer spectroscopy. The magnetic hyperfine fields drop abruptly from about half of their saturation values to zero at 214.5 K indicating a first order transition. The isomer shifts show a discontinuous change at the transition point. For some samples the transition takes place over a wide temperature range, probably due to impurities and other imperfections in the samples. From the magnetic hyperfine fields at 15 K the magnetic moments can be deduced to be 1.14 μ B and 1.78 μ B for Fe(1) and Fe(2), respectively. An assignment of the components in the Mossbauer spectra to the two crystallographically nonequivalent iron positions has been made from the temperature variation of the spectra. The ordering of metal vacancies has been investigated by a Mossbauer study of a nonstoichiometric Fe 2 P sample and by an X-ray diffraction study of a nonstoichiometric Mn 2 P crystal.

First Order Magnetic Phase Transition in Fe2P

The magnetic properties of stoichiometric Fe2P and non-stoichiometric Fe2-xP (0 < × ≤ 0.06) have been studied by means of magnetic susceptibility. Measurements on pure stoichiometric Fe2P samples show that there is a first order magnetic phase transition from a ferro- to a paramagnetic state at 216 ± 1 K. The transition is accompanied by a discontinuous change in the dimensions of the hexagonal unit cell with a decrease in the a-axis of 0.06% and an increase in the c-axis of 0.08% for increasing temperature. The transition is interpreted to be of magnetoelastic origin with an exchange energy critically sensitive to the interatomic spacing. Measurements on single crystals show that the spins are directed along the hexagonal c-axis with an exceedingly high axial anisotropy. The saturation moment is 1.46 μB/iron atom and the anisotropy energy as estimated from low field data is ~ 2.5 × 106 J m-3 (2.5 × 107 erg cm-3). The transition behaviour is very sensitive to the magnitude of the external field as well as to the presence of impurities and deviations from the ideal stoichiometry in the samples.

Magnetic and Electric Properties of FeP2 Single Crystals

Measurements of the magnetic susceptibility, electrical resistivity and Hall effect have been made on FeP2 single crystals prepared by a chemical transport reaction. FeP2 is a diamagnetic semiconductor with a nearly temperature independent susceptibility of -(8.8±0.7)10-6SI (at room temperature), and a band gap of 0.37 eV.

The crystal structure of Hf3As

Abstract Hf3As has a monoclinic unit cell of dimensions a = 15.3898(14) A, b = 5.3795(5) A, c = 15.330(14) A, β = 90.291(6)°. A structure proposal based on space group C2 c (No. 15) has been refined by the least-squares method using a Rietveld-type fullprofile analysis of Guinier-Hagg X-ray powder film intensity data. The Hf3As structure is an intermediate between the Fe3P and the Ti3P types. The atomic coordination follows rules formulated earlier for representatives of the Fe3PTi3PV3S family of structures.

Magnetic Susceptibility Resistivity and Thermal Expansion Measurements on FeP

Susceptibility, resistivity and thermal expansion measurements have been performed on single crystals of FeP. The temperature ranges were 4.2 K-300 K, 15 K-300 K and 95 K-300 K respectively. The susceptibility measurements show a magnetic transition at 120 K, which is due to an antiferromagnetic ordering in the ab-plane. Above TN there is a considerable amount of anisotropy. The susceptibility curves representing the three principal directions have maxima around 220 K. The magnetic structure is interpreted in terms of a linear chain model. This interpretation of the experimental results is based on the theoretical work by Kallel et al. Resistivity measurements, carried out with the van der Pauw method, give an anisotropic resistivity tensor. The resistivity vs. temperature curves have points of inflexion at 115 K. The thermal expansion coefficient of the b-axis is much larger than the coefficients of the other axes.