M. Biernacka

Determination of the Riemann modulus and sheet resistivity by a six-point generalization of the van der Pauw method

Six point generalization of the van der Pauw method is presented. The method is applicable for two dimensional homogeneous systems with an isolated hole. A single measurement performed on the contacts located arbitrarily on the sample edge allows to determine the specific resistivity and a dimensionless parameter related to the hole, known as the Riemann modulus. The parameter is invariant under conformal mappings of the sample shape. The hole can be regarded as a high resistivity defect. Therefore the method can be applied for experimental determination of the sample inhomogeneity.

Electric and Magnetic Properties of bcc Fe Based Multicomponent Alloys

The electrical and magnetic properties of a bcc Fe 1- x A x , system with the average atom formed by A = (Al, Si, V, Cr) are presented. Compositions were chosen to obtain alloys of simple structure with control parameter ( x ) covering some important Heusler alloys. Systematic changes in the residual resistivity, magnetic moments, and electronic structure with concentration x are observed. The so-called parallel-resistivity formula ρ -1 =ρ ideal -1 +ρ sat -1 was used for quantitative characterization of the concentrated alloys, where ρ ideal denotes a contribution resulting from different mechanisms of scattering and ρ sat represents a shunt resistivity. At small concentrations x , the main contribution comes from structural disorder. It is shown that the density of states at the Fermi level is substantially reduced at larger x in agreement with results of electronic structure calculations.

Magnetism of UFe4−xAl8+x (x=〈−0.4, 0.4〉) intermetallics

Abstract Results of X-ray, neutron diffraction, magnetization and Mossbauer measurements with circularly polarised beam on polycrystalline samples of the ternary intermetallic alloys UFe 4− x Al 8+ x with x in the range (−0.4, 0.4) are presented. The alloys crystallise in the structure of ThMn 12 type, belonging to the space group I4/mmm (no. 139). X-ray and neutron diffraction confirmed the phase homogeneity of all samples but that one with 4− x =4.4. Monochromatic Circularly Polarised Mossbauer Source (MCPMS) measurements reveal spin-canted magnetic structures in randomly oriented powders exposed to a field of 1 T at T=12 K. Magnetization measurements in an external field of 0.01 T allowed disclosing ferromagnetic-like behaviour vs. temperature and quite dissimilar magnetization and hysteresis curves against the fields in the alloys of interest.

Magnetic and structural properties of Fe3−xCrxAl0.5Si0.5

Results of X-ray, neutron, magnetization and M?ssbauer measurements on polycrystalline samples of Fe3?xCrxAl0.5Si0.5 (x = 0, 0.125, 0.250, 0.375 and 0.5) alloys are presented. The alloys crystallize in the structure of DO3 type, and their unit cell volumes are practically independent of the chromium concentration. X-ray and neutron diffraction confirmed the phase homogeneity of all the samples. Neutron and Mossbauer measurements disclosed that Cr atoms occupy preferentially B-sites, while D sites are almost entirely occupied by Al and Si. The total magnetisation as well as the site and individual magnetic moments ?Fe(A,C), ?Fe(B) and ?Cr(B,D) have been found to be linearly dependent on the chromium concentration.

Iron Atoms in Cr–Mn Antiferromagnetic Matrix

The results of the Mössbauer effect measurements on bcc Cr rich Cr-Fe-Mn alloys in temperature range 12–296 K in zero- and in applied magnetic fields are reported. Monochromatic, circularly polarized radiation was used for investigation of iron moments alignment. Strong enhancement of internal hyperfine magnetic field induced by the applied magnetic field was detected and explained as due to dynamical effects. At high temperatures alignment of iron moments in antiferromagnetic phase is weakly magnetic field-dependent. At low temperatures the average hyperfine magnetic field is antiparallel to the net magnetization showing that iron moments are partly ordered by the applied field.

Phase composition and magnetism of sol–gel synthesized Ga–Fe–O nanograins

ABSTRACT We have succeeded in synthesizing orthorhombic Ga(1−x)Fe(1+x)O3 (−0.05 x0.5), hexagonal GayFe(2−y)O3 (0y1.8) and cubic Ga(1+z)Fe(2−z)O4 (−0.1z0.8) nanograins of gallium ferrites using conventional precursors and an organic environment of Pechini scenario under atmospheric-pressure conditions (SG method). Phase composition and homogeneity were analyzed using X-ray diffraction. Small angle neutron scattering disclosed ellipsoidal particle shapes of gallium iron oxides (GFO) crystallizing in orthorhombic (o-GFO) and hexagonal (h-GFO) symmetry and parallelepiped shapes of Ga(1+y)Fe(2−y)O4 (c-GFO) grains. Despite local agglomeration among the magnetic grains, the scanning electron microscopy and transmission electron microscopy images point to faced-elliptical shapes. The Mössbauer spectroscopy with magnetization measurements was carried out in the temperature range of 5–295 K. The analysis of gallium ferrites magnetism demonstrates that iron atoms locate with various probabilities in crystallographic positions and the spontaneous magnetization preserves up to room temperature (RT).

The Resistivity and Hall Effect of the Amorphous Co_{x}Ni_{70-x}Fe_{5}Si_{15}B_{10} Ribbons

The influence of structural disorder and magnetism on the resistivity of the amorphous CoxΝi70-x Fe5 Si15 Β 10 ribbons was investigated. The resistivity vs. alloy composition shows parabolic-like behaviour. In the thermal behaviour, resistivities of the samples show apparent magnetic contribution. They also exhibit minima at temperatures which can be correlated with the Curie temperatures. Above Τ > 0.5ΤC resistivity increases linearly with increasing temperature. This effect is seemingly due to electron-phonon scattering. Obviously, the chemical and positional disorder is responsible for the major part of resistivity.