Olaf Muller

FeBO3 solid solutions: Synthesis, crystal chemistry, and magnetic properties☆

Abstract Solid solutions of the type Fe1−xMxBO3 have been prepared where M = Mn, Cr, Al, Ga, or In. For M = In, Ga, or Cr, x can vary from 0 to 1.0, but the solid solution range is more restricted for M = Al (O ≤ x ≤ 0.32) and Mn (O ≤ x ≤ 0.10). The present investigation of these materials includes their crystal chemistry, thermal stability, and magnetic properties. The calcite-type unit-cell parameters follow closely Vegards Law. DTA results indicate that the thermal stability increases with increasing M content for M = Cr, Al, or In. Room-temperature magnetic measurements show that the Fe1−xMxBO3 phases remain canted antiferromagnets up to the 20 to 30% substitution level, with monotonic decrease in the magnetization and Curie temperature as a function of the concentration of M (dilution effect). Low-temperature magnetic studies of the systems Fe1−xCrxBO3 and Fe1−xInxBO3 show anomalous magnetic behavior at the higher Cr and In concentrations.

δ-FeO (OH) and its solutions

Decomposition products of δ-FeO(OH)-type Fe1−xMxO1−x(OH)1+x phases (M=Mg, Zn, Ca, Cd) have been studied by X-ray diffraction, electron diffraction and high-resolution transmission electron microscopy. It has been shown that the M=Mg and Cd δ-phases decompose to α-Fe2O3-based solid solutions which in turn undergo exsolution to form some MgO and CdO at a higher temperature. In the case of Fe1−xZnxO1−x(OH)1+x, the decomposition proceeds over α-Fe2O3 ss to an unstable spinel solid solution. All decomposition products are topotactically related to their precursors in the decomposition chain. In the electron microscope some δ-type phases undergo in situ decomposition under intense beam bombardment with somewhat different results than obtained for thermal decomposition products under ambient conditions. The plate-like morphology and crystal size is retained in the decomposition products; however, the products have a more pitted appearance after decomposition.

?-FeO(OH) and its solid solutions: Part 2 High resolution transmission electron microscopy of pure ?-FeO(OH)

A transmission electron microscope imaging investigation was performed on small δ-FeO(OH) crystallites less than 50 Å thick and several hundred angstroms across. We have observed faceting, and a hexagonal plate-like morphology with topological features near atomic step heights. Because of the mutual magnetic attraction on these particles, they tend to align with their thin direction (c-axis) either parallel or perpendicular to the support film surface. It is therefore possible to view dislocations or buckling of lattice planes of these plates either edge-on or perpendicular to this direction by direct lattice imaging in both the bright-field and dark-field modes. A highly distorted lattice is apparent when viewing the particles edge-on, and it is possible to show lattice projections to a resolution of 2.1 Å.

Magnetization studies in the system Fe1−xCrxBO3

Temperature‐dependent magnetization studies from 4.2 to 600 °K have been made for the solid solution system Fe1−xCrxBO3 where 0⩽x⩽0.95. A rapid decrease is observed in the saturation magnetization with increasing x at 4.2 °K up to 0.40, after which a broad compositional minimum is found up to x=0.60. Compositions in the range of 0.40⩽x⩽0.60 display unusual magnetization behavior as a function of temperature in that maxima and minima are present in the curves below the Curie temperatures. Possible explanations for these anomalies are discussed.

A fine-particle transmission electron microscope investigation of CrO2 and CrO(OH)

Abstract A transmission electron microscope imaging and diffraction investigation has been performed on small CrO2 crystallites. The acieular crystal morphology has been observed and electron-diffraction evidence is presented which indicates the presence of a very thin CrO(OH) layer of 6-13 A. CrO2 has been partly converted topotactically to orthorhombic CrO(OH) in hot water and single-crystal electron-diffraction evidence is used to establish this topotactic relationship. Under sufficiently high temperatures or electron-beam irradiation, CrO2 and CrO(OH) convert topotactically to Cr2O3, as seen from single-crystal electron-diffraction data. This last conversion is further characterized using high-resolution dark-field microscopy which reveals the presence of interference patterns from the formation of microcrystalline domains.

Compositional analysis of pattern-plated permalloy films

Abstract The combination of scanning electron microscopy (SEM)—energy-dispersive spectroscopy (EDS) and secondary ion mass spectrometry (SIMS) is a powerful approach for the characterization of the lateral and depth homogeneity of pattern-electroplated permalloy (Ni 0.80 Fe 0.20 ) films. SEM-EDS is particularly useful for providing highly accurate data on a large number of analysis points for lateral homogeneity characterization. SIMS proved particularly useful in providing depth profiles with high depth resolution.