A. Nakanishi

Magnetism of Cr in V/Cr multilayers studied by 119Sn Mössbauer spectroscopy

The magnetic properties of thin Cr layers in epitaxial V/Cr multilayered structures were investigated at room temperature and 15 K via 119Sn Mossbauer spectroscopy. The magnetic moment and the Neel temperature of Cr, as inferred from the magnetic hyperfine fields transferred to the 119Sn monatomic layers inserted in Cr layers, were found to reduce on decreasing the Cr layer thickness below 40 A. The local magnetic structure along the growth direction of 80 A thick Cr layers was investigated by changing the Sn probe positions. The effect of the V/Cr interface on the Cr magnetism is discussed.

Hydrogen-filled proportional counter operated at low temperatures and its application to CEMS

Abstract The operation of a proportional counter filled with hydrogen gas was investigated at temperatures between 15 K and room temperature. It was found to work stably at any temperature in this range. This counter was then applied to conversion electron Mossbauer spectroscopy (CEMS).

Proportional counter operated at 13–300 K and its application to CEMS

The operation of a proportional counter was investigated at temperatures between 13–300K. It was found that the suitable gases filled in the counter are purified belium at temperatures below 22K, purified neon at temperatures between 22–53K and He+5%N2 or He+10%CO at temperatures above 46 or 47K, respectively. This experimental technique was applied to CEMS with natural iron and with a thin foil of iron oxide.

Magnetic properties of iron-oxide small particles prepared on aluminum and MgO(100)

Abstract Magnetic properties of small particles of iron oxide on an aluminum foil and a single crystal of MgO are studied by conversion electron Mossbauer spectroscopy (CEMS) at low temperature. The average thickness of the oxide layers is 3.0 nm on aluminum and 1.2 nm on MgO. The CEMS spectra are observed at 15–300 K with a gas-filled proportional counter which was developed in our laboratory. The hyperfine fields in the surface layer and in the core of the particles are separated. The diameter and magnetic anisotropy energy constant are 3.7 nm and 0.87 × 10 5 J/m 3 , and 3.5 nm and 2.4 × 10 5 J/m 3 , respectively, for small particles on aluminum and MgO. The large difference in the anisotropy constants of small particles on aluminum and MgO is attributed to the enhanced surface anisotropy, which may be caused by diffusion of magnesium ions into the lattice of iron oxide. The superparamagnetic blocking temperatures of these particles are 71 and 94 K, respectively.

Depth selectivity at low temperatures with a proportional counter

Abstract Depth-selective conversion electron Mossbauer measurements were demonstrated at 15 and 77 K with a proportional counter. In spite of a comparatively poor energy resolution of the counter at low temperatures, a depth selectivity similar to that at room temperature was obtained.

CEMS at low temperature with a gas mixture of helium and neon

Abstract Operational technique of a gas-filled proportional counter for CEMS measurements was improved at temperatures between 20 and 45 K. The best CEMS spectrum was obtained when 0.2–0.5 atm neon and helium is filled in the counter under the conditions that the total pressure of neon and helium is 1 atm.

Formation of iron fine particles in a crystal lattice by the computer simulation

The growing up of the fine particles in a sapphire crystal was simulated with a computer and the expected Mössbauer spectra were calculated by considering the influence of the nearest neighbors and next-nearest neighbors to the magnetic hyperfine field of the iron atoms. The simulated spectra were compared with the Mössbauer spectra observed with a Fe-implanted sapphire and the agreement between them was satisfactory on the whole. It is also revealed that an iron atom implanted into a sapphire crystal may interact, before coming to rest, with the iron fine particles situated within 2–3 nm in the crystal.

LOW TEMPERATURE CEMS OF CORROSION PRODUCTS BY SULFURIC ACID WATER

Conversion electron Mössbauer spectroscopy (CEMS) was used to study the corrosion products by sulfuric acid water. The acid water was put on the iron foil and evaporated under the atmosphere of several oxygen ratios in nitrogen-oxygen gas mixture in order to investigate the influence of oxygen contents on the corrosion products. The hyperfine fields of the observed sextets at 15 K suggest that the corrosion products consist of α-FeOOH, γ-FeOOH and γ-Fe2O3. The amount of γ-FeOOH becomes larger as the oxygen concentration increases. It is also found that the amount of γ-Fe2O3 becomes the largest at 1.4 % of the oxygen concentration.

Chemical mixing at “Al on Fe” and “Fe on Al” interfaces

The chemical mixing at the “Al on Fe” and “Fe on Al” interfaces was studied by molecular dynamics simulations of the layer growth and by 57Fe Mossbauer spectroscopy. The concentration distribution along the layer growth direction was calculated for different crystallographic orientations, and atomically sharp “Al on Fe” interfaces were found when Al grows over (001) and (110) oriented Fe layers. The Al/Fe(111) interface is also narrow as compared to the intermixing found at the “Fe on Al” interfaces for any orientation. Conversion electron Mossbauer measurements of trilayers—Al/57Fe/Al and Al/57Fe/Ag grown simultaneously over Si(111) substrate by vacuum evaporation—support the results of the molecular dynamics calculations.

The clay wall of an ancient iron smelting furnace studied by Mössbauer spectroscopy

For an investigation of the ancient iron manufacturing technique, a modern simulation experiment was carried out. The smelting furnaces were built with clay. Charcoal and raw materials were installed from the top of the furnace. Magnetite was used as the raw material. In the furnace, iron oxide was reduced to metallic iron. The reduction reaction was mainly controlled by temperature and oxygen fugacity in the furnace. In order to investigate the possibility for the estimation of these parameters, 57Fe Mössbauer spectra were recorded of the furnace wall at room temperature.