Frederick W. Oliver

Transmission Mössbauer spectroscopy on pulsed-laser-deposited thick Fe and Ni–Zn ferrite films

Mossbauer spectroscopy with 57Fe is used to characterize pulsed-laser-deposited (PLD) Ni0.6Zny–Fe2O4 films is demonstrated. Mossbauer spectra were recorded as a function of film thickness (3–16 μm) for films deposited in background O2 pressures of 50 and 200 mTorr, and for a zinc concentration of y=0.72. A spectrum was also recorded for y=0.4 deposited in a background pressure of 200 mTorr. The site occupancy was determined for the tetrahedral (A) and octahedral (B) sites. Results obtained here show that the effect of increasing the Zn is to shift Fe(tet) to Fe(oct). When compared with previous Mossbauer measurements on the bulk NiZn ferrites, the ferrite films give spectra of similar quality with no visible evidence of clustering or multiple phases present. The same linewidth was found for a PLD processed Fe film and a Mossbauer standard 70-μm-thick α-Fe enriched foil. The Fe film had a magnetic hyperfine field of 334 kOe and no evidence of the presence of any iron oxides. Good spectra may be obtained by...

Mössbauer studies on LaNi4.7Sn0.3 and its hydride

Mossbauer measurements were made on LaNi4.7Sn0.3 at room and liquid nitrogen temperatures. Experimental data yielded a singlet at room temperature and a doublet at liquid nitrogen temperature. Spectra of the hydrided sample yielded a doublet at liquid nitrogen temperature with an increase in the quadrupole splitting compared to the unhydrided spectra, but no change in the isomer shift. These data indicate that there is no significant interaction between the tin and the hydrogen. The magnetic character remained the same down to liquid nitrogen temperature as evidenced by the Mossbauer data. X‐ray diffraction measurements on the hydride showed an expanded lattice with the same structure as found for the unhydrided sample. A decrease in particle size was observed upon hydriding.

Study of mechanical alloying of Sm and Fe

Mechanical alloying of Sm and Fe with the composition of SmFe3 was studied using x-ray-diffraction (XRD), Mossbauer, and magnetization measurements. Data taken as a function of milling time for up to 20 h show significant changes occurring during ball milling. The XRD studies show that the initial crystalline Bragg reflections changed to a broad maximum, which is attributed to the formation of an amorphous phase. The initial six-line pattern in the Mossbauer spectrum, characteristic of magnetic ordering, changed to a broad singlet, characteristic of a nonmagnetic material. Magnetization measurements revealed that the coercive field was at its maximum after 5 h of milling and decreased sharply as the milling time increased. The remanent magnetization was at its maximum between 5 and 10 h of milling. The final product of the ball milling, which exhibited the characteristics of an amorphous paramagnetic material in its XRD and Mossbauer spectrum, was studied after heat treatment. The XRD and the Mossbauer sp...

Mössbauer and magnetic‐susceptibility studies on MmNi4.15Fe0.85 and its hydride

Results are reported on MmNi5−xFex (x=0.85) (Mm=mischmetal) and its hydride from magnetic susceptibility (χ), Mossbauer, and scanning‐electron‐microscopy studies. The magnitude of χ, the shape of the χ‐vs‐T curve (50–300 K), and the magnitude of Tc (≂200 K) are all close to the values reported for LaNi4Fe. The magnetic properties are significantly changed by the hydriding process. χ (at 100 Oe) above Tc is increased by 100%, whereas at 77 K, χ is lowered by 25%, although Tc is unaffected. The Mossbauer spectra above Tc yield a paramagnetic doublet (isomer shift −0.13±0.01 mm s−1); however, as the temperature decreases, the doublet disappears at 125 K. Hydriding causes only a very small change in the isomer shift.

Paramagnetic Europium Salen Complex and Sickle‐Cell Anemia

A new europium salen complex, Eu(salen)2NH4, was synthesized, and its composition was confirmed by chemical analysis and infrared spectroscopy. Further characterization was carried out by 151 Eu Mossbauer spectroscopy and magnetic susceptibility measurements. Mossbauer spectroscopic measurements were made at varying temperatures between 9 K and room temperature and a value of Debye temperature of 133 ±5 K was computed. Both Mossbauer and magnetic susceptibility measurements confirmed the paramagnetic behavior of this complex and the trivalent state of the europium ion. In view of the fact that the “odd” paramagnetic molecule NO has been shown to reverse sickling of red blood cells in sickle cell anemia, the interaction between the paramagnetic europium salen complex and sickle cells was examined after incubation with this europium complex and shown to have similar effects.

57Fe Mössbauer Spectroscopy in Coal with Different Caloric Values

The environmental concern associated with mining and burning of coal has long been discussed in the literature. The present study deals with the four different ranks of coal with varying calorific values (CV) aiming to determine if these values are influenced by the sulfur content and/or the forms of iron-sulfur minerals associated with these types of coal. It has been established that Mossbauer spectroscopy is undoubtedly the best analytical tool for discerning iron minerals. The four different types of coal had CVs ranging from 32,403 to 16,000 kJ/kg and sulfur concentrations ranging from 0.25 to 2.5%. There was no direct correlation between the CV and the percentage of pyrites and ferrous sulphate. However, in general, as the CV increases, the percentage of sulfur increases.

Magnetic properties of bulk Eu2/3Ca1/3MnO3

The magnetic and structural properties of the bulk manganite Eu2/3Ca1/3MnO3 are characterized using Mossbauer spectroscopy, magnetization measurements, x-ray diffraction, and resistivity measurements. Here it is demonstrated that one can investigate the magnetic properties of manganites using Mossbauer spectroscopy by doping with europium at the rare earth site and using rays from Eu151 as a probe. Mossbauer measurements were performed at several temperatures between 15 and 293 K using a 151Eu source. The spectrum at room temperature is a single line demonstrating paramagnetism with an isomer shift of 0.60±0.02 mm/s. Measurements at room temperature show the Eu to be trivalent and single phase with a linewidth of 2.933±0.004 mm/s, which is comparable to that found for the Mossbauer standard EuF3. Measurements below 100 K show a much broader linewidth which at 15 K is more than twice that found at 293 K and is associated with a magnetic phase transition. Magnetization as a function of magnetic field measur...

Mössbauer studies on Fe–W alloys synthesized by mechanical alloying (abstract)

Mechanical alloying in Fe–W alloys has been studied using Mossbauer, and magnetic susceptibility measurements. Mossbauer spectra show that during initial milling a six line pattern characteristic of magnetic ordering is present and with continued milling the spectrum transforms into a broad singlet, which is characteristic of nonmagnetic material. Experimental data show that after 7 h of ball milling, the iron component homogenizes and becomes amorphous. The Mossbauer results are qualitatively consistent with earlier Mossbauer reports on Fe–V powder,1,2 and more recent measurements on Fe–W using other characterization methods.3 Changes in the Mossbauer results agreed with the associated magnetic susceptibility measurements and there was a significant decrease in the magnetic susceptibility for milling times between 2 and 25 h. A discussion of the experimental measurements will be reported and compared with other experimental investigations on mechanical alloys.

Mössbauer and magnetic studies of Eu porphyrins (abstract)

We report the first measurements on porphyrin compounds using Eu as the Mossbauer nuclide. There have been many Mossbauer studies on iron porphyrins1,2 and a few on tin.3 We have successfully prepared and made Mossbauer and magnetic susceptibility measurements on four Eu based porphyrin compounds to elucidate the relationship between magnetic properties and structure. Absorption spectra using the 21.6 keV gamma ray of 151Eu were obtained at room temperature and 80 K and yielded very broad singlets with room temperature isomer shift values between 0.20±0.02 mm/s and 0.90±0.02 mm/s with respect to EuF3. Experimental results show the Eu ion to be in the trivalent oxidation state. A discussion of the electronic properties and structure will be reported and compared with previous results found on iron and tin based porphyrins.

151Eu Mössbauer study of the high‐Tc superconductor Bi2Ca0.5Eu0.5Sr2Cu2Ox (abstract)

Isomer shift measurements show the Eu to be trivalent and nonmagnetic with no apparent anomaly between measurements made above and below the transition temperature (Tc=87 K). The value of the isomer shift at room temperature (0.69±0.02 mm/s) falls within the values observed by previous researchers on other types of Eu‐based high‐Tc superconductors. A discussion on the isomer shift and f factor as a function of temperature will be reported and compared with previous results found in Eu‐based high‐Tc superconductors.1–3