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Co1 + x Si x Fe2 − 2x O4 ferrite system has been studied to estimate the influence of Si and Co substitutions together on the magnetic and magnetostrictive properties. The samples were prepared by standard double sintering ceramic technique. X-ray diffraction patterns of the study confirm spinel crystal structures. Hysteresis and magnetostriction measurements were made on all the samples at room temperature. Mossbauer spectra were also made both at 300 K and at 4 K under the applied field of 5 T in the direction of gamma ray. Nominal decreases in Curie temperature and saturation magnetization were observed. The strain derivative, which relates to stress sensitivity, is observed to increase from 1.13 × 10 − 9 to 2.51 × 10 − 9 A − 1 m for x = 0.2 silicon concentration. The variations are explained on the basis of the strength of the exchange interactions between cations, and anisotropy modifications induced by migration of cobalt ions. The results demonstrate the possibility of controlling the magnetic and magnetomechanical properties through Co and Si substitutions.

Silicon substituted cobalt ferrites have been investigated for improved performance as stress sensing materials. A series of samples with the formulae CoSi x Fe2 − x O4 were prepared using conventional powder ceramic technique. X-ray diffraction patterns were taken to examine spinel crystal structures and energy dispersive spectrometry was done to confirm Si segregations at the grain boundaries. Magnetic and magneto-strictive measurements were carried out to evaluate the material performance. Mossbauer spectra were taken on selective samples to understand the cationic distribution responsible for the modification of properties. The variations are explained on the basis of the strength of the exchange interactions between cations, and anisotropy contributions of cobalt ions. The results demonstrate the possibility of controlling magnetic and magneto-mechanical properties such as Curie temperature and strain derivative through Co and Si substitutions.

Mossbauer effect studies on some natural magnetite ore samples from India are reported for the first time. Using the Mossbauer spectroscopy data, the magnetites of sedimentary origin are differentiated from those of igneous origin. The igneous magnetites are found to have a nearly stoichiometric composition. A titanium enrichment in these samples was also evidenced. The magnetites of sedimentary origin, however, have almost fully oxidized to haematite.

The nuclear quadrupole interaction at the100Rh probe nucleus in a Be host is measured from 4.2–968 K using time-differential perturbed γ-γ angular correlations of the 84–75 keV cascade in the de-excitation of100Rh. The sources were prepared by recoilimplanting the parent100Pd activity produced in a heavy-ion reaction. The temperature variation of the electric field gradient can nicely be fitted by aT3/2 law.

The large recoil energies offered by the heavy ion nuclear reactions were used to implant the100Pd(3.6 d) activity into different host matrices. The sources thus prepared were found to have good strengths and small background activities. The yields were quite high ∼3μCi/1μAh beam current of12C4+ and the efficiencies of implantation were in the range 60–70%. The difference in the recoil energies of the target and the catcher may be used to reduce activities due to unwanted nuclear reactions in the catcher foil. Using this method, we were able to prepare excellent sources of100Pd in Be, Mg, Ti, Zr and Re hosts. The quality of these sources is comparable to that of the100PdBe ion implanted sources for which data are available in the literature.

Optogalvanic Spectroscopy (OGS) is finding wide ranging applications in atomic structure studies, laser wavelength calibration, intensity and frequency stabilization of lasers and analytical chemistry. Sputtered atoms produced in a hollow cathode lamp by the bombardment of a rare gas discharge is a convenient source for optogalvanic spectroscopy work. Here, we discuss the sputtered ion/atom optogalvanic spectroscopy applications to low resolution atomic spectroscopy, laser wavelength calibration, studies of radioactive samples available in limited quantities, studies of atoms in highly excited states and Rydberg atoms and high resolution laser spectroscopy. For the sake of completeness, we list other applications of OGS without going into details.

Mossbauer studies of a large number of glass samples prepared with alkali oxides in the region of glass formation are reported. Some representative samples are studied in the temperature range 85–500 K. The following glass systems are studied. Room-temperature isomer shift values decrease gradually with the addition of alkali oxide and the values fall sharply for alkali content higher than 22 mol%. We conclude that iron is in the ferric state and that the oxygen polyhedra of iron changes from octahedral to tetrahedral. The structural change results from the fact that the alkali introduces an extra non-bridging oxygen ion. The size of the alkali cation introduced into the glass has considerable influence on the isomer shift values of iron. In fact, the polarizing power decreases in the order LiNaK, hence the s-character of the FeO bond increases in the order LiNaK. Addition of Al2O3 has no effect on the isomer shift values of iron, showing that aluminium ions occupy network-forming positions. For some representative samples the second-order Doppler effect was studied as a function of temperature in the range 85–500 K. The thermal red shifts due to second-order Doppler effect are used to estimate the local specific heats of ferric ion in the glass system. The quadrupole splitting has weak temperature dependence, showing that Fe3+ is in a high-spin state.

The nuclear quadrupole interaction at57Fe nuclei in hcp α-zirconium metal is measured in the temperature range 4.2 to 560 K using Mossbauer spectroscopy of57Fe. The quadrupole splitting at room temperature is measured to be 0.660(8) mm/sec which corresponds to an electric field gradient of |eq|=3.17×1017 V/cm2 at the57Fe nucleus in a α-Zr host. As has been observed in many other systems, the results show significant electronic contributions. The temperature variation of the quadrupole interaction is much stronger than is expected from the lattice contributions and is found to follow theT 3/2 dependence approximately.57FeZr does not follow the universal correlation betweeneq ion andeq el observed in most of the normal metal hosts but follows the trends recently observed by Krusch and Forker for the transition metal hosts. Our results are compared with the predictions of the conduction electron charge shift model recently proposed by Bodenstedt and Perscheid.

High resolution time differential angular correlation, now achievable at low cost by the fast and efficient BaF2 detectors, will be introduced from some examples recently worked out. The results obtained manifest a new impetus for this technique in its extended application to particular problems in nuclear solid state research.

The electric field gradients (EFGs) at different probe nuclei in Ti and Re hosts are compared with the predictions of the conduction electron charge shift model. It is found that this model is successful in predicting the sign and, to a zero-order approximation, the magnitude of the EFG when the localized d-contributions are small and the universal correlation is obeyed.

All data available in the literature for the impurity hyperfine fields in Fe, Co, Ni and Gd matrices are collected and tabulated. The literature search was carried out for all references listed in Physics Abstracts on papers published till the end of December 1978. The present work is an extension of similar earlier compilations [1–6]. The data are arranged in ten columns as explained below

Time differential perturbed angular correlation experiments were carried out using111Cd probe nuclei to measure the change in conduction electron polarization at different lattice sites due to scattering around an impurity atom.

We demonstrate an application of PAC to the study of magnetic ordering in random alloys. Using111Cd as a probe the spin-glass freezing inAuFe-alloys of different concentrations could be observed. In the Au82Fe18 alloy no indication of ferromagnetism above the freezing temperature was found, due to the fact that the111In probe nuclei are located in a Au rich environment.