Hyperfine Interaction of111Cd Research Articles

Growth of Ga2O3 by furnace oxidation of GaN studied by perturbed angular correlations

Ga2O3 is a promising material for use in “solar-blind” UV-detectors which can be produced efficiently by oxidation of GaN. In this study we focus on the evolution of the oxide layer when GaN is heated in air. The experimental method applied is the perturbed angular correlation (PAC) spectroscopy of γ-rays emitted by radioactive nuclides, here 111Cd and 181Ta, whose parent nuclei are ion implanted into films of GaN grown on sapphire. As the emission pattern for nuclei in GaN is clearly distinct from that of nuclei in Ga2O3, the fraction of probe nuclei in the oxide layer can be directly measured and allows to follow the time dependent growth of the oxide on a scale of less than 100 nm. Additional measurements were carried out with the oxidized sample held at fixed temperatures in the temperature range from 19 K to 973 K showing transitions between the hyperfine interactions of 111Cd in the oxide matrix both at high and low temperatures. A model for these transitions is proposed.

111Cd PAC Study of Gd–Ni Intermetallic Compounds

This paper presents a perturbed angular correlation study of the magnetic and electric hyperfine interactions of 111Cd on Gd sites of the Gd-Ni intermetallic compounds GdNi, GdNi2, GdNi3, Gd2Ni7, GdNi5 and Gd2Ni17.

Hyperfine interaction of 111Cd in Fe–Sn compounds

Iron–tin compounds of different stoichiometries were studied by the perturbed angular correlation method. The hyperfine interaction parameters and their temperature dependence for 111Cd probes substituting for tin in FeSn 2, FeSn and Fe 3Sn 2 crystal lattices were determined.

Influence of the temperature and the ionisation potential on the hyperfine interaction of 111 Cd ions in gaseous radioactive indium-halides

The hyperfine interaction (HFI) of 111Cd in different indium‐halides was studied by perturbed angular correlation (PAC). The 111Cd ion arises from a 111In by electron capture decay (EC) and joined Auger cascade. Coulomb fragmentation of the indium‐halide molecule produces the free excited 111Cd ion. The nucleus decays via a γ–γ‐cascade which is perturbed by the HFI. Collisions of the 111Cd ion with indium‐halide molecules can strongly change the perturbation. The perturbation was measured by the attenuation coefficient G22(∞) and G22(t). The molecular densities varied between 1014 and 1020 cm−3. The present article shows the temperature dependence of the indium(III)‐halides and a fit for an empirical basic approach. The investigation of the InBr shows the independence of the attenuation coefficient from the temperature by indium(I)‐halides in contrast to the dependence of the indium(III)‐halides.

Hyperfine Interactions of111Cd in Some Rare Earth Laves Phases RT2 (T = Mn, Fe)

Radioactive 111 In was introduced into the Laves phases YMn 2 , GdFe 2 and YbFe 2 synthesized under pressure of 8 GPa, and the hyperfine interaction of the daughter 111 Cd was measured by the perturbed angular correlation method. In the obtained hexagonal (C14) phase YMn 2 111 In is substituted for Mn, predominantly at h-sites, experiencing there an electric quadrupole interaction with ν Q = 32.0(5) MHz and η = 0.51(5) at 300 K. In GdFe 2 and YbFe 2 (cubic C15) most of the 111 In-1 1 Cd probes (80%) substituted mainly for the rare earth atoms and experienced a magnetic hyperfine field |B hf | = 2.92(4) T and 3.32(7) T, respectively, at 300 K. The results are discussed together with the published data for the normal cubic YMn 2 , and for LuFe 2 and ZrFe 2 .

Studies of the hyperfine interaction of111Cd in gaseous InCl and InCl3 systems

Using the perturbed γ-γ angular correlation at excited111Cd-ions from the decay of111In, the time-integral attenuation coefficientG 22(∞) was measured in gaseous InCl and InCl3 surroundings. The perturbation depends as well on the character and the density of the surrounding gas, as on the angular momentum of the electronic shell of the Cd-ion.G 22(∞) varied between 0.012 and 0.828, while the molecule densities varied between 2×1014 and 2×1020 molecules/cm3. For high densities it is to be noted, that the perturbation vanishes much faster for the InCl systems. Using a stochastic model, it is possible to calculate the mean hyperfine frequency Ω0, and to estimate cross-sections for molecule-ion collisions at thermal energies.

Hyperfine interaction of111Cd in In-Pd intermetallic compounds

Perturbed γ-γ angular correlation (PAC) spectroscopy was applied to study the hyperfine parameters for111In probes in In-Pd intermetallic compounds. The PAC spectra measured in In3Pd, In3Pd2 and InPd2 compounds reflect the number, population and symmetry of nonequivalent indium probe sites predicted by the crystallographic data. The temperature dependence of the observed electric field gradients was measured in the temperature range 80–873 K.

The magnetic hyperfine interaction of111Cd in the spinels Fe3O4 and Co3O4

The perturbed angular correlation (PAC) method was applied to study the temperature dependence of the magnetic hyperfine fields in111In-doped polycrystalline Fe3O4 and Co3O4. The critical behaviour near the magnetic phase transitions has been investigated. The changes occuring near the Vervey transition in Fe3O4 and the path of the supertransferred magnetic fied in Co3O4 are discussed. The results are compared with results obtained from Mossbauer spectroscopy.

Pressure and temperature dependence of the electric field gradient (EFG) in CdS

Using the time differential perturbed angular correlation technique (TDPAC), the electric hyperfine interaction of111Cd in the II-VI-semiconductor CdS was investigated. The results of the temperature and pressure dependence of the electric field gradient (EFG) are discussed. The binding energyEb for111In at a Cd lattice site and a Cd vacancy (111InCd−VCd−pair) could be estimated to 340 meV±80 meV by means of an Arrhenius-Plot. The disappearance of the 79 MHz and 73 MHz frequencies under a pressure of about 30 kbar could be due to their vacancy character or to the beginning of the phase transition to rocksalt structure.

Perturbed angular correlation experiments on111In in oxidized AgCd alloy

The hyperfine interaction of111Cd probes in preoxidized and α-irradiated Ag0.94Cd0.06 alloy has been investigated by PAC measurements and compared with the results for pure Ag. Several probe atom sites were distinguished and characterized by their hyperfine parameters and temperature evolution. The different behavior of In-oxygen and In-oxygen-vacancy complexes in AgCd and Ag was found and discussed. A considerable influence of the irradiation temperature and sample thickness on the different In-oxygen-vacancy complexes formation was evidenced. The parameters of111Cd quadrupole interaction measured during isochronal annealing studies in preoxidized and deuteron irradiated AgCd were very similar to the ones observed after α-irradiation.

Preferential site occupation of indium in β-Ga2O3

The hyperfine interactions of111Cd in gallium oxide doped with111In have been studied as a function of temperature (300–1323 K) by means of the time differential perturbed angular correlation technique. The observed hyperfine interactions are assigned to the the β — form of gallium oxide. X-ray diffraction analysis support this conclusion. It is found that indium replace gallium at only one site of both possible sites in the monoclinic β — structure. This site is probably the sixfold corrdinated one. On the other hand, a time dependent interaction is detected at temperatures below 800 K.

Hyperfine interactions of111Cd impurities in Cr2O3

The electric and (antiferro-)magnetic hyperfine interaction of111Cd in α-Cr2O3 after111In implantation was studied via PAC. Two fractions with axially symmetric electric field gradients were observed having antishielding factors of Vzz/Vzzpc=79(12) and 106(16), respectively. From the line broadening of the Fourier components of the first fraction its supertransferred magnetic field was estimated as Bloc (20 K)≤0.41 T, about two orders of magnitude smaller than for substitutional111Cd in NiO and CoO.

Hyperfine interactions of111Cd in ion-implanted face centered cubic cobalt

The magnetic-dipole and electric-quadrupole hyperfine interactions of111Cd probes in fcc cobalt after implantation of radioactive111In+ ions have been investigated by PAC measurements with fast BaF2 detectors. Six different sites of the probe atoms could be distinguished and characterized by their hyperfine parameters and annealing behaviour. Besides the substitutional site, three sites are assigned to In-vacancy complexes which are formed athermally in the implantation process or by thermally-activated trapping of lattice defects in annealing stage III. The remaining two sites are attributed to In located in stacking faults or hcp regions of the host. Systematic trends of impurity hyperfine fields in defect sites become evident from a comparison with other impurity-host combinations. The temperature dependence of the magnetic hyperfine fields has been measured between 20 K and 390 K. Large differences found for the various sites are discussed.

Hyperfine interaction of111Cd in antiferromagnetic cobalt oxide

The temperature dependence of the hyperfine field of substitutional111Cd in antiferromagnetic CoO has been measured by means of the perturbed angular correlation technique. The Larmor frequency ωL is found to obey a power law ωL(t=ω0 t β) up tot max=0.4 wheret=1−T/T N is the reduced temperature withT N=291.2(3) K and β=0.393 (5) the critical exponent. The results are discussed and compared with PAC experiments on111Cd in NiO and Ni and with results obtained by other methods.

The effect of temperature and concentration on the electric field gradient in binary indium alloys

The concentration and temperature dependence of the quadrupole hyperfine interaction of111Cd in InTl (hcp),InPb (fct),InTl (fct) andInCd (fct and fcc) alloys were studied using the perturbed angular correlation technique. The change in the observed quadrupole interaction frequency with concentration can be described by a linear dependence on the axial ratioc/a in all cases. In the alloys with identical crystal structures the strength of thec/a dependence is independent of the solute, in contrast to the strength of the concentration dependence. In all cases where no phase transition occurs, the change in the electric field gradient with temperature follows the empirical relationVzz(T)=Vzz(0) · (1−B·T3/2), where the coefficientB depends on the lattice structure, on the solute-solvent combination and on the concentration. The phase transitions ofInCd alloys at 293 K could clearly be seen as discontinuities in the temperature curves. A similar series of discontinuities observed around 116 K suggests the existence of a cubic low temperature phase.

Temperature dependence of the electric field gradient in noncubic metals

The quadrupole hyperfine interaction of111Cd in Cd, In, Sn, and of67Zn,69Ge in Zn was measured with high accuracy using TDPAC and TDPAD methods; in addition the systems117In in Cd and In, and113Sn in Cd were investigated. The temperature dependence of the electric field gradienteq(T) can be reproduced by the simple relationeq(T)/eq(0)=1—B⋅T 3/2 over a range of temperatures from a few K up to the melting point. A comparison with other experiments was carried out to test the universality of this empirical relation. In particular, high precision NQR experiments on Ga, In and Sb strongly support this relation. It is discussed whether lattice vibrations can explain the observed temperature variation or whether the experimental data indicate the need for a new description. Some new ideas suggesting a basically different model are given.