Electric quadrupole interaction at 111Cd and 119Sn in isostructural NiIn and CoSn compounds

The perturbed angular correlation technique and Mössbauer spectroscopy were applied to study the electric field gradient on ¹¹¹Cd and ¹¹⁹Sn probe atoms in isostructural NiIn and CoSn compounds. The ¹¹¹Cd PAC measurements performed in the temperature range 80--1100 K demonstrated the existence of two axially symmetric EFG's in each of the investigated compounds, related to the 2(d) and 1(a) probe sites in the B35 structure. A 1(a)-site preference for Cd probes in CoSn compound was observed. The temperature dependence of the quadrupole frequencies for ¹¹¹Cd in both compounds, interpreted in terms of the empirical model proposed by Christiansen et al.[1], follows a T^3/2 relation with different slope parameters for each of the observed frequencies. These results are combined with the data from the Mössbauer experiment. The ¹¹⁹Sn Mössbauer spectra taken at liquid nitrogen and at room temperatures showed two quadrupole split doublets with the intensity ratio 2:1 for CoSn and 8:1 for NiIn_0.99Sn_0.01sample, giving an evidence of 2(d)-site preference for tin atoms in NiIn. The EFG values measured on ¹¹⁹Sn are 2.5 to 4 times larger than those on ¹¹¹Cd nuclei, while the ratio of the respective Sternheimer antishielding factors is equal to 0.77. Within the limits of errors no differences were observed in the magnitude and temperature dependence of Debye--Waller factors for 2(d) and 1(a) ¹¹⁹Sn positions in CoSn and NiIn lattices.     

111In(111Cd) quadrupole interaction in the chalcogenide spinel CdCr2Se4

The¹¹¹Cd quadrupole coupling in the spinel CdCr₂Se₄ is investigated by TDPAC after different sample treatments. The experiments are consistent with Se vacancies causing the non-cubic probe environments and with the assumption that the majority of the¹¹¹In atoms are positioned at A-sites.     

The electric quadrupole interaction of 111Cd in ZrZn2 and Zn in the samples prepared at 8 GPa

The perturbed angular correlation (PAC) measurements with the ¹¹¹In-¹¹¹Cd nuclear probe embedded into the lattice of the cubic (C15) Laves compound ZrZn₂ showed that ¹¹¹Cd nuclei experienced an axially symmetric electric quadrupole interaction with a frequency ν _Q  = 132.4 MHz at room temperature. The samples were synthesized and doped with the probe at a pressure 8 GPa. The temperature dependence of ν _Q was shown to be linear: ν _Q (T) = 147(1 − 0.033 T) MHz. Since the value of ν _Q is very close to that known for ¹¹¹Cd in the lattice of Zn, we have checked if it could be assigned to residual Zn metal in the sample. For the Zn sample melted and doped with ¹¹¹In at 8 GPa we have obtained ν _Q  = 117.3 MHz at 300 K and 127 MHz at 80 K – both values considerably lower than that for ¹¹¹In doped Zn samples prepared at an ambient pressure. These data, and the fact that ν _Q (T) in Zn is known to follow the T ^3/2 law, allow to attribute the ν _Q value quoted above to ¹¹¹Cd nuclei at the substitutional sites with tetrahedral symmetry in the Zn sublattice of ZrZn₂.     

Hyperfine interaction at111Cd in manganese

The hyperfine interaction is studied in two different crystal lografic forms of Mn. In the -Mn no magnetic, but a distinct electric quadrupole interaction is found. Effects of heat treatment are discussed. For the -Mn two magnetic field sites are found. Their temperature dependence and dependence on the In concentration are discussed.     

TDPAC investigations of the111Cd quadrupole interaction in ternary chalcopyrite semiconductors

The quadrupole interaction at room temperature of¹¹¹Cd in CdSiP₂, CdGeP₂, and CdSnP₂ is investigated by^111mCd-TDPAC. The results are compared with those of former¹¹¹In(¹¹¹Cd) measurements. We observed axially symmetric quadrupole interactions with identical quadrupole coupling constants provided that radiation damage was annealed. This proves that also In probes are positioned at Cd-sites (A-sites) in these ternary compounds.     

Temperature dependence study of the quadrupole interaction of111Cd in tellurium

A quadrupole interaction corresponding to an interstitial site of axial symmetry has been observed for the 247 keV state of¹¹¹Cd in tellurium. A possible site is suggested, but little or no temperature dependence has been observed.Supported in part by the US energy Research and Development Administration.     

Temperature dependence study of the quadrupole interaction of111Cd in antimony

A power law dependence has been observed for the temperature dependence of the quadrupole interaction of the 247 keV state of¹¹¹Cd in antimony, which is similar to that observed for¹²¹Sb and¹²³Sb in antimony.Supported in part by the US Energy Research and Development Administration.     

TDPAC measurement of quadrupole interaction at111Cd in the nearly heavy fermion system USn2.9

Quadrupole interaction at¹¹¹Cd probe has been studied in the nearly heavy fermion system USn_3– using the TDPAC method. We observe a large quadrupole interaction frequency withv _Q =89.9(10) MHz at 300 K which is much higher than the earlier reported result. The observed frequency shows a linear temperature dependence in the range 25–300 K.     

The nuclear quadrupole interaction at 111Cd and 181Ta sites in anatase and rutile TiO2: A TDPAC study

The nuclear quadrupole interaction of the I=5/2 state of the nuclear probes ¹¹¹Cd and ¹⁸¹Ta in the anatase and rutile polymorphs of bulk TiO₂ was studied using the time differential perturbed angular correlation (TDPAC) method. The fast–slow coincidence setup is based on CAMAC electronics. For anatase, the asymmetry parameter of the electric field gradient was η=0.22(1) and a quadrupole interaction frequency of ω_Q=44.01(3) Mrad/s was obtained for ¹⁸¹Ta. For rutile, the respective values are η=0.56(1) and ω_Q=130.07(9) Mrad/s. The values for rutile match closely with the literature values. In case of the ¹¹¹Cd probe produced from the beta decay of ¹¹¹Ag, the quadrupole interaction frequency for anatase was negligibly small as indicated by an unperturbed angular correlation in anatase. On the other hand for rutile the quadrupole frequency is ω_Q=61.74(2) Mrad/s and the asymmetry parameter η=0.23(1) for the ¹¹¹Cd probe. The results are interpreted in terms of the surrounding atom positions in the lattice and the charge state of the probe nucleus.     

Quadrupole interaction at111Cd in rare-earth intermetallics

Quadrupole interactions at¹¹¹Cd in various rare-earth intermetallics have been investigated. The enhancement in the efg due to the electronic configurations is found to be small in contrast to pure metals.The authors thank K. Raghunathan for helpful discussions.     

Quadrupole interaction at111Cd nuclein in single-crystalline thallium

The quadrupole interaction of¹¹¹Cd nuclei in a single crystal of hexagonal thallium has been investigated for different geometries and sample temperatures employing the perturbed - angular correlation technique. The observed variation of the electric field gradient with temperature is attributed to local modes of thermal vibrations of the Cd impurities. An analytical relationship has been derived from lattice-dynamical models, expressing the temperature dependence in terms of impurity-host mass ratios and local force-constants.     

Nuclear quadrupole interaction of111Cd on type-1 Cu-sites in blue copper proteins

The nuclear quadrupole interaction (NQI) of¹¹¹Cd substituted for Cu(II) on type-1 sites in blue copper proteins is characterized by high values of ₀ in the region of 300 Mrad/s, close to that for the catalytic zinc site in alcohol dehydrogenase. Type-1 Cu has usually two sulfur ligands and two nitrogen ligands and in some cases an oxygen ligand in either a distorted tetrahedral geometry or in a trigonal bipyramidal geometry. The near tetrahedral arrangement together with the ligand sphere containing the same number of sulfur ligands explains the value of ₀ in the blue copper proteins. The present work determined the partial NQI for methionine using the known structure of azurin. This value was then used in the angular overlap model to calculate the NQI for ascorbate oxidase the structure of which is also known and gave good agreement with experiment. NQI data for laccase and stellacyanin the structures of which are unknown, are also given.On leave from Technische Universität München, Germany.     

Linear temperature dependence of the electric quadrupole interaction of111Cd impurities in holmium

The electric quadrupole interaction of¹¹¹Cd impurities in metallic holmium has been investigated between 140 K and 655 K by time differential perturbed angular correlation measurements. The quadrupole frequency decreases with increasing temperature. This decrease is a linear function of temperature, in contrast to theT ^3/2 dependence usually observed in non-cubic metals. Possible reasons for the deviation from theT ^3/2 relation are discussed.     

55Mn nuclear magnetic resonance study of high-pressure synthesized hexagonal DyMn2, TbMn2 and GdMn2

The ground state magnetic properties of high-pressure synthesized Laves phase compounds with the hexagonal C14 structure, DyMn₂, TbMn₂ and GdMn₂, were investigated by ⁵⁵Mn nuclear magnetic resonance technique and compared with those of the equilibrium phases with the cubic C15 structure. We observed two different signals in zero field for DyMn₂, which are just the same as those for the C15 phase, indicating the coexistence of magnetic and non-magnetic manganese sites. For TbMn₂, a zero-field spectrum with two peaks was observed in the frequency range below 80 MHz, suggesting that the manganese moment becomes unstable and that manganese atoms are partially non-magnetic, which is in contrast to large and stable magnetic moments in the C15 phase. For GdMn₂, a broad zero-field spectrum was observed just in the same frequency range as that of the C15 phase, indicating that all manganese atoms have stable large moments.     

Exchange interaction and magnetocrystalline anisotropy in GdMn2Ge2

Tetragonal GdMn₂Ge₂ is a ferrimagnet at low temperatures and changes to an antiferromagnet undergoing a first-order transition at 95 K. The temperature dependence of the magnetization has been analyzed in terms of the molecular-field approximation with interactions between Gd-Gd, Gd-Mn and Mn-Mn atoms. The Gd-Mn interaction is antiferromagnetic, and this permits the appearance of the ferrimagnetic structure at low temperatures. The uniaxial anisotropy (the easy axis of magnetization is the c-axis for both Gd and Mn moments) plays an important role in the first-order ferrimagnetic to antiferromagnetic transition.