The electric fieldgradient of the transition element impurities57Fe,99Ru,197Au in scandium and193Ir in beryllium

The electric fieldgradient of the transition element impurities⁵⁷Fe,⁹⁹Ru,¹⁹⁷Au in Sc and¹⁹³Ir in Be has been determined by Mössbauer measurements. The following values were obtained: (+)4.06(9)10¹⁷ V/cm² for⁵⁷Fe in Sc, ±19.2(4.1)10¹⁷ V/cm² for⁹⁹Ru in Sc, ±11.6(4)10¹⁷ V/cm² for¹⁹⁷Au in Sc, and ±6.4(1.5)10¹⁷ V/cm² for¹⁹³Ir in Be. The results for⁵⁷Fe,⁹⁹Ru and¹⁹⁷Au in Sc are incompatible with the universal correlation between the electronic and the ionic fieldgradient observed in numerous other metals. The data suggest, that a strong contribution to the electric fieldgradient arises from electrons localized at the impurity, if the host is a transition metal and the impurity belongs to the second half of a transition series.     

Mössbauer study of the magnetic and electric hyperfine interaction of dilute57Fe impurities in rare earth metal hosts

The hyperfine interaction of dilute⁵⁷Fe in the rare earth (RE)metals Gd to Lu was investigated by Mössbauer measurements with⁵⁷Co doped RE sources. In all hosts well split, 2-lines spectra were observed at room temperature, with slight asymmetries of the line intensities in some cases. The quadrupole splitting eQV_zz/2 increases from 0.29 mm/sec for Gd to 0.50 mm/sec for Tb, and decreases by less than 10 % between Tb and Lu. Only about 10 % of the corresponding electric fieldgradient (EFG) can be accounted for by the ionic EFG on a substitutional RE site. The temperature dependence of the EFG was measured in the case of Tb. No variation within 3 percent was found between 300 K and 700 K. Measurements of the magnetic hyperfine interaction at low temperatures were carried out in Tb. The saturation field of⁵⁷Fe in this host is H_hf(FeTb;4.2 K)=25(2) KOe. The temperature dependence of the magnetic hyperfine field does not follow the host magnetization (T_c=220K) but vanishes at about 80 K. Similar anomalies of H_hf(T) have previously been observed for other transition element impurities in the RE ferromagnets.     

Beryllium-tetrakis-[trimethylsilyl]-diamid-eine Verbindung mit zweibindigem Beryllium

Monomeres [(CH₃)₃Si]₂NBeN[Si(CH₃)₃]₂ (I) entsteht in 68% Ausb. bei der Reaktion von BeCl₂-Ätherat mit NaN[Si(CH₃)₃]₂. Eigenschaften, IR-, Raman- und¹H-NMR-Spektren sprechen für einen NBeN-Winkel von 180°. Die SiN- und BeN-Valenzkraftkonstanten werden zu 3,40 bzw. 2,96 mdyn/Å errechnet.Monomeric I has been prepared (yield 68%) by the reaction of BeCl₂ with NaN[Si(CH₃)₃]₂ in ether. Properties, infrared, raman and¹H-NMR-spectra support a NBeN angle of 180°. SiN and BeN force constants were calculated to be 3,40 and 2,96 mdyn/Å, respectively.

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9. Mitt. über silylsubstituierte Metallamide; 8. Mitt.:H. Bürger, W. Sawodny undU. Wannagat, J. Organometall. Chem.2, 113, (1965).     

Mössbauer study of magnetic hyperfine interactions in Tb(1−x)Co x intermetallic compounds

Sign and magnitude of the average magnetic hyperfine field H_hf of⁵⁷Fe in Tb_(1?x)Co_x intermetallic compounds have been investigated by Mössbauer spectroscopy. For x>0.5, H_hf decreases linearly with increasing Tb concentration. The sign changes from positive for x<0.8 to negative for x>0.8. These trends are discussed in terms of a simple rigid-band model of the Tb_(1?x)Co_x intermetallics.     

PAC detection of oxide formation in zirconium and hafnium hydrides

The formation of HfO₂ and ZrO₂ oxides in Hf and Zr hydrides has been detected by¹⁸¹Ta PAC spectroscopy. The oxides were identified by their¹⁸¹Ta quadrupole frequency and asymmetry parameter. The growth of the oxide contamination in a H₂ atmosphere has been investigated as a function of temperature and time.     

Magnetic and electric hyperfine interactions of181Ta implanted in thulium

The magnetic and electric hyperfine interaction at the site of dilute¹⁸¹Ta impurities in the rare earth metal Tm has been investigated as a function of temperature by TDPAC measurements. The samples were prepared by ion implantation of radioactive¹⁸¹Hf. In the paramagnetic phase between 100 K and 700 K the electric fieldgradient is a linear function of temperature: V_zz(T)=V_zz(O)·(1-A·T) with A=4.6·10^?4K^?1 and V_zz(293K)=6.4 (4)·10¹⁷v/cm². The TDPAC spectrum observed at 4.2 K reflects the 4 magnetically non-equivalent sites for an impurity in magnetically ordered Tm. The relative values and amplitudes of the corresponding 4 magnetic hyperfine fields are consistent with the predictions of the RKKY theory.     

Rare earth hyperfine interactions studied by perturbed angular correlations

This paper reviews the application of the perturbed angular correlation (PAC/D) technique to studies of rare earth hyperfine interactions. First, PAC/D measurements of the interaction of rare-earth nuclei with the large hyperfine fields of their own partially filled 4f electronic shell are discussed. It is shown that PAC/D spectroscopy is particularly useful for the investigation of 4f spin relaxation in liquid and solid environments, and for the study of the formation and stability of 4f magnetic moments in metallic hosts. The second part of the paper deals with the static hyperfine interaction of non-rare-earth impurity nuclei in the hexagonal, magnetically ordered rare-earth metals. The PAC/D contributions to the systematic investigation of impurity electric field gradients and magnetic hyperfine fields in rare earths are discussed. The importance of PAC/D as the main source of information on the temperature dependence of impurity hyperfine interactions in rare earths is stressed. The trends of the electric field gradients are compared to the behaviour of simpler non-cubic metal systems. The magnetic fields are discussed in the context of current theories.     

Hyperfine spectroscopic study of the metal-insulator transition in V2O3

The metal-insulator (M-I) transition in vanadium sesquioxide V₂O₃ has been investigated by time differential perturbed angular correlation measurements of the electric fieldgradient (EFG) and the magnetic hyperfine field at dilute¹¹¹Cd impurities. The EFG undergoes a first-order change at the M-I transition at T_t=160 K, but does not reflect the high temperature resistivity anomaly. The increase of the EFG with temperature in the metallic phase can be attributed to thermal variations of the oxygen sublattice. The temperature dependence of the magnetic hyperfine field in the insulating phase follows a Brioullin function with a saturation value of H_hf(O)=15 KOe and an extrapolated Neel temperature, which, depending on the impurity concentration, varies between 188 and 230 K.