G.K. Ryasny

Measurements of the hyperfine magnetic fields at Ta and Fe in the Laves compounds (Zrx Hf1−x)Fe2 for 0≤x≤1

The hyperfine magnetic fields at181Ta and57Fe in the ferromagnetic Laves intermetallic compounds (ZrxHf1−x)Fe2 (0≤x≤1) have been measured by the methods of TDPAC and Mössbauer effect, respectively, and shown to be practically independent of x at x≥0.4. An average value Bhf (Ta)=−6.52 T at 300 K was obtained for samples with x≥0.4, and −14.2 T for pure HfFe2 in the hexagonal C14 modification. For 0<x<0.4, a superposition of both field components was observed. A deviation of the temperature dependence of Bhf(Ta) in (Zr0.9 Hf0.1)Fe2 from that for Bhf (Fe) and the bulk magnetization was confirmed, studied in detail, and shown to exist for all x≥0.4. The temperature dependence of Bhf(Ta) in HfFe2 was close to that of Bhf (Fe).

Influence of radiation defects on the hyperfine magnetic field at181Ta in (Zr0.9Hf0.1)Fe2

TDPAC measurements for the 133–482 keV γ-ray cascade in181Ta were performed with181Hf sources in the ferromagnetic Laves intermetallic compound (Zr0.9Hf0.1)Fe2. Two samples, annealed and not annealed after activation of181Hf in a reactor, were investigated. It was shown that in the annealed sample practically all the181Ta daughters occupied regular sites in the cubic Zr(Hf) sublattice and experienced a unique magnetic hyperfine fieldHh.f.(Ta)=−6.38(14) T. In the unannealed source the regular precession was observed only for ≈50% of181Ta nuclei, another half of them were located at some “unobservable” sites due, obviously, to a recoil after the (n, γ) reaction. Possible reasons for discrepancies in the results onHh.f.(Ta) reported in the literature are discussed.

Hyperfine interactions for181Ta nuclei in the laves phases LuFe2 and GdFe2

The hyperfine magnetic fields for181Ta in the cubic (C 15) Laves phases LuFe2 and GdFe2 have been measured by the TDPAC method. At 300 K, Bhf=−20.5(4) T for LuFe2 and +19.0(5) T and +10.2(4) T for the samples of GdFe2, prepared at normal and high (7.7 GPa) pressure, have been obtained. Temperature dependence of these fields in the range 77–900 K has been also measured.

Hyperfine Interactions of 111Cd 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 .

PAC studies of hyperfine interactions of 181Ta in NdFe2

Abstract The cubic Laves phase NdFe 2 was synthesized by melting at the pressure of 8 GPa the constituents with a small admixture of HfFe 2 . The hyperfine magnetic field at Ta at the Nd sites was measured by the PAC method in the temperature range 97–635 K. The value of the hf field extrapolated to T =0 K is -4.7(3) T; it reaches its maximum absolute value 7.2 T at 420 K.

Nuclear 111Cd probes detect a hidden symmetry change at the γ → α transition in cerium considered isostructural for 60 years

We use the time-differential perturbed angular correlation technique to study nuclear electric quadupole hyperfine interactions of probe 111Cd nuclei in cerium lattice sites at room temperature under pressures up to 8 GPa. We have found that the well known γ → α phase transition in cerium is not isostructural. In α-Ce, the probe 111Cd nuclei reveal a quadrupole electron charge density component that is absent in γ-Ce. The hidden spacial structure of electronic quadrupoles in α-Ce is triple-q antiferroquadrupolar, as was suggested in [14]. We relate our findings to the current understanding of the γ → α phase transition and also report on nuclear quadrupole interactions in other high-pressure phases of cerium: α″ (C2/m space symmetry) and α′ (α-U structure).

Magnetic Hyperfine Fields at 181Ta in the samples of GdFe2 Crystallized at High Pressure in the range 3.0 to 6.3 GPa

Abstract The transition from the “normal” electronic state in the cubic Laves intermetallics GdFe 2 into a metastable one, created by melting and crystallization of the samples at high pressure, is studied by TDPAC measurements of the magnetic hyperfine fields at 181 Ta in the samples prepared at 3.0, 5.6 and 6.3 GPa.

PAC studies of hyperfine interactions of181Ta in YBa2Cu3O7-δ and of140Ce in La2CuO4 and La1.85Sr0.15CuO4

Results of TDPAC studies of hyperfine interaction in high temperature superconducting ceramics are reported. The γ-ray cascade of 329–487 keV in140Ce excited in the decay of140La in La2-xSrxCuO4 samples (x=0 and 0.15), and 133–482 keV cascade in181Ta excited in the decay of181Hf in YBa2Cu3O7-δ samples were used. The procedure of introducing radioactive181Hf into the ceramics is described and indirect evidence for the occupation of Cu sites by the181Hf-181Ta probe is presented.

Time-differential perturbed angular correlation studies of in-complexes used in nuclear medicine

For determination of the stability of In3+ complexes with diethylenetriaminepentaacetic acid (DTPA) and newly synthesized chelates-derivatives of 4-amino-2-hydroxybutyric acid in aqueous solutions of pH 1.0–7.5, at room temperature, the time differential perturbed angular γ−γ correlation method was used. Data obtained show that only one of the new ligands forms as strong a complex as DTPA and can be used in water at pH∼7.

Hyperfine interaction of 181Ta in SmFe2

Abstract The magnetic hyperfine field at 181 Ta in SmFe 2 was measured by the TDPAC method in the temperature range from 80 K up to the Curie point. It was shown to rise from 7.1(2) T at 80 K to 8.4(1) T at 300 – 400 K. The results are compared with those for other RFe 2 Laves phases ( R = Y , Nd , Gd , Lu ).