Hyperfine field at 181Ta nuclei in ferromagnetic ZrZn2

A sample of ZrZn₂ containing 2% Hf has been studied by differential perturbed angular correlations of the gamma rays of ¹⁸¹Hf. A value of -15.1 ± 0.6 kOe was found for the hyperfine field at the ¹⁸¹Ta nuclei.     

Perturbed angular correlation measurement of theg-factor of the 668keV state in132Xe

A valueg=0.38±0.06 was obtained for theg-factor of the 668 keV state of¹³²Xe (τ=7.3±0.6 psec) from time-integral perturbed angular correlation measurements on gamma cascades in¹³²Xe. Sources of¹³²Te implanted in iron were used to obtain a magnetic hyperfine field of 1510±100 kG at the¹³²Xe nuclei.     

Investigation of the impurity hyperfine field polarization in polycrystalline Rare Earth ferromagnets

Time differential perturbed angular correlation spectra of¹¹¹Cd in ferromagnetic polycrystalline Dy have been measured at 4.2 K in external magnetic fields up to 60 kG. The experimental data were well reproduced by a calculation which assumed that the angular distribution of the magnetic hyperfine fields is identical to that of the magnetic moments of the 4f-shells. The distribution of the 4f-moments was derived from magnetic anisotropy data. The results of this work seem to justify the application of the integral perturbed angular correlation technique for the determination of magnetic hyperfine fields in incompletely polarized ferromagnetic samples. The magnetic hyperfine fields of¹⁷⁷Hf:Gd and¹⁷⁷Hf:Dy have been measured by this method as:H _hf(Hf:Gd)=–375(60)kG andH _hf(Hf:Dy)=–225(45)kG.     

Magnetic hyperfine fields at Fe,Cd and Sn sites in an FeCo alloy

The magnetic hyperfine field at an Fe site in the ferromagnetic alloy Fe_0.475Co_0.525 was measured using the Mössbauer effect. The value obtained at room temperature was 343 kOe. The hyperfine field at a substituted Cd impurity was measured by the method of time differential perturbed angular correlations. A single frequency was observed at room temperature, corresponding to a field of -177 kOe. Using the Mössbauer effect, the Sn site hyperfine field was measured in a sample in which 0.3 atomic percent of ¹¹⁹Sn had been substituted. The room temperature spectrum consisted of the superposition of a single line, together with a six-line hyperfine spectrum, corresponding to a field of 231 kOe. A phenomenological interpretation is proposed for Fe, Cd and Sn fields in the binary alloys of iron.     

Magnetic hyperfine fields at Ta in Co and Fe hosts measured by the e−-γ time-differential perturbedangular-correlation method

The radioactivity¹⁸¹Hf was implanted into pure Co and Fe hosts with the help of an isotope separator. The ferromagnetic hosts produce very strong magnetic hyperfine interactions at the nuclear site of Ta atoms. These hyperfine interactions were studied by time-differential measurements of the 133 keV conversion electron — 482 keV γ angular correlation. It is found that in both hosts an appreciable fraction of Hf atoms occupies regular lattice sites after the implantation. Using the knowng-factor of the 482 keV state of¹⁸¹Ta the magnetic hyperfine fieldsH _hf=±362.4(5.0) and ±596(18) kG for the Co and Fe hosts, respectively, were deduced These fields fit nicely into the systematics of the hyperfine fields for the 5d transition elements but are not well accounted by the existing theoretical models.     

Magnetic hyperfine fields on 111Cd in the Pd1+xMnSb heusler alloys

The time-differential perturbed angular correlation technique has been used to measure the magnetic hyperfine fields (mhf) acting on ¹¹¹Cd impurity on the series of alloys Pd_1+xMnSb with 0 ? x ? 1. We observe three diffrent mhf's which for small values of x are of the order of +250, ?250 and ?150 kOe, decreasing slowly for larger values of x. These three fields are associated with ¹¹¹Cd occupying the sites of Mn, Sb and Pd, respectively. In addition, magnetization measurements on three of the allows (x = 0, 0.4 and 0.8) gave magnetic moments on the Mn atoms of 3.88 ± 0.08, 4.18 ± 0.08, (4.14 ± 0.08)_μB and Curie temperatures of 470 ± 2,422 ± 5 and (288 ± 2) K, respectively. Our results together with the existing data for mhf's on various 5sp elements in the Pd₂MnSb Heusler alloy are compared with the Blandin-Campbell model and show an agreement which is only qualitative.     

Hyperfine interaction experienced by181Ta nuclei at the Hf site in HfFe2−xSix compounds through a decoupling experiment

The time-differential perturbed angular correlation (TDPAC) experiments involving the 133–482 keV γ-γ cascade in¹⁸¹Ta have been performed in the presence of an external magnetic field along the quantization axis to measure the hyperfine magnetic field experienced by¹⁸¹Ta nuclei at the Hf site in the pseudobinary compounds HfFe_2?xSi_x with x=0.1 and x=0.3. The hyperfine magnetic fields measured at 298 K are H_hf=133.1±12.0 kG in the cubic (C15) Laves phase compound HfFe_1.9Si_0.1 and H_hf=76.8±7.0 kG in the hexagonal (C14) Laves phase compound HfFe_1.7Si_0.3. The measured hyperfine fields are discussed within the framework of the Campbell-Blandin model.     

Internal magnetic hyperfine fields at Hf nuclei in iron,cobalt and nickel hosts

Integral perturbed angular correlation technique has been used to measure the internal hyperfine magnetic fields at Hf nuclei in Fe, Co and Ni matrices. These represent a consistent set of measurements with diffused sources. The 9+/2 (208 keV) 9?/2 (113 keV) 7?/2 cascade in the decay of¹⁷⁷Lu→¹⁷⁷Hf was used for measurements. The results obtained are: $$\begin{gathered} H_{Fe}^{Hf} = - 266 \pm 47 kG, \hfill \\ H_{Co}^{Hf} = - 116 \pm 18 kG, \hfill \\ H_{Ni}^{Hf} = - 118 \pm 26 kG. \hfill \\ \end{gathered} $$ These measurements are compared with previous results and discussed in terms of methods of source preparation.     

Hyperfine field of Lu in Fe and Ni and annealing properties of the FeYb implanted alloy

Integral perturbed angular correlation measurements of the hyperfine field at ¹⁷⁵Lu isotope-separator implanted in Fe and Ni yield fields of −(575 ± 41) kOe and −(130 ± 27) kOe, respectively. A clear annealing stage is found around 450°C.     

Magnetic HFI of cerium in an iron garnet investigated by angular correlations

The magnetic HFI of cerium ion in a lanthanum-doped yttrium iron garnet is investigated by the gamma-gamma angular correlation technique. It is found that cerium, formed after radioactive decay of La¹⁴⁰, reaches the ground state of Ce³⁺ in a time short compared with the nuclear state life-time of 4.9 nsec. Quasi-static as well as time-dependent interactions are detected, yielding an internal field ofH _eff=(21.5± 3) kOe at the nuclei of cerium. The molecular field theory is applied in the analysis of data, and values for the exchange field, the spinlattice relaxation time and the magnectic moment of cerium ion in an iron garnet at room temperature are deduced. These values are:H _exch=(147±20)kOe, τ _c =(4.5±0.6)×10^?13 sec and 〈μ_z〉=(0.017±0.002) Bohr magnetons.     

Hyperfine critical exponents β and δ of tantalum in nickel

The hyperfine critical coefficients β and δ on dilute ¹⁸¹Ta nuclei in a nickel matrix have been measured using the time differential perturbed angular correlation technique. We find: β = 0.041₇ ± 0.01₀, δ = 4.1 ± 0.3. They are somewhat different from the values deduced from the bulk magnetization measurements on pure nickel.     

Nuclearg factors of the first and second 2+ states in192,194Pt

Theg factors of the first and second excited 2⁺ states in¹⁹²Pt and¹⁹⁴Pt have been measured using γ-γ angular correlations perturbed by the hyperfine field in an iron lattice. Bulk magnetizations of sources were examined with special care for different shapes of alloys and different magnetizing conditions. The following results have been obtained:¹⁹²Pt: 316 keV stateg=0.346±0.024, 612 keV stateg=0.455±0.089.¹⁹⁴Pt: 328 keV stateg=0.354±0.031, 622 keV stateg=0.316±0.029. These values are the largest ones which have been reported so far. The discrepancies between the present and previous data are discussed especially in terms of magnetizing conditions for the sources used. It is suggested that the difference ing factor between the first and second 2⁺ states may be in a certain correlation with M1 matrix element connecting these two states.     

Quadrupole interaction at Ta and lattice location of Hf in Be

The time-differential perturbed angular correlation technique (TDPAC) has been applied to the 482 keV excited state of¹⁸¹Ta, to determine the nuclear electric quadrupole interaction (QI) at Ta in Be. Sources were prepared by ion-implantation of¹⁸¹Hf in Be. Particle channeling measurements have revealed that. Hf impurities implanted in Be reside primarily at the tetrahedral interstitial site. The fundamental QI frequency obtained for Ta at this interstitial site in Be is |v _Q| =e ² qQ/h = 227.0 ± 2.2 MHz which corresponds to an electric field gradient |eq|=(3.71±0.15)×10¹⁷ V/cm². This result is discussed in terms of results for Cd impurities in the same system and the systematics of the impurity QI in metals.     

Perturbed angular correlation study of a nanostructured HfO2 film

The hyperfine field at ¹⁸¹Ta lattice sites in a nanostructured HfO₂ thin film was studied by the perturbed angular correlation (PAC) technique. The thin oxide film was deposited by pulsed laser ablation on a silicon substrate kept at 673 K. The thickness was about 25 nm. The radioactive ¹⁸¹Hf ions were produced by neutron activation of the very thin film in the Portuguese research reactor by the reaction ¹⁸⁰Hf(n,γ)¹⁸¹Hf. PAC measurements were carried out at room temperature after annealing at different temperatures up to 1,473 K in air. The PAC technique allows determining the electric field gradient at the ¹⁸¹Ta probe sites. The ¹⁸¹Ta isotopes appear in the sample as disintegration product of ¹⁸¹Hf.     

Decoupling experiments for the study of electric and magnetic hyperfine interactions in ferromagnetic compounds

The decoupling experiments involving the time-differential perturbed angular correlation (TDPAC) of the 133–482 keV γ-γ cascade in the presence of an external magnetic field applied along the quantization axis have been performed to measure the electric quadrupole and the magnetic hyperfine interactions experienced by the¹⁸¹Ta nuclei at Hf sites in the pseudobinary compounds HfFe_2-xSi_x, withx=0.1 andx=0.3. The hyperfine magnetic fields measured at 298 K areH _hf=133.1±12.0 kG in the cubic (C15) Laves phase compound HfFe_1.9Si_0.1 andH _hf=76.8±7.0 kG in the hexagonal (C14) Laves phase compound HfFe_1.7Si_0.3. The decoupling technique has also been used to obtain a —ve sign for the hyperfine field experienced by¹⁸¹Ta nuclei at the Ti or Hf sites in the Heusler compound Co₂Ti_0.8Hf_0.2Sn and a+ve sign for the hyperfine field at Zr sites in the cubic (C15) Laves phase compound ZrFe₂.     

The g-factors of the first 2+ states in 50, 54Cr, 54Fe and 70Ge

The gyromagnetic ratios of the first excited J^π = 2⁺ states of ^50,54Cr, ⁵⁴Fe and ⁷⁰Ge have been determined by the ion-implantation perturbed angular correlation technique (IMPAC) with ferromagnetic Gd as stopping material. The g-factors were extracted from the measured precession angles with use of known lifetimes, static hyperfine magnetic fields and transient hyperfine magnetic field data for fast ions traversing ferromagnetic lattices. The deduced values are 0.59 ± 0.10, 0.56 ± 0.10, 1.08±0.19 and 0.38±0.08, respectively. With the exception of ⁵⁴Fe all g-factors are close to the collective value. A re-evaluation of earlier IMPAC data on ^{70, 72, 74, 76}Ge with Fe as stopping material has been performed. The value obtained for ⁷⁰Ge is in good agreement with the one measured in this work.     

Hyperfine field measurements on dilute scandium in cobalt matrix

Using the time differential perturbed (γ-γ) angular correlations technique (TDPAC), the hyperfine field (H_hf) at ⁴⁴Sc nuclei in cobalt matrix is measured for the first time and the value obtained is H_hfSc$\text{Co}$(RT) = -58±4 KOe. The measured hyperfine field value is compared with the predictions of the existing hyperfine field models.     

The magnetic hyperfine field of 111Cd in the light rare earth metal neodymium

The magnetic hyperfine field of the non-magnetic impurity ¹¹¹Cd in the light rare earth metal Nd has been determined by a perturbed angular correlation (TDPAC) measurement to be |H_hf| = 76.5 (1.5) kOe at 4.2 K. This value fits excellently into the linear relation between H_hf and the rare earth spin projection (g − 1)J observed for ¹¹¹Cd in the heavy rare earth series Gd to Tm. The data suggest a maximum of the s-f coupling constant J(0) for Sm.     

Temperature-dependent hyperfine interactions at 111Cd-C complex in germanium

The temperature dependent nuclear hyperfine interaction of ¹¹¹Cd-carbon complex in germanium has been studied using the perturbed γ–γ angular correlation (PAC) method. The parameters of the hyperfine interaction representing substitutional carbon–cadmium complex in germanium (ν _Q1=207(1) MHz (η=0.16)) shows dependence on temperature. The formation and thermal stability of the complex has been reported by the same author earlier. It was found in this study that the quadrupole coupling constant of the interaction increases at sample temperature below 293 K. The results are encouraging toward better understanding of the complex in the host matrix.     

A simple digital TDPAC spectrometer

We present a simplified digital time differential perturbed γ???γ angular correlation (TDPAC) spectrometer that demonstrates that such instruments can be built using primarily commercial components and with relatively modest coding effort. The system handles data rates of 70 kcps/detector with a timing resolution of better than 500 ps, and has been used with both ¹¹¹In and ¹⁸¹Hf.