Time Differential Perturbed Angular Distribution Research Articles

Hyperfine fields at Ga66 , Ge67,69 implanted into iron and gadolinium hosts at 6 K, and applications to g -factor measurements

Isomers in $^{66}\mathrm{Ga}$, $^{67}\mathrm{Ge}$, and $^{69}\mathrm{Ge}$ were recoil implanted into ferromagnetic hosts of iron and gadolinium at $\ensuremath{\approx}6$ K, and the hyperfine magnetic fields were determined by time differential perturbed angular distribution (TDPAD) measurements. The hyperfine field strengths at $\ensuremath{\approx}6$ K are compared to the results of previous higher-temperature measurements and the amplitudes of the $R(t)$ functions are compared to empirical expectations. The results show that gadolinium can be a suitable host for high-precision in-beam $g$-factor measurements. The results of new $g$-factor measurements for isomers in $^{66}\mathrm{Ga}$ and $^{67}\mathrm{Ge}$ are $g(^{66}\mathrm{Ga}, {7}^{\ensuremath{-}})=+0.126(4)$, supporting a ${[{\ensuremath{\pi}}_{f5/2}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}]}_{{7}^{\ensuremath{-}}}$ configuration assignment, and $g(^{67}\mathrm{Ge}, 9/{2}^{+})=\ensuremath{-}0.1932(22)$, derived from a new measurement of the ratio $g{(}^{67}\mathrm{Ge})/g{(}^{69}\mathrm{Ge})=0.869(9)$. These values are in agreement with previous results. The $R(t)$ amplitudes indicate that the nuclear alignment produced in the isomeric states was significantly lower than the empirically expected $\ensuremath{\sigma}/I\ensuremath{\approx}0.35$.

Geant4 Simulations of the gSPEC Experimental Apparatus

A new setup (gSPEC) for the measurements of magnetic moments in exotic species is proposed for development at FAIR, the international nuclear facility currently under construction in Darmstadt, Germany. The experimental setup will use a few of the state–of–the–art segmented DEGAS detectors available at GSI, acquire a new large dipole magnet to induce external magnetic fields required for the application of the Time–Differential Perturbed Angular Distribution (TDPAD) technique and integrate ancillary detection systems as part of a research plan to study the properties of exotic species that will made available at FAIR. At the current stage, the envisioned gSPEC setup is still in R&D. Several configurations of the detectors are considered, but optimization relies on detailed simulations of the total efficiency in various geometries. In this work, DEGAS detectors and a split–pole superconducting magnet are studied using the latest GEANT4 simulation package. The simulations aim to offer insight on the detector setup performance before gSPEC is actually constructed.

Hyperfine field of La impurity in Fe host: Experiment and theory

The magnetic hyperfine field of La impurity in ferromagnetic Fe host has been measured by time differential perturbed angular distribution (TDPAD) technique, using the 2738 keV 23/2+, isomeric state in 135La as nuclear probe, populated in the reaction \(^{128}\text {Te}\left ({~}^{11}\mathrm {B}, 4\mathrm {n}\right )^{135}\!\text {La}\) at beam energy of 52 MeV. The spin rotation spectra, R(t) measured in applied field of 2 T showed Larmor precession frequency of ωL = 93.9 ± 4.7 Mrad/sec, which corresponds to a magnetic hyperfine field, Bhf of 42.1 ± 3.3 T. From the sense of rotation observed in the R(t) spectra, the sign of the Bhf has been determined to be negative. Complimenting the experimental studies, we have performed ab-inito calculations of hyperfine field within the frame work of the density functional theory using supercell method. The calculated magnetic hyperfine field shows strong dependence with impurity concentration scaled by the supercell size. For a 2 × 2 × 2 supercell representing La concentration of 6.25 % we obtained Bhf = -21.2 T while, for a 3 × 3 × 3 supercell, corresponding to an impurity concentration of 1.8 % La, the Bhf comes out to be -48.3 T, closely agreeing with our experimental value.

Local magnetism and spin fluctuation behavior of extremely dilute Fe impurity in Pd-U binary alloys: An experimental and theoretical investigation

We report the magnetic behavior of isolated Fe impurity atoms in Pd1−xUx (0 ≤ x ≤ 0.12) alloys studied through measurements of the local susceptibility (χloc) and spin relaxation time for 54Fe nuclear probe using the time differential perturbed angular distribution (TDPAD) technique. With an increase of the U concentration in Pd-U alloys, the magnetic response of Fe, exhibiting Curie-Weiss type χloc(T), reflects a steady decrease of the giant magnetic moment arising from ferromagnetic polarization of host Pd-4d band electrons. Concomitantly, we find an exponential rise in the spin fluctuation temperature TSF. The experimental observation of U induced suppression of giant magnetic moment of Fe in Pd is supported by ab intio electronic structure calculations based on density functional theory. The results presented here support the idea that sign and strength of spin polarization of host conduction band electrons play a crucial role on the spin fluctuation rate and hence moment stability.

Observation of size dependent orbital magnetism of single Fe impurity in nanocrystalline Pb hosts

Employing the time differential perturbed angular distribution (TDPAD) technique we have investigated the local magnetism of single Fe impurity in nanocrystalline Pb matrices, by measuring the local susceptibility and spin relaxation rate of 54Fe nuclei. Compared to the nonmagnetic behavior of Fe in bulk Pb host, characterized by independent local susceptibility χloc(T), the magnetic response of Fe in the nanocrystalline samples with particle size of 10 nm and below exhibit Curie-Weiss like χloc(T) with positive slope, indicating the presence of large orbital magnetic moment on the Fe impurity. The orbital moment of Fe has been estimated to be ∼ 1 µB for 6 nm nano-Pb. Further investigations are being carried out to understand the emergence of orbital magnetism of Fe in nano-Pb.

Spin fluctuation and local magnetism of isolated Fe impurities in Pd1−xVx alloys studied by time differential perturbed angular distribution spectroscopy

The magnetic moment and spin fluctuation temperature of isolated Fe impurity atoms in Pd1−xVx (0 ≤ x ≤ 0.15) alloys have been studied by time differential perturbed angular distribution (TDPAD) technique. With increasing V content in Pd matrix, a large non-linear reduction of the local magnetic moment accompanied with an exponential increase of the spin fluctuation temperature TSF has been observed. At and beyond x = 0.12, the Fe atoms are found to be nonmagnetic. As an important new feature, TSF is observed to vary quadratically with composition dependent changes in host spin polarization.

Anomalous magnetic moment at Ba in Au

The Time differential perturbed angular distribution (TDPAD) technique is employed to measure the local susceptibility at the recoil implanted Ba ions in Au following the nuclear reaction 120Sn(12C, 3nγ)129Ba. We have observed first time the local paramagnetic susceptibility of 5.26(18) at Ba ions comparable to 4f-ions in any non-ferromagnetic metal at room temperature which seems to be related to the electronic s–d and s–f transfer at positive lattice pressure.

Magnetic transition in 122 pnictides XFe2As2 (X=Ca, Sr) probed by hyperfine interaction of 66Ga

Employing the time differential perturbed angular distribution (TDPAD) method we have studied the temperature dependence of the magnetic hyperfine field, Bhf for 66Ga in 122 type pnictides, XFe2As2 (X = Ca and Sr). The saturation hyperfine field, Bhf(0) of Ga in Ca(Sr)Fe2As2 have been observed to be 16.2kG and 22kG respectively. Scaled by the hyperfine field of 66Ga in ferromagnetic elements Fe, Co and Ni, our Bhf(0) data indicate small local moments on Fe, consistent with itinerant type magnetism of these materials. The observed temperature dependence of the hyperfine field data suggests second order type magnetic phase transition with a critical exponent β≈0.22(3) indicating quasi-two dimensional magnetic ordering, possibly due to canting of Fe moments out of the ab plane.

Gfactors of92−and232+isomeric states in129Ba

The time differential perturbed angular distribution (TDPAD) technique has been used to measure the $g$ factor of the 173 keV ${\frac{9}{2}}^{\ensuremath{-}}$ and 2162 keV ${\frac{23}{2}}^{+}$ isomeric states in ${}^{129}$Ba with respect to the known value of the $g$ factor, $\ensuremath{-}0.159(5)$, of the 10${}^{+}$ isomeric state in ${}^{132}$Ba. The measured internal magnetic field at ${}^{132}$Ba in Fe at room temperature is $\ensuremath{-}6.0(2)$ T. The extracted $g$(${\frac{9}{2}}^{\ensuremath{-}}$) value, $\ensuremath{-}0.192(6)$, is consistent with the pure $\ensuremath{\nu}{\frac{9}{2}}^{\ensuremath{-}}$[514] Nilsson configuration while the $g$(${\frac{23}{2}}^{+}$) value, $\ensuremath{-}0.233(7)$, corresponds to the proposed three-quasineutron configuration ${\frac{5}{2}}^{+}$[402]$\ensuremath{\bigotimes}{\frac{7}{2}}^{\ensuremath{-}}$[523]$\ensuremath{\bigotimes}{\frac{11}{2}}^{\ensuremath{-}}$[505] with the admixture of $\ensuremath{\nu}{\frac{7}{2}}^{+}$[404]$\ensuremath{\bigotimes}{\frac{7}{2}}^{\ensuremath{-}}$[523]$\ensuremath{\bigotimes}{\frac{9}{2}}^{\ensuremath{-}}$[514] configuration.

Local probe studies of Fe hyperfine field in CaFe2As2 by time differential perturbed angular distribution (TDPAD) spectroscopy and ab initio methods

Applying the γ-ray perturbed angular distribution technique we have measured the magnetic hyperfine field and spin relaxation time of recoil implanted 54Fe in single and polycrystalline CaFe2As2 over the temperature range 20–360K, encompassing both tetragonal and orthorhombic structural phases of the material. The magnetic response of Fe in the high temperature tetragonal phase (T⩾180K), show Curie–Weiss type local susceptibility and Korringa like spin relaxation, reflecting the presence of localized moment on Fe. In the orthorhombic phase, the spin rotation spectra of 54Fe show two magnetic hyperfine field components, both exhibiting quasi two dimensional magnetic ordering. The experimentally measured hyperfine field and Fe moment show good agreement with results obtained from ab initio calculations performed within the frame work of local spin density approximation (LSDA).

Magnetism of Fe in SrFe2As2: Local investigation by time differential perturbed angular distribution (TDPAD) spectroscopy

Employing the γ-ray perturbed angular distribution technique, we have measured the magnetic hyperfine field of 54Fe in tetragonal and orthorhombic structural phases of SrFe2As2. In the tetragonal phase, the magnetic response of 54Fe shows Curie-Weiss type local susceptibility, indicating the presence of localized moment on Fe. The temperature dependence of the hyperfine field of 54Fe reflects quasi-two dimensional first order magnetic transition at 200 K. Our data indicate that Fe moments in the magnetically ordered phase of SrFe2As2 may be canted out of the ab-plane.

Defect induced magnetism in highly oriented pyrolytic graphite: bulk magnetization and 19F hyperfine interaction studies

We have made bulk and local investigations on defect induced magnetism in highly oriented pyrolytic graphite (HOPG) irradiated with a 40 MeV carbon beam. The local magnetic response of irradiated HOPG was studied by measuring the hyperfine field of recoil implanted 19F using γ-ray time differential perturbed angular distribution (TDPAD) measurements. While the bulk magnetic properties of the irradiated sample show features characteristic of room temperature ferromagnetism, the hyperfine field data reflect enhanced paramagnetism with no indication of long range magnetic ordering. The experimental studies are further supported by ab initio density functional calculations. We believe that the ferromagnetic response in irradiated HOPG arises mostly from defect induced magnetic moments of carbon atoms in the near surface region, while those deep inside the host matrix remain paramagnetic.

Defect induced magnetic interactions in highly oriented pyrolytic graphite (HOPG): a local investigation using TDPAD method

We performed microscopic studies of the magnetic interaction in HOPG by measuring the hyperfine field of 19F using the time differential perturbed angular distribution (TDPAD) technique. The results show two hyperfine fields (Bhf) components: one varying strongly with temperature and saturating around 5 kG, while the other showing a maximum of 0.85 kG. The temperature dependence of Bhf does not show any signature of ferromagnetic ordering, but is reminiscent of enhanced paramagnetism.

Electric quadrupole moments of17/2−and13/2−subsequent isomers inPo209

The electric quadrupole interaction of $^{209}\mathrm{Po}$ high spin isomers in a Bi single crystal has been investigated by the time-differential perturbed angular distribution (TDPAD) technique. A two-level analysis procedure for the $17/{2}^{\ensuremath{-}}$and $13/{2}^{\ensuremath{-}}$ subsequent isomers was employed. The spectroscopic electric quadrupole moments were measured as $|Q(17/{2}^{\ensuremath{-}})|=65.9(7)e {\mathrm{fm}}^{2}$ and $|Q(13/{2}^{\ensuremath{-}})|=12.6(5)e {\mathrm{fm}}^{2}$. The experimental values of equilibrium deformations were extracted.

Magnetic behavior of isolated Mo impurities in antiferromagnetic Cr metal

We report experimental and theoretical studies on the magnetic moment and hyperfine field of isolated Mo impurities in an antiferromagnetic Cr host. The magnetic response of 92,94Mo, measured by means of the time differential perturbed angular distribution (TDPAD) technique, show the saturation hyperfine field B hf ( 0 ) to be − 4.7 T . In addition, we find evidence of short range antiferromagnetic spin correlation above T N , revealed from the observation of large B hf values at temperatures far above T N . Our ab initio calculations, based on the generalized gradient approximation (GGA) of density functional theory (DFT), yield an induced magnetic moment of 0.45 μ B for the Mo impurity in Cr. The magnitude of the calculated hyperfine field B hf cal = − 3.35 T closely agrees with the experimental value. The results presented in this work would be helpful for a common understanding of hyperfine fields of impurity atoms in ferro- and antiferromagnetic materials.

Magnetic hyperfine field of isolated Cu impurities in antiferromagnetic Cr metal:experiment and theory

We report experimental and theoretical studies on the magnetic moment and hyperfinefield of Cu impurity in an antiferromagnetic Cr host. Employing time-differentialperturbed angular distribution (TDPAD) spectroscopy, the saturation hyperfine field,Bhf(0), of62Cu has beenfound to be −4.2 T. From the temperature dependence of the hyperfine field measured in the range 35–350 K we findan indication of paramagnetic short-range spin correlation revealed by the observation of a largeBhf aboveTN. Ourab initio calculations using density functional theory (DFT) show a small induced magnetic moment of≈0.18 μB and a net hyperfinefield of −7.4 T at the Cusite. The theoretical Bhf value agrees with the experimental observation when scaled by the ratioR = μCr(exp)/μCr(calc) between the measured and calculated magnetic moments of Cr.

Spin fluctuations of isolated Fe impurities in Pd-based dilute alloys: effect of ferromagnetichost spin polarization

The magnetic moment and spin fluctuation temperatureTSF of isolated Fe atoms in a number of Pd-based binary alloys, namelyPd0.95M0.05 (M = Ni,Rh, Mo, Ag, Cd, In, Sn, Th and U), have been determined from the local susceptibilityχloc(T) of54Fe probe nuclei measured by means of the time differential perturbedangular distribution (TDPAD) technique. Depending on the element Madded to the Pd matrix, the results derived from Curie–Weiss analysis,χloc(T) = C/(T+TSF), reveal strong enhancement or suppression of the ferromagnetic host spin polarizationSh associated with the giant moment of Fe. Concurrent with the variation in host spinpolarization, we have observed a large change in the spin fluctuation temperatureTSF, showing an exponential rise with diminishing value ofSh. The results, analysed on the basis of the Kondo model, indicate that spin fluctuationscaused by the antiferromagnetic interaction associated with the negative conductionelectron spin polarization are suppressed progressively by an incremental addition of apositive contribution to the effective exchange interaction.

Measurement of the g-Factor of the 27− High-Spin Isomer State of 152Dy

The g-factor of the 27− isomer state of 152Dy has been measured using the Time- Integral Perturbed Angular Distribution (TIPAD) method. The high-spin states of 152Dy have been populated by 141Pr(16O,p4n)152Dy reaction at E = 115 MeV from the AVF cyclotron at CYRIC. The paramagnetic correction factor of Dy ions in Pr has been determined to be 4.2(5) by the Time- Differential Perturbed Angular Distribution (TDPAD) measurement of the 21− state of 152Dy. As a result, the g-factor of the 27− isomer state of 152Dy has been obtained to be +0.09(5). This shows the smaller value than the expected one of +0.39 deduced from a fully aligned configuration of π(h 11 2/2 ) ⊗ v(f 7 2/2 h 9/2 i 13/2).

G-Factor of the high-spin isomer in 149Dy and a multi-quasiparticle configuration caused by the N=82 core excitations

The nuclear g-factor of the T 1/2 = 28 ns high-spin isomer in 149Dy has been measured using the γ-ray time-differential perturbed angular distribution (TDPAD) technique with a pulsed beam of 132Xe. The experimental value g=+0.41(6) is in good agreement with a fully aligned multi-quasiparticle configuration π( h 2 11/2)⊗ ν( f 7/2 h 9/2 i 13/2( d −2 3/2) 0). This result indicates that only neutron particle–hole excitations across the N=82 shell-closure occur at this isomeric state.

Locations of implanted 19F* atoms in Si, Ge and diamond studied through their nuclear quadrupole interactions

The Hartree-Fock cluster procedure was used to obtain the associated electronic distributions for 19F* (I = 5/2, Ex = 197 KeV excited nuclear state of the 19F atom) at possible sites in crystalline Si, Ge and diamond and to calculate nuclear quadrupole coupling constants vQ and the asymmetry parameter η of the electric field gradient at the modelled sites. Lattice relaxation effects have been incorporated by employing a geometry optimization method to obtain minimum energy configurations for the clusters modelling each site. The intrabond (IB), antibonding (AB) and substitutional (S) sites in the bulk and the atop site on the surface were studied. From a comparison with vQ and η values observed in time differential perturbed angular distribution (TDPAD) measurements we were able to identify the high frequency component in Si and Ge with 19F* at the intrabond site. In diamond two high frequency components are observed. These are identified with 19F* at intrabond and substitutional sites. For the low frequency site in Si and Ge the assignment is made to 19F* implants at dangling bonds in the bulk resulting from implantation damage. In diamond none of the sites studied could provide lower frequency nuclear quadrupole parameters close to the observed ones.