Fe Host Research Articles

G-Factors of the ground states of 95Nb and 96Nb

Nuclear magnetic resonance measurements have been performed for 95 Nb and 96 Nb oriented at 7 mK in an Fe host. The magnetic hyperfine splitting frequencies, v = ∥ gμ N B h.f/ h∥, of the 95Nb and 96Nb ground states were determined to be 275.16(8) and 167.20(1) MHz. With a hyperfine field of B h.f. = — 264.54(19) kG the nuclear g-factors were deduced to be ∥g( 95 Nb, 9 2 +)∥= 1.3645(13) and ∥g( 95 Nb, 6 +)∥ = 0.8292(7) .

Nuclear spin-lattice relaxation of dilute V, Cr and Mn in iron at very low temperatures

We report determinations of the spin-lattice relaxation rates of dilute 48V, 51Cr and 54Mn nuclei in polycrystalline Fe host at very low temperatures. The high-field limiting rates for FeV and FeMn agree well with earlier spin-echo results. The rate for Fe Cr fits the systematics and is in agreement with a recent ab initio calculation. A dependence of the relaxation rates on applied magnetic field was observed, similar to that seen for other impurity nuclei in Fe.

Magnetic moments at backbending and spectroscopy of 134Ce

Employing the static hyperfine fields at cerium nuclei in magnetized Fe and Gd hosts, the g-factor of the 134Ce(10 +) state at backbending ( E x = 3719.3 keV) has been determined as g = − 0.30 (25). The coexistence of this neutron-dominated state with the ( v h 11 2 ) n 10 + isomer ( E x = 3208.5 keV, g = −0.19(1)) is unexpected. A comprehensive spectroscopic study following the 122Sn( 16O, 4n) reaction, including γ-angular distributions, prompt and delayed γ coincidence and recoil-distance measurements has yielded new information on quasi-collective bands of both parities. The properties of the low-lying positive-parity states are well described by the interacting boson model.

Transition-metal impurities in diluteFe3−xTxSialloys: A spin-echo NMR investigation

A comprehensive collection of spin-echo NMR spectra from nuclei of both host and transition-metal impurities ($T$) in pseudobinary ${\mathrm{Fe}}_{3\ensuremath{-}x}{T}_{x}\mathrm{Si}$ alloys taken at about 1.3 K are presented and analyzed. We summarize some new data on $3d$ elements and also review briefly some results already reported. Previously unpublished results for $4d$ and $5d$ elements are reported. ${\mathrm{Fe}}_{3}$Si has two inequivalent Fe sites and one Si site. From the analysis of the solute spectra we show that the $3d$, $4d$, and $5d$ elements under Fe or to the right of Fe in the periodic table (Ni, Co, Ru, Pd, Os, and Ir) enter the Fe site with four Fe and four Si first neighbors. The $3d$ elements to the left of Fe (Mn, V, Cr, and Ti) enter the Fe site which has eight Fe first neighbors. In addition, we report that in Fe-rich nonstoichiometric alloys Ni, Ru, Rh, and Pd prefer $A$, $C$ sites with the smallest number of Fe first neighbors. The roles of electronic structure, electronegativity, and atomic size in producing the observed selectivity are analyzed. Finally a comparison between impurity hyperfine fields in ${\mathrm{Fe}}_{3}$Si and Fe, Ni, and Co hosts is made. The dependence of impurity hyperfine fields on both the moment of the host and the position of the impurity in the periodic table, found for Fe, Ni, and Co hosts, are also shown to exist in the case of ${\mathrm{Fe}}_{3}$Si alloys. Using these dependences, we make tentative predictions of the fields at some nuclei for which spectra were not observed.

NMR-ON of182Ta and183Ta in Fe

Nuclear magnetic resonance has been observed on radioactive182Ta and183Ta oriented at low temperature in an Fe host, by detection of the change in spatial anisotropy of γ-rays emitted during nuclear decay. By measuring the resonant frequencies of183Ta in four different applied magnetic fields the nuclear magnetic moment and hyperfine field have been deduced. These are: $$|\mu \left( {{}^{183}Ta; I = \tfrac{\user2{7}}{\user2{2}}} \right)| = 2.28(3)\mu _{\rm N} and B_{hf} \left( {Ta\underline {Fe} at 0 K} \right) = - 67.2(1.3)T$$ . The spin of the ground state of182Ta has been determined asI=3 by comparing resonance results with those obtained in a thermal equilibrium nuclear orientation study. The ratio of the resonant frequencies observed for182Ta and183Ta at one applied field value yields a magnetic moment for the former of $$|\mu \left( {{}^{182}Ta; I = \user2{3}} \right)| = 2.91(3)\mu _{\rm N} $$ . The spin lattice relaxation time for183TaFe (0.12 at% Ta) at 18 mK in an applied field of 0.5 T has been found to be 40(10) s.

A channeling study of Sb trapping in Fe-Ti-C-Sb alloys

The trapping site for Sb in an Fe crystal containing TiC precipitates has been determined using channeling techniques in ion backscattering and ion-induced characteristic x-ray analyses of ion-implanted alloys. From the orientation of the TiC particles relative to the Fe host lattice, we show that ≳60% of the trapped Sb atoms occupy Fe sites at the Fe-TiC interface, rather than Ti sites within the TiC particles.

NMR-on of182Ta and183Ta in Fe

Nuclear magnetic resonance has been observed on radioactive182Ta and183Ta oriented at low temperature in an Fe host, by detection of the change in spatial anisotropy of γ-rays emitted during nuclear decay. By measuring the resonant frequencies of183Ta in four different applied magnetic fields the nuclear magnetic moment and hyperfine field have been deduced. These are: $$|\mu \left( {{}^{183}Ta; I = \tfrac{\user2{7}}{\user2{2}}} \right)| = 2.28(3)\mu _{\rm N} and B_{hf} \left( {Ta\underline {Fe} at 0 K} \right) = - 67.2(1.3)T$$ . The spin of the ground state of182Ta has been determined asI=3 by comparing resonance results with those obtained in a thermal equilibrium nuclear orientation study. The ratio of the resonant frequencies observed for182Ta and183Ta at one applied field value yields a magnetic moment for the former of $$|\mu \left( {{}^{182}Ta; I = \user2{3}} \right)| = 2.91(3)\mu _{\rm N} $$ . The spin lattice relaxation time for183TaFe (0.12 at% Ta) at 18 mK in an applied field of 0.5 T has been found to be 40(10) s.

Calculation of the transferred hyperfine field (volume overlap) contribution on nonmagnetic impurities in Fe and the Heusler alloys

The transferred hyperfine fields (hff) at 4sp and 5sp solute atoms in Fe and the sp sites of the Heusler alloys have been calculated using a volume overlap model. The main difference between this and previous calculations is that the host wavefunction in the solid is represented by an orbital that is simulated from band calculations. The contributions from 2nn and 3nn atoms are also included. The calculated transferred hff values are compared to the hff contributions obtained by substracting the hff due to the host s conduction electron polarization from measured hff values. For the 4sp and 5sp impurities in Fe the calculated transferred hff contributions agree excellently with those obtained from the measured hff. The experimental data for sp impurities at the Z site of Heusler alloys is less complete than that for an Fe host, but again the calculated transferred hyperfine fields agree satisfactorily with those deduced from the measured values. Since for the Heusler alloys there are no arbitrary procedures or parameters relative to the Fe data, the agreement between the calculated and experimental values gives strong evidence in support of the volume overlap model.

Magnetic ordering in exchange-enhanced(Pd1−yAgy)100−xFexand(Pd1−yRhy)100−xFexalloys

Magnetization measurements are reported for several ${\mathrm{Pd}}_{1\ensuremath{-}y}{\mathrm{Ag}}_{y}$ and ${\mathrm{Pd}}_{1\ensuremath{-}y}{\mathrm{Rh}}_{y}$ host alloys doped with $x=0.5\ensuremath{-}, 1.0\ensuremath{-}, \mathrm{and} 2.0\ensuremath{-}\mathrm{at}.%$ Fe to form ${({\mathrm{Pd}}_{1\ensuremath{-}y}{\mathrm{Ag}}_{y})}_{100\ensuremath{-}x}{\mathrm{Fe}}_{x}$ (where $0\ensuremath{\le}y\ensuremath{\le}0.50$) and ${({\mathrm{Pd}}_{1\ensuremath{-}y}{\mathrm{Rh}}_{y})}_{100\ensuremath{-}x}{\mathrm{Fe}}_{x}$ (where $0\ensuremath{\le}y\ensuremath{\le}0.75$). The experiments were carried out with a vibrating-sample magnetometer at temperatures ranging from 3\ifmmode^\circ\else\textdegree\fi{}K to room temperature and for fields up to 20 kOe. The dependences of the paramagnetic susceptibility, effective magnetic moment, and magnetic-ordering temperature on the Fe concentration and host matrix susceptibility (and, consequently, the electronic structure) were explored and the results provide some support for the existing molecular-field theories that describe the region of ferromagnetic ordering in exchange enhanced alloys. From the observed linear dependence of the ordering temperature on the host-matrix susceptibility and the saturation moment per Fe atom, values were obtained for the molecular-field coefficient (describing the localized moment to Pd $4d$-electron interaction), $\ensuremath{\alpha}$, and the exchange-interaction constant, $J$. For the ${({\mathrm{Pd}}_{1\ensuremath{-}y}{\mathrm{Ag}}_{y})}_{100\ensuremath{-}x}{\mathrm{Fe}}_{x}$ system, we find $\ensuremath{\alpha}=1.1\ifmmode\times\else\texttimes\fi{}{10}^{3}$ mole/emu and $J=0.071$ eV, while for ${({\mathrm{Pd}}_{1\ensuremath{-}y}{\mathrm{Rh}}_{y})}_{100\ensuremath{-}x}{\mathrm{Fe}}_{x}$, $\ensuremath{\alpha}=1.3\ifmmode\times\else\texttimes\fi{}{10}^{3}$ mole/emu and $J=0.084$ eV.

Coulomb and exchange scattering amplitudes from spin dependent residual resistivities in Fe and Ni hosts

The spin dependent residual resistivities for a large number of solute atoms in Fe and Ni based ternary alloys are analyzed as arising from three main sources. 1. Coulomb scattering from the impurity charge (or volume) perturbation. This amplitude is found to be similar to that for Cu based alloys. 2. Scattering from a localized moment perturbation at the solute atom. Both a potential and exchange amplitude are found to be spin-dependent and about the same per μB for Fe and Ni hosts. 3. A more widespread moment perturbation in the host surrounding the solute atom. The shape of this perturbation depends upon whether direct Coulomb exchange or hybridization effects dominate. In Ni, usually hybridization effects dominate and give predominately negative host perturbations. In Fe, Coulomb exchange dominates and the shape of the host perturbation depends upon the number of itinerant d-like electrons connected with the solute atom.

Review paper: ?Brute-force? nuclear orientation: A survey of accomplishments and problems to date

The technique of “brute-force” or direct low-temperature nuclear orientation has become practicable since about 1970 with the development of cryostats capable of producing the required combination of fields and temperatures. This is reflected in the increasing number of experiments reported in recent years. We summarize here the potential applications and some of the initial difficulties of the technique. New data for the systems95TaTa,110Agm Ag and CoMo are presented, and the results of a magnetic resonance experiment on95Nb nuclei oriented by the direct method are compared with data from a conventional resonance experiment in Fe host.

The lattice location and hyperfine field of implanted Yb in Fe as a function of annealing temperature

A combined study has been made of the lattice location and hyperfine field of Yb implanted into Fe single crystals. The location has been determined by ion channeling and back-scattering, the hyperfine field by perturbed angular correlation (PAC) measurements on169Yb (decaying to excited states in169Tm). The channeling experiments indicate that initially about 60% of the Yb atoms occupy substitutional sites in the Fe lattice, while the remaining atoms are not in any specific crystallographic site. On annealing, Yb migrates from substitutional to non-substitutional sites. No Yb atoms remain substitutional after a 600°C anneal. By making PAC measurements at two temperatures for two γ-γ cascades in169Tm, it is found that the PAC pattern can be described using a combined static and time-dependent magnetic interaction. The PAC results show that the average hyperfine field and relaxation parameter decrease on annealing, and that the field disappears after a 600°C anneal. The correlation between the location and the hyperfine field is discussed. A comparison of the results with previous Mossbauer results for151Gd implanted in Fe, together with relaxation parameter measurements on a169Yb2O3 source, suggests that the non-substitutional Yb is internally oxidized in the Fe host.

Nuclear orientation of105Rh and95Tc in iron

The temperature-dependent anisotropy of γ-rays following the decay of oriented95Tc and105Rh nuclei was studied with a Ge(Li) detector. Mixing coefficients of some γ-and preceding β-transitions, the spins of two intermediate levels, and the magnetic hyperfine splitting of the95Tc and105Rh ground states in an Fe host were measured. From the known hyperfine fields the following magnetic moments were deduced:

Hyperfine fields at non-magnetic sites in metals

The conduction electron polarization contribution to the hyperfine fields at s-p sites in magnetic metals is discussed using an RKKY-like model in which the effect of the charge at the s-p site is included explicitly. It is shown that this mechanism alone can provide a simple explanation for observed hyperfine systematics in a variety of systems, in particular for s-p elements in Heusler alloys and for s-p impurities in Fe, Ni or Pd hosts.

Magnetic hyperfine fields at Ta in Co and Fe hosts measured by the e?-? 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 fieldsHhf=±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.

Electric quadrupole intermediate state perturbations in nuclear orientation with particular reference to Bi isotopes in Fe and Ni

The effect on the radiation angular distribution from oriented nuclei of combined magnetic dipole and electric quadrupole interactions of comparable strengths in long lived intermediate states is studied. The particular relevance of such studies to the nuclear orientation of dilute bismuth impurities in the ferromagnetic metals is demonstrated and evidence for similarity of the nonsubstitutional sites occupied by the bismuth atoms in Fe and Ni hosts is briefly discussed.

Combined lattice-location-hyperfine-interaction experiment on Se implanted in Fe and Co

The channeling technique has been used to study the lattice location of Se implanted into Fe and Co (hcp) single crystals. For both systems the impurity is found to be fully substitutional at doses of 5 \ifmmode\times\else\texttimes\fi{} ${10}^{14}$ ${\mathrm{cm}}^{\ensuremath{-}2}$. Nuclear-orientation measurements at mK temperatures have been made on implanted $^{75}\mathrm{Se}$ in Fe and Co polycrystalline hosts. Nuclear magnetic resonance of oriented nuclei (NMR/ON) was observed for Fe $^{75}\mathrm{Se}$ at 141.6 MHz (${H}_{\mathrm{ext}}=0$) and a resonance-shift experiment yields $|\ensuremath{\mu}(^{75}\mathrm{Se})|=(0.67\ifmmode\pm\else\textpm\fi{}0.04){\ensuremath{\mu}}_{N}$ and ${H}_{\mathrm{hf}}(Fe\mathrm{Se})=690\ifmmode\pm\else\textpm\fi{}50$ kG. For CoSe no NMR/ON signal was observed, but the temperature-dependent $\ensuremath{\gamma}$ anisotropy is fitted to yield ${H}_{\mathrm{hf}}(Co\mathrm{Se})=+420\ifmmode\pm\else\textpm\fi{}40 \mathrm{kG} or\ensuremath{-}440\ifmmode\pm\else\textpm\fi{}40 \mathrm{kG}$ although these values make no allowance for possible quadrupole interactions at the hcp lattice site. In the analysis of the Fe $^{75}\mathrm{Se}$ nuclear-orientation experiment, the $\ensuremath{\delta}(\frac{E2}{M1})$ mixing ratios of the 280- and 265-keV transitions determined. These results are compared with recent intermediate-coupling collective-model calculations.

The Ratio of the Nuclear Moments of 99Ru and 101Ru from NMR Studies of Ferromagnetic Alloys

NMR investigations of Ru as an impurity in Fe, Co, and Ni hosts yield a resonance frequency ratio for the isotopes 99 Ru and 101 Ru, ν 101 /ν 99 =1.121±0.002 Interpreting this as the ratio of nuclear moments and using the best available date for µ 99 gives µ 101 =0.698±0.024 µ N .

Measurements of the Magnetic Hyperfine Fields at Hg in Fe, Co, and Ni Hosts by thee−−γTime-Differential Perturbed-Angular-Correlation Method

The $^{197m}\mathrm{Hg}$ radioactivity was implanted into pure-Fe, -Co, and -Ni hosts with the help of an isotope separator. These ferromagnetic hosts produce strong magnetic hyperfine interactions at the nuclear site of the Hg atoms. These hyperfine interactions were studied by time-differential measurements of the 165-keV $L$-conversion ${e}^{\ensuremath{-}}$-134-keV $\ensuremath{\gamma}$ angular correlation. Measurements with both nonmagnetized and magnetized foils were performed. By use of the quite accurately known g factor of the 134-keV state of $^{197}\mathrm{Hg}$, the magnetic hyperfine fields $|{H}_{\mathrm{int}}|=692\ifmmode\pm\else\textpm\fi{}55,483\ifmmode\pm\else\textpm\fi{}40, \mathrm{and} 103\ifmmode\pm\else\textpm\fi{}8$ kG for the Fe, Co, and Ni lattices, respectively, were deduced.

Magnetic hyperfine field at 206Bi in Ni

Radioactive 206Bi has been dissolved in Ni and polarized at very low temperatures via magnetic hyperfine interaction. The derived magnetic hyperfine field at Bi in Ni is 390 ± 15 kG. Similar experiments in an Fe host confirm the intractability of the system Bi/Fe.