Nuclear magnetic resonance of brute force oriented110mAgAg

NMR on brute force oriented nuclei (NMRON/BF) has been observed for^110mAg in elemental silver. Resonances have been measured at approximately 7 T and 8 T with the resulting gradient of 4.583(5) MHzT⁻¹ which produces a value for the^110mAg moment of μ=3.589(4) nm (uncorrected). Factors pertinent to successful NMRON/BF in systems such as^110mAgAg, with a complex decay scheme and modestg-factor, are also discussed.     

MAPON EFG Result for 54Mn in Cubic Cobalt

Modulated adiabatic passage on oriented nuclei (MAPON) spectroscopy has been used to measure the electric quadrupole interaction at dilute ⁵⁴Mn impurity probes in crystallographically cubic (fcc) cobalt. The measured value is P/h=+5.2(5) kHz and using Q=+0.33(3) b, leads to an electric field gradient of V _zz =+1.3(2)×10¹⁹ V m⁻². This result is consistent with established trends for Mn and Co probes in the 3d ferromagnetic hosts. This revised version was published online in September 2006 with corrections to the Cover Date.     

Orientation dependence of electrical properties of 0.96Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-0.04BaTiO<Subscript>3</Subscript> lead-free piezoelectric single crystal

In this paper, a single crystal of 0.96Na_0.5Bi_0.5TiO₃-0.04BaTiO₃ with dimensions of Φ 30×10 mm was grown by the top-seeded-solution growth method. X-ray powder diffraction results show that the as-grown crystal possesses the rhombohedral perovskite-type structure. The dielectric, piezoelectric and electrical conductivity properties were systematically investigated with 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples. The room-temperature dielectric constants for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples are found to be 650, 740 and 400 at 1 kHz. The (T _m, ε _m) values of the dielectric temperature spectra are almost independent of the crystal orientations; they are (306°C, 3718), (305°C, 3613) and (307°C, 3600) at 1 kHz for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal. The optimum poling conditions were obtained by investigating the piezoelectric constants d ₃₃ as a function of poling temperature and poling electric field. For the 〈001〉 and 〈110〉 crystal samples, the maximum d ₃₃ values of 146 and 117 pC/N are obtained when a poling electric field of 3.5 kV/mm and a poling temperature of 80°C were applied during the poling process. The as-grown 0.96Na_0.5Bi_0.5TiO₃-0.04BaTiO₃ crystal possesses a relatively large dc electrical conductivity, especially at higher temperature, having a value of 1.98×10⁻¹¹ Ω⁻¹⋅m⁻¹ and 3.95×10⁻⁹ Ω⁻¹⋅m⁻¹ at 25°C and 150°C for the 〈001〉 oriented crystal sample.     

Single passage NMRON and the spin-temperature question

The analysis of spin-lattice relaxation (SLR) of very dilute impurity nuclei in ferromagnetic hosts, as encountered in NMR of oriented nuclei (NMRON), usually neglects the spin-spin interaction, assuming a no-spin-temperature model. However, the regime of impurity systems for which this assumption is valid has not been established. the relaxation following single passage in⁶⁰CoFe<110> and⁵⁵CoFe<100> has been measured, and is compared with calculations made with and without a spin-temperature constraint.     

NMRON studies of ferromagnetic hcp and fcc Co

The high resolution hyperfine spectroscopy, modulated adiabatic passage of oriented nuclei (MAPON), has been applied for the first time to high purity, elemental systems. Detailed comparisons between the electric quadrupole hyperfine interactions (EQI’s) and, in particular, their distributions, are obtained for⁶⁰CoCo where the hosts are a single crystal of hcp cobalt and a polycrystalline cobalt foil of predominantly fcc character. For hcp Co, with the electronic magnetization, M, parallel to the c-axis, the mode value P/h=3e²qQ/4I(2I−1)h=−48.5(5) kHz. This fractional distribution implies the sharpest electric field gradient (efg) measured in a metal to date, using MAPON spectroscopy, in excess of two times sharper than that of the most dilute impurity efg in a crystallographically cubic ferromagnetic host. The mode efg is V_zz=−27.3(32)×10¹⁹ Vm⁻². For the polycrystalline, predominantly fcc foil, prepared by quenching, the EQI mode value is P/h=−6.2(4) kHz with a FWHM of 12.0(7) kHz yielding a mode efg of V_zz=−3.5(5)×10¹⁹ Vm⁻².     

Studies of magnetism by nuclear orientation and NMRON

Low temperature nuclear orientation (NO) and nuclear magnetic resonance on oriented nuclei (NMRON) are used to investigate the magnetic properties of solids, and are especially useful when high sensitivity is required, for example in the study of small or dilute systems. Measurement of the static hyperfine interaction and the nuclear spin-lattice and spin-spin relaxation times T ₁ and T ₂ yield information about the electronic magnetization and spin dynamics, respectively. A number of NMRON techniques are available and their application to the study of magnetism will be briefly discussed. In particular, the pulsed technique has been shown to be effective for studying insulators. Recent NO and NMRON measurements, primarily on insulating magnets and magnetic multilayers, will be reviewed. Spins of stable isotopes can also be investigated using NMR thermally detected by NO (NMR-TDNO), and this method, in combination with NMRON, has been recently applied in both metals and insulators to obtain information about nuclear spin-spin couplings, “frequency pulling” and nuclear magnons. This revised version was published online in August 2006 with corrections to the Cover Date.     

The mapon technique and recent developments

Typical linewidths observed in NMRON on dilute impurities in ferromagnetic metals are of order 1 MHz, making difficult the observation of structure in the resonance with splitting Δv much less than this value. The technique of Modulated Adiabatic Passage on Oriented Nuclei (MAPON) was recently developed as a means of measuring the weak electric quadrupole splitting Δv_Q of the nuclear hyperfine interaction due to an electric field gradient V_zz. MAPON has successfully been applied to measure Δv_Q as low as 4 kHz, i.e. less than 0.5% of the inhomogeneously broadened NMRON CWFM resonance line. The isotopes⁵⁶Co,⁵⁷Co,⁵⁸Co and⁶⁰Co have been studied in iron single crystal hosts, yielding Δv_Q consistent with known and estimated quadrupole moments. In addition the results to date give striking confirmation of analyses based on the single impurity relaxation model. Following a brief summary of the theoretical development of MAPON a review of experimental data is given for the CoFe<100> system. The variation of Δv_Q with direction of magnetization, measured in⁵⁸CoFe and⁶⁰CoFe single crystal samples, is also described. Further MAPON measurements are described for a⁵⁶CoFe polycrystalline sample, for which the most probable value and width of the distribution of V_zz can be described simply in terms of the single crystal principal axis results. The application of the MAPON technique to the measurement of nuclear electric quadrupole moments in implanted and diffused samples is discussed.     

Hyperfine Fields of Sr and Y in Ferromagnetic Hosts, and Magnetic Moment of 93Y

Recent studies of hyperfine fields B _HF of Sr and Y in Fe are briefly reviewed. The B _HF value of Y in Ni is given by NMRON of ^91mYNi. The nuclear magnetic moment of the ground state of ⁹³Y is extracted from the β-ray detected NMRON of ⁹³YFe.     

A study of the induced magnetic hyperfine fields in Fe/Ag multilayers

Near perpendicular magnetic hyperfine fields in ^110mAg have been observed in Fe/Ag multilayers. These fields are studied by low temperature nuclear orientation (LTNO) in multilayers [Ag(x ML)/Fe(y ML)]₂₀, with (x,y) monolayer (ML) values of (2,10), (3,9), (5,10) and (3,18). The ^110mAg γ-ray anisotropy was measured as a function of applied magnetic field parallel to the multilayer. The average induced hyperfine field of Ag is significantly influenced by the quality of the multilayer as measured by X-ray diffraction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nuclear moments and optical isotope shifts of108m Ag and110m Ag

The hyperfine structure of the resonance lines of^108m Ag and^110m Ag has been investigated by means of optical interference spectroscopy. The metastable isotopes were produced by neutron irradiation in a reactor. From the measureda- andb-values we derive the value for the nuclear magnetic dipole moment of^108mAgμ _I (108m)=3.577 (20)μ _n and the values for the electric quadrupole momentsQ _I (108m)=1.52(8) bQ _I (110m)=1.65(10) b (without Sternheimer correction). The measured isotope shifts allow the determination of the changes in the mean square charge radii of the nuclei involved:δ 〈r ²〉(108m-107)=0.022(3)fm² δ 〈r ²〉(110m-109)=0.029(2)fm². The isotope positions show odd-even staggering comparable with those of neighbouring isotonic nuclides.     

Discovery of radioactive silver (110mAg) in spiders and other fauna in the terrestrial environment after the meltdown of Fukushima Dai-ichi nuclear power plant

Six months after the explosion of TEPCO’s Fukushima Dai-ichi nuclear power plant, radioactive silver (^110mAg), was detected in concentrations of 3754 Bq/kg in Nephila clavata (the orb-web spider; Joro-gumo in Japanese) collected at Nimaibashi, Iitate village in Fukushima Prefecture, whereas ^110mAg in the soil was 43.1 Bq/kg. A survey of 35 faunal species in the terrestrial environment during the 3.5 years after the accident showed that most of Anthropoda had two orders higher ^110mAg in their tissues than soils, although silver is not an essential element for their life. However, tracing of the activity of ^110mAg detected in spider Atypus karschi collected regularly at a fixed location showed that it declined much faster than the physical half-life. These results suggest that ^110mAg was at once biologically concentrated by faunal species, especially Arthropoda, through food chain. The factors affecting the subsequent rapid decline of ^110mAg concentration in faunal species are discussed.     

NMRON studies of the antiferromagnetic and paramagnetic phases of54Mn-MnCl2 · 4H2O

Pulsed NMRON, CW NMRON and thermal NMR-NO methods have been utilized to study⁵⁴Mn-MnCl₂ · 4H₂O. The⁵⁴Mn spin-lattice relaxation timeT ₁ in zero applied field has been measured between 35 and 90 mK in the antiferromagnetic phase. Above 65 mK the dominant relaxation mechanism is a Raman process with the electronic magnons, but at lower temperatures a direct process takes over. NMRON has been observed for the first time in the paramagnetic phase, and a line width of 300 kHz, with both homogeneous and inhomogeneous contributions, is observed. In the antiferromagnetic phase the line width is 35 kHz, and there are also homogeneous and inhomogeneous contributions. The dependence ofT ₁ for the⁵⁴Mn spins on field and temperature was studied in the paramagnetic phase. AT ₁ minimum centred atB ₀=2.64 T was observed. The hyperfine parameter <⁵⁴ AS>/h=−513.6(3) MHz in the paramagnetic phase, and comparison with the value in the antiferromagnetic phase gives 0.013(1) for the zero point spin deviation.     

Angular distributions of α particles emitted by oriented nuclei and their relation to nuclear deformation

Low-temperature spin orientation of radioactive nuclei is a nuclear spectroscopic method that allows us to obtain experimental data on nuclei and extranuclear fields. We present the results from measuring the angular anisotropy of α radiation emitted by transuranium nuclei of ^253,254Es, ²⁵⁵Fm, ^241,243Am, along with that of γ radiation from ²⁵⁰Bk nuclei oriented in an iron matrix at temperatures of 10–300 mK. The data allow us to establish the relation between the mechanism of α decay and nuclear deformation and to compare them to the theoretical data. We also measure the energy of magnetic hyperfine splitting for the investigated nuclei, and find the magnetic hyperfine field value for Es in Fe to be |B _hf | = 396(32) T. The nuclear magnetic moment for ²⁵⁴Es was determined, and its value was |μ(²⁵⁴Es)| = 4.35(41)μ _N .     

Discrepancies in NMRON Knight Shifts of impurity nuclei in ferromagnets

Precision NMRON field shift studies have been carried out up to 8T on a⁵⁴MnNi single crystal along a hard [100] direction and on a¹²⁵SbFe single crystal along a hard [110] direction. For both systems, high field (B _app>-1T) and low field (0.3T<B _app<0.8T) data sets are obtained. The analysis reveals a significant discrepancy between the apparent Knight Shift dependent on whether the low field or high field data set is utilised. For both systems, consideration of the high field data sets yield a zero Knight Shift K(⁵⁴MnNi)=+0.0(0.2)% and K(¹²⁵SbFe)=+0.2(1.4)%, whereas the low field data sets yield K(⁵⁴MnNi)=+7.5(3.9)% and K(¹²⁵SbFe)=−5.4(3.3)% respectively. The field range dependence of K suggests that only Knight shifts measured in large fields (>-1T) are meaningful for establishing systematics. This casts some doubt on the greater bulk of the literature’s NMRON Knight shift studies, where predominantly low fields have been used to determine K.     

Hyperfine magnetic field of Zn in iron

Precise hyperfine field value of zinc in iron has been determined by nuclear magnetic resonance on oriented nuclei (NMR/ON): B_hf (ZnFe)=−18.785 (35) T at 7 mK. The relaxation constant of Zn in iron is established C_K=14(3) Ks. The new hyperfine field value of zinc in iron allows a more precise reevaluation of the magnetic moments of^69mZn and^71mZn measured with NMR/ON. and the NICOLE Collaboration, CERN     

Study of short-lived bromine isotopes

First experiments in the systematic study of the structure of ground states and isomeric states of Br isotopes as function of neutron number at ISOLDE, CERN are reported. The isotopes^{74g.74m,77,78,84g,84m}Br have been implanted into iron and studied with the techniques of low temperature nuclear orientation and nuclear magnetic resonance of oriented nuclei (NMR/ON). The experiments were performed with the NICOLE on-line nuclear orientation set-up using the isotope separator ISOLDE-3. NMR/ON experiments were successful for^74mBr with continuous on-line implantation and for⁷⁷Br. Using as value of the hyperfine field B_hf(BrFe)=+81.3S (3) T we obtain |g (^74mBr)|=0.455 (3) and |g (⁷⁷Br)|=0.6492 (3). Static nuclear orientation data have been measured for all above mentioned isotopes. From these data we derive |μ(⁷⁸Br, I=1)|=0.13 (3) and |μ(^84gBr, I=2)|=1.9 (7). The results are discussed within the systematics of the bromine isotopes.     

Mössbauer Studies and Magnetic Properties of Y3−x Ce x Fe5O12

It is shown that in-situ ^166mHo (I = 7) in a spherical single crystal of HoF₃ can be used as sensitive internal thermometer to thermally detect NMR (NMR-TDNO) from the 100% abundant stable ¹⁶⁵Ho (I = 7/2) nuclei. In addition, new ^166mHo NMRON results are reported. Both the ^166mHo NMRON and ¹⁶⁵Ho NMR-TDNO spectra show three distinct quadrupolar split sub-resonances, in zero applied field. The data is used to make estimates of the Ho magnetic moments and quadrupole parameters for the ^166mHo and ^166mHo sites.     

Nuclear Orientation Studies of Magnetic Materials

Low temperature nuclear orientation (LTNO) and nuclear magnetic resonance on oriented nuclei (NMRON) can be utilized to investigate the magnetic properties of solids, and are especially useful when high sensitivity is required, for example in the study of small or dilute systems. Spins of stable isotopes can also be studied using NMR thermally detected by NO (NMR-TDNO) of the radioactive nuclei. An effect of nuclear spin coupling in ordered magnets is frequency pulling of the abundant spins, and this has been investigated in the quasi-2-dimensional ferromagnet ⁵⁴Mn–Mn(COOCH₃)₂4H₂O by comparing the NMRON of the dilute radioactive nuclei with the NMR-TDNO of the abundant host nuclei. A structure in the spectra is observed that is yet to be explained. Recent LTNO experiments on magnetic multilayers are described. Experiments implanting radioactive ions into insulating magnets show that the implanted nuclei experience sizeable hyperfine fields, and this may be useful for probing magnetic materials that are difficult to dope by conventional means.     

Magnetic hyperfine field of Hg in nickel and the sign of magnetic moment of 197mAu by NMR-ON

Nuclear magnetic resonance on oriented nuclei (NMR-ON) measurements were performed on the successive decay of ^197mHg–^197mAu in Ni. The NMR-ON resonance spectra of ^197mHgNi were obtained by detecting the 134 keV γ-ray from the decay of ^197mHg and the 279 keV γ-ray from the decay of ^197mAu. The magnetic hyperfine splitting frequency of ^197mHgNi in an external magnetic field of 0.2 T has been determined as 16.55(6) MHz. With the known g-factor of ^197mHg the hyperfine field of B₈₂(^197mHgNi)= -13.53(6) T was deduced. The anisotropy of the 279 keV γ-ray (^197mAu to ¹⁹⁷Au) increased at the resonance. This phenomenon was explained using the spin inversion process including the lifetime of the isomer and the spin–lattice relaxation time. The sign of the g-factor of ^197mAu was determined to be positive. This revised version was published online in August 2006 with corrections to the Cover Date.     

NMRON Study of Magnetically Ordered (166m Ho)HoF3

A NMRON study of magnetically ordered HoF₃ using in-situ neutron activated ^166m Ho (I=7) isoelectronic probes in a spherical single crystal is presented. The optimal sensitivity to resonant change in the gamma-ray anisotropy of the 810 keV daughter gamma-ray emission has been utilised to track the lowest nuclear Zeeman substate resonance over an applied magnetic field range from 0.300 to 0.524 T, corresponding to the frequency range 1.56 to 1.78 GHz. The 2nd lowest substate resonance has also been observed at 0.3 T leading to a value P/h=−32.9(14) MHz for the ^166m Ho quadrupolar splitting which is consistent with predictions of a dominant negative pseudo-quadrupole interaction in this system. The Ho³⁺ electronic moment, in zero applied magnetic field, is projected to be 16% smaller than measured previously with neutron diffraction. This revised version was published online in September 2006 with corrections to the Cover Date.