D. H. Chaplin

Recent experiments with mapon spectroscopy

Electric quadrupole interactions of impurity nuclei in single crystals of54MnNi,125SbNi and125SbFe have been studied as a function of crystal field direction and applied magnetic field using MAPON. Distributions are in all cases broad compared with the mode values of the EQIs. For54MnNi the mode efg is isotropic to better than 5% between the easy <111> axis and a hard <100> axis. The efg is +0.88 (15)x 1019 Vm−2. The mode efg for125SbFe along its easy <100> axis is one half of that along a hard <112> axis, and one third of that measured along the easy <111> axis of125SbNi. The much larger efg mode and distribution seen in125SbNi, for four to eight times greater dilution than for125SbFe, suggests intrinsic contributions due to valence screening effects in the more itinerant nickel host.

Nuclear magnetic resonance of thermally oriented nuclei

The more recent developments in the spectroscopy of Nuclear Magnetic Resonance on Oriented Nuclei (NMRON) are reviewed; both theoretical and experimental advances are summarised with applications to On-Line and Off-Line determination of magnetic dipole and electric quadrupole hyperfine parameters. Some emphasis is provided on solid state considerations with indications of where likely enhancements in technique will lead in conventional hyperfine studies.

Nuclear orientation — Pulsed magnetic resonance studies of60Co nuclei in iron

The observation of nuclear magnetic resonance of oriented60Co nuclei in iron using the techniques of pulsed single passages and single unswept radiofrequency pulses is reported. For large rf fields resonant destructions as high as 80% of the γ-radiation anisotropy were observed.

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 (Bapp>-1T) and low field (0.3T<Bapp<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.

Nuclear magnetic resonance of brute force oriented110mAgAg

NMR on brute force oriented nuclei (NMRON/BF) has been observed for110mAg 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 the110mAg moment of μ=3.589(4) nm (uncorrected). Factors pertinent to successful NMRON/BF in systems such as110mAgAg, with a complex decay scheme and modestg-factor, are also discussed.

Multistructural character of nuclear spin echo signals formed from multidomain ferromagnets: theory and experiment

The formation of multiple, non-quadrupolar, spin echo signals from multidomain ferromagnets is extensively studied both theoretically and experimentally, providing for the first time the fundamental understanding of this complex structure.

MAPON spectroscopy and its application to transition metal ferromagnets

Modulated adiabatic passage on oriented nuclei (MAPON) is a technique developed specifically to measure very small electric quadrupole interactions (EQIs) at radioactive probe nuclei even when such interactions are masked in the frequency domain by inhomogeneous magnetic broadening associated with a dominant magnetic hyperfine interaction. In this paper an overview of the technique is presented with particular reference to 60CoCo EQI measurements which were an important step in establishing MAPON methodology. MAPON results for dilute nd impurities in ferromagnetic Fe and Ni metal hosts are reviewed including presentation of new data for 58CoNi and 60CoNi. Priorities for future studies are provided on the basis of this review.

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 Vzz=−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 Vzz=−3.5(5)×1019 Vm−2.

Transient NMRON of brute force oriented110mAgAg

A novel technique involving electrodeposition has been used to prepare an elemental silver specimen wherein radioactive110mAg probe nuclei are confined to a surface layer of approximately 0.1 μm depth. This specimen was then brute force oriented in a field of 8T and the continuous wave (CW) nuclear magnetic resonance on oriented nuclei (NMRON) spectrum showed an integrated destruction of some 58%. Moreover the transient NMRON techniques of single and modulated adiabatic passage were successfully applied, resulting in a determination of the electric quadrupole interaction strength at the110mAg site in polycrystalline silver of P/h=+0.74(5)kHz with a FWHM of ΔP/h=0.75(8)kHz. The resulting mode electric field gradient is Vzz=+1.87(23)×1018Vm−1. Analysis of the single passage data provides an estimate for the nuclear spin lattice relaxation constant in silver at 8T of Ck=1.6(3)s.K.

Theory of spin-echo nuclear orientation magnetic resonance experiments

A theoretical treatment of the radiative detection of three-pulse spin-echo magnetic resonance of oriented nuclei is given. The relationship of the echo shapes to the Fourier transform of the lineshape function is discussed. Conditions for the experimental observation of the main and harmonic echoes are determined.