Magnetic hyperfine fields of Nb andMo in nickel by NMR-ON of90Nb and93mMo

The magnetic hyperfine splitting frequencies of⁹⁰NbNi and^93mMoNi in an external magnetic field of 0.2 T have been determined by the NMR-ON method to be 18.52(7) and23.73(10) MHz, respectively. With the assumption of Knight shift factorK=0 and with the knowng-factors, the hyperfine fields of⁹⁰NbNi and^93mMoNi were deduced asB _HF(⁹⁰NbNi)=-4.118(16) T andB _HF(^93mMoNi)=-3.491(33) T. The rather long spin-lattice relaxation time of 32(5) min was observed for⁹⁰NbNi at an external magnetic field of 0.2T and8 mK.     

Magnetic hyperfine field of arsenic in nickel by NMR/ON of71,72As

The magnetic hyperfine splitting frequencies of⁷¹AsNi and⁷²AsNi in a 0.11 Tesla external magnetic field have been determined by NMR/ON method as 66.00(6) MHz and 106.17(13) MHz respectively. Using the known magnetic moments of μ(⁷¹As)=1.6735(18) and μ(⁷²As)=−2.1566(3), the hyperfine fields were deduced asB _hf(⁷¹AsNi)=12.824(19) Tesla andB _hf(⁷²AsNi)=12.807(16) Tesla.     

Hydrogenation of Zr2Ni

The intermetallic compound Zr₂Ni has been found to take up hydrogen on charging at room temperature. Zr₂(NiFe) H_4.7 and Zr₂(NiFe) H_4.5 show the same structure (CuAl₂ type) as the uncharged compound but with an expanded lattice.Analysis of room temperature spectra in zero and applied fields indicates that the⁵⁷Fe atoms occupy Ni sites in Zr₂(Ni ⁵⁷Fe). Volume expansion effects account for about one third of the increase in isomer shift ( +0.58 mms^–1) observed on hydrogenation. The distribution of hydrogen atoms around the probe³⁷Fe atoms also causes a decrease of 0.23 mms^–1 in the mean value for the quadrupole splitting compared Rith uncharged Zr₂Ni.     

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.     

NMR-ON measurements of187WFe,182,183,186ReNi,186ReFe and203PbFe

The magnetic hyperfine splitting frequencies of¹⁸⁷WFe,¹⁸²Re(j ^π=2⁺)Ni,¹⁸³ReNi,¹⁸⁶ReNi,¹⁸⁶ReFe and²⁰³PbFe in a zero external magnetic field have been determined by the NMR-ON method at about 7 mK as 225.56(6), 130.9(1), 98.17(4), 136.6(4), 1007.0(3) and 58.43(3) MHz, respectively. With the knowng-factors ofg(¹⁸⁶Re, 1⁻)=1.739(3) andg(²⁰³Pb, 5/2⁻)=0.27456(20), the following hyperfine fields were deduced:B _HF(¹⁸⁶ReNi)=−103.05(35) kG;B _HF(¹⁸⁶ReFe)=−759.7(13) kG;B _HF(²⁰³PbFe)=+279.18(25) kG. Taking hyperfine anomalies into account, theg-factor of¹⁸³Re was deduced as |g(¹⁸³Re, 5/2⁺)|=1.267(6). With the assumption of Knight shift factorK=0, theg-factors of¹⁸²Re and¹⁸⁷W and the hyperfine field of¹⁸⁷WFe were determined as |g(¹⁸²Re, 2⁺)|=1.63(5), |g(¹⁸⁷W, 3/2⁻)|=0.414(10) andB _HF(¹⁸⁷WFe) =−714(18) kG. The large hyperfine anomaly was deduced to be¹⁸³W Δ¹⁸⁷W =−0.124(22).     

Critical behavior in radiation damaged systems

Perturbed angular distribution (PAD) measurements of Bleck et al. of the critical behavior of⁶³NiNi,⁶⁶CuNi, and⁶⁷ZnNi have been reanalyzed, and shown to be insufficiently asymptotic to permit deduction of meaningful critical exponents. Via experiments on implanted¹¹¹InNi, done with and without annealing of radiation damage, and by comparison to diffused¹¹¹InNi, it is suggested that unannealed radiation damage can produce serious systematic errors in critical exponents.This work has been supported in part by DMR 01250 from the U.S. National Science Foundation to Clark University, and in part by the Stichting voor Fundamenteel Onderzoek der Materie, the Netherlands     

Pulsed fm NMR/on studies of single crystal54MnNi and125SbFe

Precision field shift studies of B_appl-8T using pulsed FM NMR/ON along hard directions (eg <100>⁵⁴MnNi, <112>¹²⁵SbFe and the easy axis (<111>⁵⁴MnNi, <100>¹²⁵SbFe) yield no measurable Knight shifts within the uncertainty allowed by current accuracy of the nuclear moments. This is in striking contrast to earlier measurements with the same apparatus that yielded K=+1.5 (4)% for⁶⁰CoFe. The modulation frequency dependences of the pulsed FMNMR/ON signals are investigated for a variety of rf parameters and compared with model predictions.     

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 EQI's. 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.     

Magnetic hyperfine fields of Zr in nickel and iron measured by the DPAD method

The magnetic hyperfine fields of Zr in nickel and iron were measured by the DPAD method. Using the 8⁺ isomeric states in⁹⁰Zr and⁸⁸Zr these fields were found to beH _hf(ZrNi)=–4.65(10) T andH _hf(ZrFe)=–27.4(4) T, respectively.     

Hyperfine magnetic fields at rare-earth elements in ferromagnetic transition metals

Hyperfine magnetic fields for such probes as:¹⁵²SmFe,¹⁵²SmCo,¹⁵²SmNi,¹⁵⁵GdFe,¹⁷²YbFe,¹⁷²YbCo and¹⁷²YbNi have been measured using PAC method. The quantitative analysis of components of these fields has been also performed.     

Critical exponentβ for hyperfine fields in nickel

The magnetic hyperfine fields for⁶³Ni,⁶⁶Cu, and⁶⁷Zn nuclei in nickel metal have been measured by means of perturbed-ray angular distribution techniques at different temperatures up to 1 K below the Curie temperature,T _C . The temperature dependence of the fields can be very well fitted by (1—T/T _C ) with best values=0.322(16) for⁶³NiNi, = 0.427(42) for⁶⁶CuNi, and=0.427(14) for⁶⁷ZnNi respectively. The differences between these exponents indicate that there could be probe atom dependent deviations from proportionality between hyperfine field and bulk magnetization in the critical region.Work performed in partial fulfillment of the requirements for a doctorate in physics at the Freie Universität, Berlin     

Mapon and single passage NMRON spectroscopy on125SbFe and125SbNi single crystals

The signs, mode magnitudes and distributions of the electric quadrupole hyperfine interactions (EQI) in single crystal¹²⁵SbFe and¹²⁵SbNi have been examined along a principal hard axis for each system and are compared with earlier easy axis results. The surface preparation was essentially the same for both hosts but the results of the distribution width and anisotropy in the mode values of the measured EQI’s are remarkably different between the two hosts. For¹²⁵SbFe the mode value of the EQI is a factor of two larger along the hard axis <111> and the same sign, negative, as for the easy axis <100>. For¹²⁵SbNi the mode values of the EQI along the same two principal directions are comparable in magnitude but the efg distributions are much broader than in the¹²⁵SbFe case. Single passage results on¹²⁵SbNi provide a weak sweep asymmetry with indications of an apparent change in sign in EQI from negative along the <111> easy axis to positive along the hard <100> axis.     

Hyperfine field at strontium nuclei in nickel

The hyperfine field H_hf for SrNi has been measured by the TDPAD method using recoil implantation of an 8⁺ isomer of⁸⁶Sr in Ni following heavy ion reactions. Two fieldsites populated about equally with H_hf(1)=–38.6(18) kOe and H_hf(2)=–54.2(11) kOe have been observed. These field values are well explained by conduction electron polarization alone.Supported by the National Science Foundation.     

The magnetic hyperfine field at181Ta impurities in the 4f-ferromagnets Ho and Er

The magnetic hyperfine fieldH _hf at¹⁸¹Ta impurities in the ferromagnetic Rare Earth metals Ho and Er has been determined by time differential perturbed angular correlation measurements at 4.2 K. The results |H _hf(TaHo)|=101(8)kG |H _hf(TaEr)|= 94(8)kG together with the previously determined values ofH _hf(TaGd) andH _hf(TaDy) show that the magnetic hyperfine field at Ta impurities in the Rare Earth metals is predominantly due to the conduction electron polarization of the hosts.     

g-factor of the 9/2+ isomeric state in 65Ni from transfer reaction

We report a measurement of the g-factor of the I ^π = 9/2⁺, t _1/2 = 22ns isomer in ⁶⁵Ni. The state of interest was populated and spin-oriented using a single-neutron transfer on an enriched ⁶⁴Ni target. The value, which was obtained, g(9/2⁺,^65m Ni) = - 0.296(3) is well in agreement with the g-factors of the other 9/2⁺ states in the region and with large-basis shell model calculations. The known g-factor of the 9/2⁺ isomer in ⁶³Ni was used in order to verify the strength of the hyperfine field of Ni( Ni) at room temperature.     

Recent experiments with transient NMRON

High resolution magnetic and electric hyperfine interaction distributions are determined for single crystal⁵⁴MnNi with diffused impurity concentrations of 0.14 and 0.40 at%, and for a 0.1 µm layer of⁶⁰CoFe co-plated onto single crystal Fe. High quality gamma detected nuclear spin echoes recorded for the⁶⁰CoFe specimen demonstrate that a reduced influence of the RF skin effect far outweighs any magnetic hyperfine field interaction broadening associated with the co-plating process.     

Magnetic hyperfine field of Se in nickel measured by means of the DPAC method

The magnetic hyperfine field of Se in nickel was measured by means of the time-differential perturbed angular correlation (DPAC) technique, using the 755–250 keV γ-ray cascade fed in the decay of⁷⁷Br. A value ofB _hf(NiSe)=+15.11(35) T was obtained at room temperature. The half-life of the 250 keV state and the anisotropy of the 755–250 keV cascade were found to beT _1/2=9.68(6) ns andA ₂₂=−0.454(9), respectively.     

NMR/ON of206Bi implanted at T < 0.2 K and at room temperature into nickel

NMR/ON has been observed for²⁰⁶BiNi with samples prepared by implantation at T<0.2 K and at room temperature. The integrated destruction of anisotropy for the sample implanted at 290 K is only about half of that for the on-line implanted sample but the resonance line is less broad and has a narrow component with centre frequency _L= 223.62(10) MHz for zero external field. With the known g-factor of²⁰⁶Bi we derive from this frequency the hyperfine field of BiNi as B_hf=38.3(4) T.     

Hyperfine interactions of light Ir,Re isotopes in iron

The technique of On-line Nuclear Orientation has been applied to light Ir and Re isotopes. Using both¹⁹²IrFe and⁵⁴MnNi thermometers, orientation as a function of temperature was measured over the range 10–100 mK. Pulsed implantation methods were used to obtain spectra with gamma transitions well identified and clear of contaminant activities. Magnetic moment/oriented state spin combinations were obtained for^180,182,183Ir and for^180,179Re. The results are briefly discussed.     

Quadrupole interaction studies of Hg in Sb

Time differential perturbed angular correlation and nuclear orientation studies of the electric quadrupole interaction for Hg in Sb have been performed. The effective field gradients |V _zz ^eff (HgSb)|=1.43(18)×10¹⁷V cm^–2 at room temperature andV _zz ^eff (HgSb)=+1.8(2) × 10¹⁷V cm^–2 below 0.05 K have been derived. These two values are no indication for an anomalous temperature dependence of the effective field gradient for Hg in Sb. The value of the electric field gradient fits well into the systematics for Hg in other hosts. It is shown that the electronic enhancements of the field gradients are correlated to the valence of the impurities and are rather insensitive to the host properties.On leave of absence from: University of Lisboa, Portugal