The temperature dependence of the magnetic hyperfine field of tantalum in dysprosium

The temperature dependence of the magnetic and electric hyperfine interactions at the site of ¹⁸¹Ta impurities in polycrystalline Dy has been measured between 4.2 and 178 K using the time differential perturbed angular correlation technique. The value of the magnetic hyperfine field at 4.2 K is: |H_hf(TaDy)| = 212(9) kG The temperature dependence of the magnetic hyperfine field follows closely the prediction of the molecular field model.     

Low temperature pressure dependence of the muon hyperfine fields in iron,cobalt and nickel

The pressure dependence of the μ⁺ local magnetic fields in polycrystalline Fe and Ni and a Co single crystal has been measured at 77 K, up to 0.7 GPa, using a He gas high pressure setup. The pressure derivatives dlnB_μ/dP in units of mT/GPa are +4.4±1.0 (Fe), -0.7±1.1 (Co) and +0.63±0.10 (Ni). From these values the hyperfine field volume derivatives are deduced. Using these values together with previously determined room temperature derivatives the thermal expansion part of the temperature dependence of the hyperfine field can be calculated. The remaining explicit temperature dependence below 300 K, which deviates markedly from the temperature dependence of the bulk magnetization, is discussed.     

Study of combined magnetic and electric hyperfine interactions for cadmium in Dysprosium by time differential perturbed angular correlations

The combined magnetic and electric hyperfine interaction at the site of a¹¹¹Cd impurity in magnetically ordered Dysprosium has been investigated as a function of temperature by time differential perturbed angular correlation measurements. Three different phases have been found in metallic Dy with transition temperatures of 85 and 179 °K in agreement with the results of bulk material measurements. In the paramagnetic phase above 179 °K a pure electric quadrupole interaction has been observed. The various contributions to the electric fieldgradient are analyzed and it is shown, that the dominant contribution comes from the conduction electrons. In the ferromagnetic phase which extends from 0 to 85 °K the magnetic hyperfine field at the site of¹¹¹Cd has the same temperature dependence as the spontaneous magnetization. The value of the hyperfine field at 4.2 °K is ¦H _eff¦=(221 ± 4) kG. At 85 °K a transition to the antiferromagnetic phase of Dy occurs, which shows a hysteresis of the transition temperature. In the antiferromagnetic phase the temperature dependence of the hyperfine field deviates considerably from the magnetization curve. It is suggested that this deviation might be due to a temperature dependence of thes-f exchange interaction.     

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 (B_hf) 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 B_hf does not show any signature of ferromagnetic ordering, but is reminiscent of enhanced paramagnetism.     

Hyperfine Interactions of Pm in Nd and Gd Hosts

Time differential perturbed angular correlation measurements were carried out using short lived isomeric 5/2⁺ state in ¹⁴⁷Pm to investigate the magnetic and electric hyperfine interactions in Nd and Gd hosts at different temperatures. At 10 K the magnetic hyperfine fields at ¹⁴⁷Pm in Nd and Gd hosts are 361(42) kG and 256(30) kG, respectively, and are very low as compared to the free-ion value while the electric field gradients are of comparable order. The magnetic hyperfine field in Gd is constant with temperature. The results are interpreted in terms of singlet ground state of Pm ion. This revised version was published online in September 2006 with corrections to the Cover Date.     

Derg-Faktor des 364 keV-Zustandes von184W und die Hyperfeinfelder von Wolfram in Eisen,Kobalt und Nickel

Theg-factor of the 364 keV state of¹⁸⁴W was measured by the time integral angular correlation method using the high hyperfine fields at the tungsten nucleus in iron. The same experiment was performed with the 111 keV state giving the ratiog(364 keV)/g(111 keV)=1.02(14). Using this ratiog(364 keV-level)=0.286(35) was deduced. For the hyperfine fields of W in Fe, W in Co and W in Ni at 300 K ?610(35) kG, ? 358(23) kG and ?80(3) kG respective have been determined.     

TDPAD measurements of magnetic hyperfine field for <Superscript>132</Superscript>Ba in ferromagnetic Ni

The magnetic hyperfine field of Ba in ferromagnetic Ni has been measured by time differential perturbed angular distribution technique using the 13 ns 10⁺ isomeric state in ¹³²Ba as probe which was populated in the reaction ¹²C(¹²⁴Sn, 4n) ¹³²Ba at beam energy of 60 MeV. The hyperfine field extracted from the observed Larmor precession frequency comes out to be ?84(5) kG. Our experimental results show good agreement with theoretical calculations performed within local density approximation of the density functional theory. The hyperfine field data presented here would be useful towards accurate determination of g-factor in other high spin states in Ba isotopes.     

The magnetic hyperfine field at Cd nuclei in the rare earth ferromagnets Gd,Tb, Dy,Ho, Er and Tm

The time differential perturbed angular correlation technique has been used to study the combined magnetic and electric hyperfine interactions at the site of a¹¹¹Cd impurity in the rare earth ferromagnets Gd, Tb, Dy, Ho, Er, and Tm at 4.2 °K. The following magnetic hyperfine fields at the site of¹¹¹Cd have been found: ¦H _hf ¦=340(7) kG in Gd, 275 (5) kG in Tb, 221 (4) kG in Dy, 116 (3) kG in Er and 60 (6) kG in Tm. In Ho two magnetically different sites were observed with magnetic fields of 159 (3) and 139 (3) kG. Both sites are equally populated. The coupling constantJ _5f of the conduction electron-4f interaction has been calculated for the different rare earth metals from the measured hyperfine fields by means of the RKKY theory.     

Nuclear magnetic resonance on oriented189,191 Pt in iron

Nuclear magnetic resonance measurements have been performed for¹⁸⁹Pt and¹⁹¹Pt oriented at 7 and 15 mk in iron host. The magnetic hyperfine splitting frequencies, ν=¦μB_HF/Ih¦, of the¹⁸⁹Pt and¹⁹¹Pt ground states were determined to be 277.61(5) and 319.88(3) MHz. With the hyperfine field of B_HF=-1280(26) kG the nuclear magnetic moments were deduced to be: ¦μ(¹⁸⁹Pt;3/2^?)¦=0.427(9) μ^N; ¦μ(¹⁹¹Pt,3/2^?) ¦=0.492(10) μ_N. The effective spinlattice relaxation time for¹⁹¹PtFe at 7 mK in a polarizing magnetic field of 2 kG has been found to be 30(2) s using a single-exponential fit.     

The hyperfine field on carbon in iron

Integral perturbed angular correlation experiments have been carried out on recoilimplanted¹⁵C nuclei in iron. The 739 keV5/2⁺ level of¹⁵C was populated via the¹⁴C(d, p)¹⁵C^* reaction. Using the known g-factor and lifetime of the state, effective internal fields of –12.4±1.1 kG and –10.9±1.5 kG were determined at room temperature and 77 K, respectively. A conduction electron polarization hyperfine field of about –20 kG was deduced from the data.Work supported in part by the National Science Foundation.     

Temperature dependence of the positive-muon knight shift in MnSi

The temperature dependence of the μ⁺ Knight shift in weakly-helimagnetic MnSi has been measured in the temperature range between 28 and 300 K. The observed shift is found to be directly proportional to the host susceptibility in the paramagnetic state with a hyperfine coupling constant of —4.8 kOe/_μB.     

Nuclear magnetic resonance on oriented192Ir in Fe and Ni

The hyperfine interaction of¹⁹²Ir nuclei as dilute impurities in Fe and Ni has been investigated with NMR on oriented nuclei. With the use of highly dilute and pure alloys the line widths could be reduced so far that the quadrupole splitting of¹⁹²IrFe and¹⁹²IrNi could be resolved. Taking hyperfine anomalies into account the ground state nuclear moments of¹⁹²Ir are deduced as |μ|=1.924(10)μ _N andQ=2.36(ll) b. The hyperfine field of IrNi was investigated as a function of the Ir concentrationc between 0.01 at % and 5 at %. The dependence ofH _HF onc was found to be significantly smaller than that reported from Mössbauer effect measurements. Forc=0.01 at %H _HF=?454.7(2.3)kG is deduced. The resonance shift with an external magnetic field has been studied precisely, yieldingK=0.012(23) andK=0.026(12) for the Knight-shift of¹⁹²Ir in Fe and Ni, respectively.     

Muon hyperfine fields in iron and its dilute alloys

The temperature dependence (240 to 633 K) of the interstitial magnetic field, B_μ, as determined by the rotation of the spin of the μ⁺, has been measured for dilute polycrystalline iron alloys with Mo, Ti and Nb additions. In all cases the behaviours differ from one another and from the Fe(A1) alloys previously studied. B_μ, which is negative with respect to the magnetization, is increased in magnitude by A1 and Mo, and decreased greatly by Ti. The addition of Nb creates a two- phase alloy from which we can assess the role of heterogeneity and/or strain on B_μ in iron. If the temperature dependence of the hyperfine field B_hf extracted from B_μ for Fe(Mo) alloys is interpreted on the model previously used to discuss the Fe(A1) data, we would conclude that the muon is attracted to the Mo atom while repelled by the A1 atoms as the temperature decreases. Measurements giving room temperature values of B_μ for iron alloys with Mn, Cr, V and W taken after annealing above the recrystallization temperature are also reported.     

Interactions of μAl acceptor impurity in weakly and heavily doped silicon

The interactions of the aluminum acceptor impurity in silicon are investigated using polarized negative muons. The polarization of negative muons is studied as a function of temperature on crystalline silicon samples with phosphorus (1.6×10¹³ cm^?3) and boron (4.1×10¹⁸ cm^?3) impurities. The measurements are performed in a magnetic field of 4.1 kG perpendicular to the muon spin, in the temperature range from 4 to 300 K. The experimental results show that, in phosphorus-doped n-type silicon, an _μAl acceptor center is ionized in the temperature range T>50 K. For boron-doped silicon, the temperature dependence of the shift of the muon spin precession frequency is found to deviate from the 1/T Curie law in the temperature range T ? 50 K. The interactions of a _μAl acceptor that may be responsible for the effects observed in the experiment are analyzed.     

27Al pulsed nuclear magnetic resonance study of CeAl2

The magnetic properties and the electronic structures of a rare-earth aluminum intermetallic compound CeAl₂ are investigated by magnetic susceptibility measurements and ²⁷Al pulsed nuclear magnetic resonance (NMR) techniques. The magnetic susceptibility is strongly temperature-dependent, following a Curie–Weiss law down to ∼12 K, and shows an antiferromagnetic transition at 4 K. The ²⁷Al NMR spectra show a typical powder pattern for a nuclear spin I of 5/2 with the second-order nuclear quadrupole interaction at high temperature and an additional large dipolar broadening between the 4f electron spins of cerium and the ²⁷Al nuclear spins at low temperature. The ²⁷Al NMR Knight shift follows the same temperature dependence as the magnetic susceptibility, suggesting that the ²⁷Al NMR Knight shift originates from the transferred hyperfine field of the Ce 4f electron spins with the hyperfine coupling constant of A = +5.7 kOe/μ_B. The spin-lattice relaxation rate 1/T₁ is roughly proportional to temperature, as with most non-magnetic metals at high temperature, and then strongly temperature-dependent, increasing rapidly with a peak near the antiferromagnetic transition temperature and decreasing at lower temperature. The temperature dependence of the Korringa ratio K, however, suggests that the antiferromagnetic spin fluctuation signature, which is an enhancement in the Korringa ratio, is washed out owing to the geometrical cancellation of Ce 4f fluctuations at the Al sites.     

Anomalous field dependence of muon Knight shift and line width in the singlet ground state compound PrCu2

We report on ZF and TF‐studies of PrCu₂ above the induced Jahn–Teller transition at 7.3 K. Generally a two‐component signal is found, one showing inhomogeneous the other one homogeneous, temperature dependent line broadening. In ZF the former component is well represented by a Gaussian Kubo–Toyabe function with \varDelta \simeq 6.5\,μs^-1 at 7.5 K, corresponding to a field width of 76 G. This is about 30 times larger than what is calculated to arise from the ¹⁴¹Pr‐nuclear dipole moments alone, pointing to strong hyperfine enhanced features. TF‐field scans at 12 K revealed that the enhancement is suppressed in external fields exceeding 1 kG. In parallel the Knight shift drops from very large values well above 10% at 100 G to shifts of the order of 1% above 1 kG. A scaling of the Knight shifts with the corresponding relaxation rates seems to imply that the strange field dependence below 1 kG is associated with the magnetic susceptibility of the muons’s nearest neighbour Pr³⁺‐ions, a result for which we have no explanation yet to offer. This revised version was published online in July 2006 with corrections to the Cover Date.     

Die Hyperfeinstruktur des 32P3/2-Zustands von Natrium im starken Magnetfeld

The hyperfine structure of the 3²P_3/2 State of Na²³has been measured by the optical double resonance technique in a magnetic field of 3.1 kG sufficiently strong to decouple completelyI andJ. In the case of π or (σ⁺+σ^?) excitation the double resonance signal represents the superposition curve of eight unresolved radio-frequency transitions. The dependence of the signal on the pressure of sodium vapour and the radio-frequency field strength has been studied. The analysis of the experimental curves yields for the hyperfine coupling constants the valuesa=(18.7±0.4) Mc/s andb=(3.4±0.4) Mc/s. The nuclear electric quadrupole moment derived from the ratio ofb/a isQ=(0.146±0.02) · 10^?24cm². The Lande factor and the lifetime for the 3²P_3/2state are g_J=1.3344±0.0004 and τ=(1.61±0.07) · 10^?8 sec.     

Antiferromagnetism in57Co-doped La2CuO4−y studied by Mössbauer spectroscopy

Mössbauer effect studies of⁵⁷Co-doped La₂CuO_4?y were performed at temperatures between 4.2 K and room temperature. These confirm the antiferromagnetic ordering of these compounds below room temperature. Temperature dependence of the quadrupole splitting shows that the hyperfine field is at an angle with thec-axis.     

Perturbed angular distribution of recoil implanted19F-nuclei in a cobalt and copper environment

The magnetic hyperfine field acting on¹⁹F nuclei in a cubic cobalt lattice at a temperature of 450 °C has been investigated. Time dependent spin rotation has been observed following the excitation and recoil implantation with a pulsed α-particle beam using the reaction¹⁹F(α,α′)¹⁹F*. The hyperfine field isH _hf (450 °C)=31.4 ± 0.5 kG. The measured amplitude of the spin rotation is only 18% of the amplitude expected for the case where all¹⁹F* nuclei are assumed to be subject to the same hyperfine field without any further perturbation. This was established by means of other implantation experiments with a copper backing using first the pulsed beam technique followed by a γ-ray angular distribution measurement in coincidence with backscattered α-particles. In copper a fast perturbation was found, which reduces the anisotropy to about 80% within a short time interval immediately after the excitation.     

Theg-factor of the 9/2+ [624] ground state of183Os

The hyperfine interaction of¹⁸³OsFe has been studied with nuclear magnetic resonance on oriented nuclei after recoil implantation. Taking into account the resonance displacement due to quadrupole interaction |gμ _N H _HF/h|=149.9(2) MHz has been found. WithH _HF=?1,115(20) kG theg-factor of the 9/2⁺ [624] ground state of¹⁸³Os is deduced asg=(?)0.176(3).