Anomalous temperature dependence of the 1.7T magnetic hyperfine field of fluorine in nickel

By means of time-differential perturbed angular distribution (TDPAD) techniques, the magnetic hyperfine field ofF atoms implanted in a ferromagnetic Ni lattice has been measured at temperatures from 80 K to 650 K obtaining, for example, a fieldH ₁(295 K)=+1.72(3)T at room temperature. The temperature dependence of the reduced fieldH ₁(T)/H ₁(0) has been found to deviate up to 38% from that of the reduced magnetization of the Ni host. Comparing this result for the halogenF with other nontransitional impurities in nickel, it seems that such deviations become more pronounced with increasing number of excessp-electrons of the impurity. With a simple two-zone model distinguishing between the hyperfine fields originating in the local and in the more distant undisturbed surrounding of theF impurity, the observed temperature dependence can be explained. In this approach the disturbed magnetization of the inner zone is described by localized Ni moments in the molecular field approximation.A satellite magnetic field of + 9.4T was observed at 80 K only.Supported by the Bundesministerium für Forschung und Technologie     

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.     

The temperature dependence of the57Fe hyperfine magnetic field distribution in Fe-Ni

The temperature dependence of the⁵⁷Fe hyperfine magnetic field (hmf) in Fe-Ni is stronger than the temperature dependence of the⁵⁷Fe hmf in pure Fe. By analyzing the shape of the⁵⁷Fe hmf distribution, and with the help of experiments with Si in Fe-Ni, we deduce that this anomalous temperature dependence originates from a large thermal sensitivity of the magnetic moments at those Fe atoms with more Ni nearest neighbors. A strong temperature dependence of the recoilfree fraction was also observed in Fe-Ni alloys. We suggest that a large mean square thermal displacement of Fe atoms in Fe-Ni is the cause of the anomalous temperature dependence.     

Anomalous temperature dependence of the magnetic field penetration depth in superconducting UBe13

We report the first measurements of the magnetic-field penetration depth in the heavy electron superconductor UBe₁₃, performed using a SQUID magnetometer. We find the temperature dependence of (T)-(0) to follow aT ² law at low temperatures, giving further evidence of extreme gap anisotropy in this compound. We calculate the temperature dependence expected for a variety of anisotropic states, including those representing certain classes of exotic pairing. In general situations, the supercurrent is not parallel to the vector potential, and a more complicated field penetration takes the place of the normal Meissner effect. We argue that the data are consistent with an energy gap with point nodes on the Fermi surface but inconsistent with the large value of the Landau parameterF ₁ ^S expected for a translationally invariant Fermi liquid with large effective mass.     

Anomalous absorption of ultrasound in gadolinium in a magnetic field

The absorption coefficient α _k for longitudinal ultrasonic (15 MHz) waves propagating transverse to the direction of a magnetic field H is measured in single crystal gadolinium. It is found that in fields H⩽600 Oe, the peak in α _k is shifted toward lower temperatures, while the absolute magnitude of the absorption rises with increasing H. It is shown on the basis of dynamic scaling that the anomalous behavior of α _k in fields H⩽600 Oe can be explained by introducing a magnetic field analog of the Landau-Khalatnikov relaxation mechanism. Fiz. Tverd. Tela (St. Petersburg) 39, 339–340 (February 1997)     

Anomalous temperature dependence of resistivity in quasi-one-dimensional conductors in a strong magnetic field

We present a heuristic, semiphenomenological model of the anomalous temperature (T) dependence of resistivity recently observed experimentally in the quasi-one-dimensional (Q1D) organic conductors of the family in moderately strong magnetic fields. We suggest that a Q1D conductor behaves like an insulator (), when its effective dimensionality is one, and like a metal (), when its effective dimensionality is greater than one. Applying a magnetic field reduces the effective dimensionality of the system and switches the temperature dependence of resistivity between the insulating and metallic laws depending on the magnitude and orientation of the magnetic field. We critically analyze whether various microscopic models suggested in literature can produce such a behavior and find that none of the models is fully satisfactory. In particular, we perform detailed analytical and numerical calculations within the scenario of magnetic-field-induced spin-density-wave precursor effect suggested by Gor'kov and find that the theoretical results do not agree with the experimental observations. Received 20 October 1998     

Temperature dependence of the magnetic hyperfine field at cerium impurity in Co

Perturbed gamma-gamma angular correlation (PAC) technique was used to measure the magnetic hyperfine field (B _hf ) at Ce impurity in Co using ¹⁴⁰La→ ¹⁴⁰Ce probe. The radioactive ¹⁴⁰La produced by neutron irradiation of lanthanum metal with thermal neutrons was introduced in Co by arc melting in argon atmosphere. The present measurements cover the temperature range from 4.2– 1300 K. Two pure magnetic interactions were observed at impurity sites, corresponding to a ferromagnetic ordering of Co moments in hcp and fcc phases. The temperature dependence of B _hf for both phases, however, shows a sharp deviation from an expected standard Brillouin-like behavior for the host magnetization. The results are discussed in terms of a simple molecular-field model where the localized moment at impurity ions as well as the conduction electron contributions to the hyperfine field are taken into account.     

The temperature dependence of the hyperfine interaction of the transition metal osmium in a gadolinium host matrix

Integral perturbed angular correlations of the 931-155keVγγ-cascade of¹⁸⁸Os in Gd have been measured. With this technique the combined magnetic and electric hyperfine interaction of the 155 keV level of¹⁸⁸Os as an impurity in a Gd host has been studied as a function of temperature. The result for the electric field gradient of Os in Gd at 300 K is: $$\left| {V_{zz} \left( {Os:\underline {Gd} } \right)} \right| = \left( {12.8_{ - 1.9}^{ + 3.1} } \right) \cdot 10^{17} {V \mathord{\left/ {\vphantom {V {cm^2 }}} \right. \kern-\nulldelimiterspace} {cm^2 }}.$$ For the magnetic hyperfine field at 4.2 K the value $$H_{hf} \left( {Os:\underline {Gd} } \right) = - 134\left( {26} \right)kG$$ was obtained. Sign and magnitude of the magnetic hyperfine field suggest the existence of a localized moment of about ?0.4 µ _B at the site of Os in Gd. With increasing temperature the magnetic hyperfine field decreases much stronger than the magnetization of the host. Possible explanations for this anomalous temperature dependence are discussed.     

Anomalous temperature dependence of the magnetic field induced antiferromagnetic moment in the antiferroquadrupolar ordered state of CeB6

The magnetic field induced antiferromagnetic moment M(AF) at low magnetic fields in the antiferroquadrupolar (AFQ) ordered phase of CeB6 was investigated by elastic neutron diffraction experiments for H parallel [110]. The peak intensity at the AF magnetic reciprocal point (1 / 2,1 / 2,1 / 2) corresponding to M(2)(AF) increases with decreasing temperature below the AFQ ordering temperature T(Q), and exhibits a broad maximum at T approximately 3 K and decreases with a further decrease of temperature. This unusual behavior of M(AF) at low fields is explained as a result of the competition between the AF-octupolar and AF-exchange interactions in the O(xy) type AFQ ordered state.     

Absence of magnetic hyperfine field on 99Ru in chromium

The dilute impurity hyperfine field on ruthenium nuclei in a chromium matrix has been measured to be zero in the temperature range 2.3–330 K using the time-differential perturbed angular correlation technique. Possible mechanisms responsible for the observed result are discussed.     

The hyperfine field of99Tc in iron

The magnetic hyperfine field at⁹⁹Tc impurities in Fe has been measured to be ¦H _hf¦=325 (7) kGauss at 298 °K. The technique of time-differential perturbed angular correlations on the 181 keV state of⁹⁹Tc was used.     

Spin and temperature dependence of the magnetic hyperfine field of Cd in the rare earth-aluminum Lavesphase compounds RAl2

Perturbed angular correlation spectroscopy has been used to investigate the combined magnetic and electric hyperfine interaction of the probe nucleus ¹¹¹Cd in ferromagnetically ordered rare earth (R)-dialuminides RAl₂ as a function of temperature for the rare earth constituents R=Pr, Nd, Sm, Eu, Tb, Dy, Ho and Er. In compounds with two magnetically non-equivalent Al sites (R=Sm, Tb, Ho, Er), the magnetic hyperfine field was found to be strongly anisotropic. This anisotropy is much greater than the anisotropic dipolar fields, suggesting a contribution of the anisotropic 4f-electron density to magnetic hyperfine field at the closed-shell probe nucleus. The spin dependence of the magnetic hyperfine field reflects a decrease of the effective exchange parameter of the indirect coupling with increasing R atomic number. For the compounds with the R constituents R=Pr, Nd, Tb, Dy and Ho the parameters B₄, B₆ of the interaction of the crystal field interaction have been determined from the temperature dependence of the magnetic hyperfine field. The ¹¹¹Cd PAC spectrum of EuAl₂ at 9 K confirms the antiferromagnetic structure of this compound.     

Ratio ofg I -factors and hyperfine structure anomalies of99Ru and101Ru

The ratio of theg _I -factors of⁹⁹Ru and¹⁰¹Ru has been measured accurately by the nuclear magnetic resonance method. Using hyperfine interaction constants from literature, the hyperfine structure anomalies of some atomic states of ruthenium are obtained.     

The radial dependence of the magnetic hyperfine field for Sn atoms in the ferromagnetic Heusler alloys

The magnetic hyperfine fields,B _hf, for impurity¹¹⁹Sn atoms in Z sites of ferromagnetic Heusler alloys Co₂MnZ (Z=Si, Ge) are measured by the Mössbauer effect. At 77 KB _hf=–1.43±0.04 T in Co₂MnSi andB _hf=+1.05±0.05 T in Co₂MnGe. From the comparison between the values ofB _hf for Sn atoms in Co₂MnZ (Z=Si, Ge, Sn), it follows that the negative contribution toB _hf drops as the interatomic distance begins to increase. This radial dependence also manifests itself in the anomalies of the temperature dependences of the hyperfine fields. The temperature anomaly is positive for Sn in Co₂MnGe and negative for Sn in Co₂MnSi.