Pressure dependence of the muon knight shift in antimony

The pressure dependence of the muon Knight shift in antimony has been measured at 30K using polycrystalline samples and at 10K using single crystals. A considerably stronger pressure dependence is observed with the field parallel to the c-axis than perpendicular. The deduced linear parts of the isotropic and axial pressure dependence are dK_iso/dP=−0.19(3)%/kbar and dK_ax/dP−0.24 (5)%/kbar. First principle molecular-cluster calculations show the origin, of the huge Knight shift and its pressure dependence.     

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.     

The giant muon Knight shift in antimony: Evidence for a Kondo impurity

A detailed study has been undertaken of the muon Knight shift in high purity antimony single crystals. No periodic variations with magnetic field (de Haas–van Alphen oscillations) are observed. The temperature dependence below 175 K is close to that expected for a Kondo‐like impurity with an anisotropic muon–electron hyperfine interaction. At higher temperatures the paramagnetic state becomes unstable and a transition occurs to a second state. The longitudinal relaxation rate rises from an apparently non‐zero value at T=0 to a maximum at 50 K, followed by a slow decline. This leads to a Korringa product which is strongly temperature dependent. This revised version was published online in August 2006 with corrections to the Cover Date.     

Field dependent specific heat and longitudinal magnetization of the quantum magnet layer Cs2CuCl4: Anisotropy effects

We have addressed the specific heat and magnetization of an anisotropic spin-1/2 triangular Heisenberg antiferromagnet Cs₂CuCl₄ in the presence of magnetic field at finite temperature. We have investigated the behavior of thermodynamic properties by means of excitation spectrum in terms of a hard core bosonic representation. The effect of in-plane anisotropy on thermodynamic properties has also been studied via the bosonic model by Green’s function approach. This anisotropy is considered for exchange constants that couple spin components perpendicular to magnetic field direction. We have found the temperature dependence of the specific heat and longitudinal magnetization in the gapped field induced spin-polarized phase for various magnetic fields and anisotropy parameters. Furthermore we have studied the magnetic field dependence of specific heat and magnetization for various anisotropy parameters. Our results show temperature dependence of specific heat includes a peak so that its temperature position goes to higher temperature with increase of magnetic field. We have found the magnetic field dependence of specific heat shows a monotonic decreasing behavior for various magnetic fields due to increase of energy gap in the excitation spectrum.     

高JcBi-2223银包套带材的电阻转变展宽与磁通钉扎

系统地研究了高J_cBi-2223相银包套带材在0—1T磁场下的电阻转变展宽.实验结果表明,Bi-2223带材的电阻转变具有热激活的性质.研究了磁通钉扎势与温度的关系,得到电阻转变曲线的温度关系为R(T)=R₀exp{-u₀(1-T/T_c)ⁿ/kT},其中磁场平行于ab面时,n=4.5;磁场垂直于ab面时,n=3.在磁场平行于ab面时,耗散与Lorentz力无关,只与平行于ab面的磁场大小有关,这可 关键词：     

Evaluation of asymmetric Mössbauer spectra of a Fe-41.3 at.% Ni invar alloy

Following a model of Billard and Chamberod the asymmetric Mössbauer spectra of a Fe-41.3 at.% Ni invar alloy have been quantitatively interpreted. In the temperature range from about 77 K up to the Curie temperature for each spectrum four parameter values have been obtained. These are the mean hyperfine field H₀, the magnetic field difference h₁ caused by the isotropic contribution of one first Fe-neighbour atom, the corresponding anisotropic difference h₂ and the strength of the anisotropic quadrupole interaction w. A physical interpretation of these parameters and their temperature dependence has been worked out. The last parameter shows an especially unexpected dependence which is strongly connected with the thermal expansion of the lattice. A mechanism seems to exist by which small changes of the lattice constant cause an enhanced variation of w.     

Possible observation of the coexistence of superconductivity and long-range magnetic order in NdRh4B4

The ternary rare earth compound NdRh₄B₄ has been studied by means of critical field, low temperature heat capacity, and static magnetic susceptibility measurements. Features in the upper critical field and heat capacity data at 1.31 K and 0.89 K suggest the occurrence of long-range magnetic order in the superconducting state. The temperature dependence of the static magnetic susceptibility follows a Curie-Weiss law with an effective magnetic moment μ_eff = 3.58 ± 0.05 μ_B and a Curie-Weiss temperature θ_p = ?6.2 ± 1.0 K between 20 K and room temperature. However,, magnetization vs. applied magnetic field isotherms suggest the development of a ferromagnetic component in the Nd³⁺ magnetization at low temperatures.     

Planar Hall effect in electrodeposited CoCu/Cu multilayer

Electrodeposited CoCu/Cu multilayers were investigated by measuring both anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) simultaneously. Studies have been carried out on a [Co(3 nm)/Cu(4 nm)]₅₀ multilayer sample, where a maximum of ?8.8 % GMR was observed at room temperature. A direct comparison of AMR and PHE output has been made both as a function of field and its relative orientation with respect to the current. Marked changes in PHE loops were observed at different angles (between magnetic field and applied current) whereas no noticeable changes could be found for AMR results. Such PHE outputs are the manifestations of complex spin reorganization due to strong antiferromagnetic-coupling between adjacent magnetic layers. In case of angular dependence output, when the applied field is less than the coercive field, the PHE output shows a deviation from the Sin2θ dependence that can be correlated to the domain wall propagation.     

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.     

Temperature dependence of the electric field gradient for111Cd in antimony

For the temperature dependence of the electric field gradient of¹¹¹Cd in the semimetal antimony the well knownT ^3/2 relationship is valid over a wide temperature range. The slope parameterB differs from that for^{121, 123}Sb in antimony by a factor of about 2.3.     

μ + Knight shift and spin relaxation in indium single crystalKnight shift and spin relaxation in indium single crystal

μ ⁺ SR measurements have been performed in a single crystal indium sample between 12 K and 300 K with a stroboscopic μSR spectrometer. The muonic Knight shiftK _μ and the muonic depolarization rate σ were obtained for various angles θ between the tetragonal crystallinec-axis and the direction of the external field. The isotropic part ofK _μ is only weakly temperature dependent and is consistent with the estimated Pauli spin susceptibility value. At a temperature of 12 K the angular dependence ofM ₂ (the second moment of the field distribution at the muon, obtained from the measured σ(θ) values) allows a clear determination of the muon location — the symmetric tetrahedral site. The observed anisotropicK _μ cannot be explained by the dipoles at the In atoms responsible for the bulk magnetic susceptibility but probably originates from an anisotropic Pauli spin susceptibility.     

XMCD study of the local magnetic and structural properties of microcrystalline NdFeB-based alloys

X-ray Magnetic Circular Dichroism (XMCD) technique was used to investigate local magnetic properties of microcrystalline Nd_10.4Zr_4.0Fe_79.2B_6.4 samples, oriented along either easy or hard magnetization direction. The Nd L _2,3 and Fe K edge XMCD spectra were measured at room temperature under a magnetic field of T. A very strong dependence of XMCD spectra on the sample orientation has been observed at the NdL _2,3-edges, whereas the Fe K-edge XMCD spectra are found to be practically isotropic. This result indicates that magnetic anisotropy of NdFeB-based alloys originates from the Nd sublattice. In addition, element selective magnetization curves have been recorded by measuring the intensity of XMCD signals as a function of an applied magnetic field up to T. To find a correlation between local and macroscopic magnetic properties of studied samples we compared these data with magnetization curves, measured by vibrating sample magnetometer up to T. Results are important for understanding the origin of high-coercivity state in NdFeB-based intermetallic compounds.     

Addition of nanometer SiC in the silver-sheathed Bi2223 superconducting tapes

Nanometer SiC particles were added to (Bi,Pb)₂Sr₂Ca₂Cu₃O_x (Bi2223) precursor powders and the powders were transformed into silver-sheathed superconducting tapes by the standard powder-in-tube (PIT) technique. The influence of SiC on the melting temperature, high-T_c (Bi2223) phase formation, microstructure and transport property of the tapes was studied by means of DTA, XRD, SEM/EDX, electrical and magnetic measurements. The results showed that SiC addition lowered the melting temperature of the superconductor powders and consequently, decreased the optimum sintering temperature of the tapes. However, the addition did not affect the Bi2223 phase formation and critical temperature (T_c) of the tapes up to 1.00 wt.% of SiC. Most importantly, the addition of a small amount of SiC (0.15 wt.%) improved the critical current (I_c) and I_c behavior in magnetic field as a result of the enhancement in density, grain alignment, grain connectivity and flux pinning of the tapes.     

Magnetosonic waves in antimony

A report is given on the observation of magnetosonic waves propagating through antimony in the Voigt-configuration. The waves were observed from a cut-off field and up to field of the order of 60 kG. The usual Alfvén-wave behavior as well as the influence of non-local effects were observed, the latter at the lower magnetic field values. The non-local effects are analysed in terms of the expressions given by Yokota and by Guthmann et al. It turns out, however, that these expressions are not able to account for the non-linear — in B^-1 — dispersion observed at the lower magnetic field values.     

Anomalous anisotropies and field dependencies of the muon Knight shift and the relaxation rate in monocrystalline Bi

The angular dependence of the muon Knight shift,K _μ, and the muon relaxation rate in Bi at 11 K were measured in external magnetic fields up to 1 T. BothK _μ and the second moment,M ₂, are field dependent and involveP ₄ ⁰(cos θ) andP ₄ ³(cos θ) terms in the angular dependence. The Knight shift behaviour is discussed in terms of the dipole-dipole interaction and the de Haas-van Alphen effect, a consistent interpretation was not achieved in either case. The field dependence ofM ₂ is in complete contrast to the second moment calculations and points to a field dependent redistribution of the charge distribution around the interstitial site.     

铁磁性的量子理论

本文用双时格林函数方法计算了铁磁性金属在整个温度范围内的自发磁化强度和磁各向异性常数K₁。计算中考虑了平均每个原子的d电子数非整数的事实和同一原子内d电子之间的交换作用。所得结果较普通Heisenberg模型的有所改进。K₁随温度的变化性质可以得到定性的解释。     

Magnetic and magnetocaloric properties of martensitic Ni2Mn1.4Sn0.6 Heusler alloy

The evolutions of magnetic properties at low temperatures and the influence of magnetic field on the temperature dependence of specific heat in martensitic Ni₂Mn_1.4Sn_0.6 Heusler alloy are studied. The frequency-dependent blocking temperature and considerable exchange bias below it are measured in the martensitic phase. From the analysis of the specific heat curves under magnetic field, a large inverse magnetocaloric effect manifested as the magnetic field induced rise of isothermal magnetic entropy and/or magnetic field induced adiabatic temperature decrease in the vicinity of the reverse magnetostructural transformation and a significant value of the conventional magnetocaloric effect at the Curie temperature are obtained. The Debye temperature and electronic coefficient equal to Θ_D=310±2 K and γ= 16.6±0.3 mJ/K²mol, respectively, do not depend on the magnetic field.     

Magnetoresonance EMF in thin manganite films

The effect of magnetoresonance emf (MREMF) in thin epitaxial films of rare-earth manganites La_0.67Sr_0.33MnO₃ is detected and investigated. The effect is manifested in the occurrence of a constant voltage under the action of microwave pumping in magnetic fields corresponding to ferromagnetic resonance conditions. The MREMF signal includes symmetric and antisymmetric components and changes its polarity upon switching of the external magnetic field. The temperature dependence of the effect (including the range in the neighborhood of the phase transition) is analyzed. The experimental data including the shape of the signal and its dependence of the field orientation are in good agreement with the results obtained in the theoretical model based on the mechanism of anisotropic magnetoresistance. It is shown that the magnetoresistance anisotropy in the manganite under investigation is negative and sharply attenuates as the temperature approaches the Curie point, almost vanishing in the paramagnetic phase.     

Temperature dependence study of the quadrupole interaction of111Cd in antimony

A power law dependence has been observed for the temperature dependence of the quadrupole interaction of the 247 keV state of¹¹¹Cd in antimony, which is similar to that observed for¹²¹Sb and¹²³Sb in antimony.Supported in part by the US Energy Research and Development Administration.