Formation andstability of magnetic moment on isolated Rh impurities in dilute PtFe alloys

The local susceptibilities (T) of isolated Rh impurities in paramagnetic dilute Pt(Fe) alloys have been measured using the TDPAC method. The results show existence of 4d magnetic moment for Rh with reduced spin fluctuation temperatures (T _sf). It is suggested that moment stability scaled byT _sf is governed mainly by the interatomic d-d exchange interaction caused by induced ferromagnetic polarization of host d band electrons.     

Superconductivity and resistance behaviour of σ-phase alloys: Nb−Rh and Ta−Rh

Superconductivity, structure and electrical resistance behaviour of -phase alloys of Nb–Rh and Ta–Rh are investigated. The Ta–Rh alloys do not become superconducting above 1.2 K. The andH _c2 (0) values of a homogeneous alloy with the composition Nb_65.2Rh_34.8 are 2.95 K, 13.9 kG/K and 23 kG, respectively, whereas for an inhomogeneous alloy with the composition Nb_63.7Rh_36.3 these values are 4.24 K, 5.5 kG/K and 14 kG, respectively. Splat quenching results in a substantial increase in the andH _c2 (0) values of the Rh-rich sample. Annealing (900°C, 100 h) of the Rh-rich sample leads only to small changes in the superconducting properties but a small amount of Nb–Rh solid solution has been formed. The electrical resistance of Nb_65.2Rh_34.8 decreases with decreasing temperature and varies asT ^0.5 between 150 and 240 K and asT between 60 and 140 K. For Ta_70.0Rh_30.0 the temperature coefficient changes to negative values below 170K. values are calculated for Nb–Rh using McMillan's formula. An estimatedT _c value of Ta–Rh is 0.2 K. TheH _c2 (0) values of Nb–Rh are in good agreement with the theoreticalH _c ^2** (0) values.Dedicated to Prof. Dr. W. Buckel on the occasion of his 60th birthday     

Polarized fluorescence and absorption spectroscopy of 1,32-dihydroxy-dotriacontane-bis-rhodamine 101 ester. A new and lipid bilayer-spanning probe

We report on the properties of 1,32-dihydroxy-dotriacontane-bis-rhodamine 101 ester (Rh101C₃₂Rh101) in lipid bilayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and in liquid solvents. The results are compared with those of rhodamine 101 octadecanyl ester (Rh101C₁₈). Both molecules are solubilized in the lipid bilayer and the Rh101 moieties are anchored in the lipid-water interface, so that the electronic transition dipole moments (S ₀ S ₁) are oriented preferentially in the plane of the bilayer. At low concentrations of the dyes in lipid bilayers of DOPC, the fluorescence relaxation is single exponential with a lifetime of =4.9±0.2 ns. The relative fluorescence quantum yield of _C32/_C18 0.95 in DOPC vesicles. These results strongly suggest that only a small fraction of the Rh101C₃₂Rh101 molecules are quenched, by, for example, intra- or intermolecular dimers in the ground state at mole fractions of less than 0.1% in the lipid bilayers. For Rh101C₃₂Rh101 in lipid vesicles, the steady-state and time-resolved fluorescence anisotropies are compatible with efficient intramolecular electronic energy transfer. It is concluded that nearly every Rh101C₃₂Rh101 molecule is spanning across the lipid bilayer of DOPC.     

Über die Supraleitung von Hf-Rh-Legierungen

The transition temperaturesT _c of quenched Hf- Rh alloys are strongly increased in the hexagonal phase by Rh, similar to the homologous systems Ti-Rh and Zr-Rh. On the other hand a stabilization of the cubic high-temperature phase by Rh has not been possible. At higher amounts of Rh(>6 at%) the intermetallic compound Hf₂Rh with aT _c of 1.98 °K is formed. Moreover a transition temperature of 1.73 °K is found which is probably due to the intermetallic compound HfRh. The results above are interpreted with the help of X-ray diffraction and metallurgic techniques.     

Rotational bands and signature inversion phenomena in πh9/2⊗νi13/2 and πi13/2⊗νi13/2 structures in odd-odd 176Ir

The ^109,111,113Rh nuclei have been produced as fission fragments in the fusion reaction ¹⁸O + ²⁰⁸Pb at 85 MeV. Their level schemes have been built from gamma-rays detected using the Euroball IV array. High-spin states of the neutron-rich ^111,113Rh nuclei have been identified for the first time. Several rotational bands with the odd proton occupying the πg _9/2, πp _1/2 and π(g _7/2/d _5/2) sub-shells have been observed. A band of low-energy transitions has been identified at excitation energy around 2 MeV in ^109,111Rh, which can be interpreted in terms of three-quasiparticle excitation, πg _9/2νh _11/2νg _7/2/d _5/2. In addition another structure built on states located at low excitation energy (608 keV in ¹¹¹Rh, 570 keV in ¹¹³Rh) points out that, as already observed in the lighter isotopes ^107,109Rh, triaxial deformation plays a role in the neutron-rich Rh isotopes well beyond the mid-shell. Received: 15 July 2002 / Accepted: 9 October 2002 / Published online: 3 December 2002 RID="a" ID="a"e-mail: porquet@csnsm.in2p3.fr RID="b" ID="b"Present address: CSNSM IN2P3-CNRS and Université Paris-Sud 91405 Orsay, France. RID="c" ID="c"Present address: CEA/Saclay, DSM/DAPNIA/SPhN, 91191 Gif-sur-Yvette Cedex, France. Communicated by D. Schwalm     

Au-197 Mössbauer isomer shift in Au-Cu and Au-Ag alloys: The role of the Au 5d electrons

The Au-197 Mössbauer isomer shift (IS) for a series of Au-Cu and Au-Ag alloys is correlated with the change in the 5d electron population (5d hole count) at the Au site upon alloying. The Au 5d hole counts have been derived from the area under the whiteline of the Au L_3,2 edge X-ray absorption near edge structures (XANES) of the alloys. It is found that there exists a linear corelation betweenIS and Au 5d hole counts, indicating that the redistribution of 5d electrons has a significant effect on the isomer shift. From theIS-5d hole correlation, the ratio of 5d loss to 6s gain ( n _d / n _s ) is determined to be –0.62.     

Surface-induced disordering at first-order transitions in body-centered cubic binary alloys: A Monte-Carlo simulation

Surface effects on the phase transition from theDO ₃ phase to the disordered phase are studied for a bcc Ising antiferromagnet with nearest and next-nearest neighbor exchange interactions in a magnetic field. This model can also be considered to represent binary alloys such as the FeAl-system; missing interactions near the surface translate then into surface magnetic fields. The change of the local magnetization near the surface then corresponds to surface enrichment of one component. For a plausible choice of parameters surface-induced disordering is found and the associated critical behavior is studied. Varying the bulk fieldH near the transition fieldH _c , we find that the thickness of the disordered layer increases proportional to ln(H-H _c ) while the local order parameter at the surface vanishes as (H-H _c )^1/2. These results are consistent with mean field predictions for the single order parameter case, although several ordering fields occur (sublattice magnetizations and magnetization).     

Specific heat of Nickel-Iron and Nickel-Cobalt alloys between 600° K and 1500° K

The -specific heat anomalies of ferromagnetic fcc Ni–Co and Ni–Fe alloys were investigated near the Curie temperatures. The magnetic contribution to the specific heat was found to be logarithmically divergent [c _M=log|T/T _c–1| ^A ] above the Curie temperature. The exponentA was composition dependent. Entropy and energy values associated with magnetic transions were determined experimentally and compared with theoretical predictions of the Heisenberg and Ising localized electron models obtained from series expansion calculations.     

Untersuchungen zur Supraleitung des Legierungssystems Zr-Rh

The transition temperatures of Zr-Rh alloys with small amounts of Rh are essentially higher than the transition temperature of pure Zr. Rhodium is not dissolved in the Zr lattice. In the unannealed specimens Rh stabilizes the body centered cubic phase which has aT _c of 6.4°K. After annealing an intermetallic compound is formed with aT _c of about 12°K. This compound is also formed in the unannealed specimens at higher Rh content.     

Low temperature specific heats of very dilute alloys of Ce in Al

Measurements of the specific heat of two alloys of Ce (0.00275 and 0.0121 at % Ce) in Al have been made in the region 0.3<T<3.8 K. Within the limits of detection (<1 ppm), the alloys contained no metallic impurities other than Ce and their homogeneity was checked by neutron activation analysis. For the alloys in their normal electronic states, the change/c was found to be 6±3 and 3.5±1.5mJ/at% K². The behavior of the alloys in their superconducting states (e.g.: the shift ofT _c with the concentration of Ce; the correlation betweenT _C/T_C0 andC/C ₀) indicates the existence of short-lived local moments associated with the Ce impurities.     

Hyperfine-field measurements inCr Rh andCr Re alloys using perturbed angular correlation technique

The hyperfine fields on¹¹¹Cd probe nuclei in Cr (1 at% Rh), Cr (0.3 at% Rh) and Cr (0.5 at% Re) matrices are measured using time-differential perturbed (–) angular correlation of 173–247 keV cascade in the decay of¹¹¹In to the levels in¹¹¹Cd. The sources prepared by ion implantation of¹¹¹In (2.81 d) activity followed by appropriate annealing procedure were found to be of good quality. The addition of impurities, located to the right of chromium in the periodic table such as Rh and Re, to the chromium matrix increases the electron to atom ratio, resulting in an increase in the magnetic moment compared to pure chromium. This in turn is expected to result in an increase in the hyperfine fields at probe nuclei in these alloys. The measured hyperfine fields are in qualitative agreement with the expected changes in these alloys.On leave from Kanpur Institute of Technology.     

Effect of hydrogen on the hyperfine magnetic field in crystalline Zr-Fe alloys

This paper deals with room temperature⁵⁷Fe Mössbauer studies performed on crystalline Zr_1–y Fe _y and Zr_1–y Fe _y H _x (0.05y0.5) alloys. For hydrogenated alloys, the transition from parato ferromagnetic behaviour is observed aty = 0.25, i.e. a considerably lower concentration of iron compared to uncharged alloys. It seems to be not only attributable to ZrFe₂ formation. Apart from ZrFe₂, a relatively intensive and quite different than the ZrFe₂ contribution to theP(B) distribution has been observed for hydrogen charged alloys with only 25 at.% Fe. It is linked to the origin of the additional magnetic component due to hydrogen absorption in which Fe has less than 6 Fe nearest neighbours.     

Magnetic properties of amorphous MnxPd82−xGe18 alloys

Magnetoresistivity, magnetic, susceptibility and high field magnetization measurements were performed on the amorphous Mn _x Pd_82–x Ge₁₈ alloys for 1x7. These amorphous alloys were prepared by radio frequency (R. F.) sputtering using argon, depositing onto fused quartz substrates to a thickness of about 20 microns. The negative magnetoresistivity is approximately proportional to the square of the magnetization and the susceptibility obeying the Curie-Weiss law between 18 and 293 K. These results lead to the conclusion that a Kondo-type s-d exchange interaction exists in the amorphous Mn-Pd-Ge alloys and the d-d, spin correlation between magnetic atoms is, in general, weaker in the amorphous alloys than in the corresponding crystalline alloys.     

Lattice dynamics of a Pd0.90Rh0.10 crystal

Using inelastic neutron scattering, the phonon dispersion relations along the [100], [110] and [111] directions of a single crystal of Pd_0.90Rh_0.10 have been measured at 296K. From these results and phonon data for Pd, the phonon frequency shifts,(q), and the self-energy function, _j (q, _j (q)), have been determined for all branches. The frequency changes exhibit large wave vector and polarization dependence and behave non linearly with the increase concentration of Rh. The seventh neighbour tensor Born-von Kármán model has been fitted to the experimental phonon dispersion curves, and the force constants and elastic constants calculated. Correlations between the phonon anomalies, displayed in the slope ofT ₁ [110] branch, and the structure of the generalized susceptibility function, ₀(q), for Pd were discussed. From which follows the influence of the electron-electron interaction on theT ₁ [110] branch in Pd and Pd-Rh alloys.     

Mössbauer study of Fe-Al disordered alloys near the critical concentration

Disordered bcc Fe_1–q Al _q alloys in the composition range 0.5q0.6 were studied by Mössbauer effect measurements. The Mössbauer spectra at 300 K of all the samples consist of two paramagnetic sites, one is a singlet and the other a doublet with quadrupole splitting. The results can be interpreted by considering that the sites of this disordered system are arranged near the configurations of the Fe and Al sites of the Fe-Al ordered system.     

Scale Factor,Intensity of Measuring Phase State,and Peculiar Features of Atomic Volume Behavior during Martensitic Transformations in Low-Stability Alloys Based on Titanium Nickelide

The paper presents an analysis of regular features of variations in phase composition and atomic volume of the austenite and martensite phases, and the value of Bein's deformation during thermoelastic martensitic transformations versus crystallochemical factors in low-stability alloys based on titanium nickelide doped by different elements (Fe, Co, Rh, Cu, Pd, Pt, Au). It is established that the low-stability alloys undergoing different sequences of martensitic transformations (B2–B19, B2–B19, B2–R–B19) demonstrate different values and character of the atomic hopping range during transformation.     

Bain strain upon thermoelastic martensitic transformation in intermetallic compounds based on titanium nickelide

Analysis of our original results and the data in the literature on the behavior of structural parameters of the austenitic and martensitic phases near phase transitions in alloys of the TiNi-TiMe (Me = Au, Pd, Pt, Rh, Cu, Co, Fe, Rh) system has been performed. It is established that the Bain strain and dilatation changes depend on the martensitic transformation “channel.”     

Deformation hardening and the temperature dependence of the mechanical properties of ternary ordering alloys. Part II

Yield point, hardening factor, and elastic modulus are reported as functions of quenching and test temperatures for the alloys Ni₃(Fe + 3 at% Al), Ni₃(Fe + 3 at% Mn). A maximum is found in the mechanical properties near the critical temperature T_cr; this does not occur for alloys in the disordered state. The deformation aging under load is examined near this maximum and at 200 ° C. A range of linear hardening occurs up to e of 15–18% in ordered alloys, which is replaced by a range of decreasing hardening coefficient at higher . The results are discussed by reference to earlier ones for Ni₃Fe, Ni₃(FeCr). Ni₃(FeMo).     

Heavy-fermion behavior and spin-glass freezing in Si-stabilized amorphous alloys based on UPt3

U-Pt-Si and U-(Pt, Pd)-Si alloys have been prepared in the amorphous state by splat-cooling. The average nearest-neighbor distance is the same as the U-Pt distance in UPt₃. The low-temperature behavior of these alloys (with composition (U_0.25Pt_0.75)_1–xSi_x, x=0.18, 0.20, 0.25; and (U_0.25(Pt_1–yPd_y)_{0.75 0.8}Si_0.2,y=0.05 and 0.1) has been studied by specific heatC, magnetization and resistivity measurements in the temperature range 1.5 K to 20 K and for magnetic fields up to 6 T. Some samples were investigated down to 0.1 K and the specific heat for one sample was measured in fields up to 22 T. With ₀ =C/T| _T0 between 0.25 and 0.35 J/moleUK², the alloys can be classified as heavy-fermion materials. As opposed to UPt₃, the alloys exhibit spin-glass behavior with a concomitant decrease of ₀. The magnetization exhibits typical spin-glass features (e.g., an irreversibility line). An inverse relationship between ₀ andT _max (temperature ofC/T maximum which is proportional to the spin-glass freezing temperature), irrespective of the Pd content, is observed. The behavior can be qualitatively described by a coexistence of heavy-fermion behavior and spin-glass freezing.     

μSR study of UTr2Si2, Tr=Co,Rh OR Pt

We have studied bySR spectroscopy the intermetallicsUTr ₂Si₂ where Tr=Co, Rh or Pt. Whereas for the Co compound we only get information on the muon localisation site, from the other two materials we obtain information on their electronic properties. We compare the characteristics of theirSR response.