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We have studied the electronic specific heat of various nickel-platinum alloys near the critical concentration for the appearance of ferromagnetism. The electronic specific heat coefficient has a maximum for an atomic concentration of 42.5 ± 0.5% nickel. This maximum coincides with that of the high field susceptibility. The results obtained are discussed qualitatively.

We report magnetization, resistivity and small angle neutron scattering experiments on cubic B20 FexCo1−x SI alloys (0.3 ⩽ x ⩽ 0.9) and CoxMn1−xSi allpys (x = 0.02, 0.04 and 0.06). The magnetically ordered FexCo1−xSi alloys and the CoxMn1−xSi alloys with x = 0.02 and 0.04 are found to be helimagnetic with very long period. The low temperature resistivity of the magnetically ordered FexCo1−xSi alloys exhibits an anomalous positive magnetic contribution. The occurence of the Dzyalosyinsky-Moriya spin-orbit type interaction in these non-centrosymmetric alloys is given as a possible explanation of the helimagnetic order.

The authors have studied the high field susceptibility of nickel-platinum alloys in fields up to 150 kOe, at temperatures between 4.2 and 300K. The high field susceptibility is analysed in the ferromagnetic and paramagnetic range by means of Arrott plots and Landau coefficients. The paramagnetic initial susceptibility follows a Curie-Weiss law, with a Curie constant independent of nickel concentration. The results are compared with those obtained for palladium-nickel alloys. The experimental data are discussed in the framework of recent theories on itinerant ferromagnetism.

We measure the thermal expansion, electrical resistivity, and magnetic susceptibility of PbMo6S8 single crystals (with aTc value of 14.2 K) along a twofold and a threefold axis. We find a large anisotropy in the three types of measurements. Results are discussed in terms of peculiarities of the phonon spectrum of Chevrel-phase compounds.

Magnetization, resistivity, thermal expansion coefficient, and x-ray unit-cell measurements of ${\mathrm{Yb}}_{0.4}$${\mathrm{In}}_{0.6}$${\mathrm{Cu}}_{2}$ under pressure (P up to 25 kbar) and in magnetic fields (${H}_{\mathrm{ext}}$ up to 180 kOe) at temperatures 4.2--80 K have been performed. The valence-phase-transition temperature, ${T}_{v}$, is pressure dependent and surprisingly enough also field dependent. One obtains ${\mathrm{dT}}_{v}$/dP=-2.1 K/kbar for P6 kbar. Negative chemical pressure obtained by substituting Yb by La or Cu by Ag increases ${T}_{v}$. A theoretical analysis within a previously published model shows that the interconfigurational excitation energy below ${T}_{v}$ changes with pressure at a rate ${\mathrm{dE}}_{0}$/dP=-11 K/kbar. The external magnetic field does not affect ${E}_{0}$, but it increases the ${\mathrm{Yb}}^{3+}$ excited-state population and thus drives the phase transition to a lower temperature at a rate ${\mathrm{dT}}_{v}$/${\mathrm{dH}}_{\mathrm{ext}=\mathrm{\ensuremath{-}}}$0.022 K/kOe.

High T c superconductors and heavy fermions have some similar properties. Intermediate valency state exists or can be induced by impurities or by off-stoichiometry composition. All these compounds have a Fermi liquid behaviour below a characteristic temperature T SF corresponding to the band width of quasiparticles. Strong spin correlations could also exist in the high T c superconductors. Evidence is given that all these materials have one energy scale T SF as observed in 3 He which is known as being a strongly correlated Fermi liquid. All the critical temperatures T c are nearly proportional to this energy scale T c ∼ 1 γ∼ T SF , γ being the electronic specific heat coefficient per unit of volume. The superconductivity could have the same origin in the high T c oxides and in the heavy fermions systems.

We discuss the weak ferromagnetic properties of the two series of alloys Fe x Co 1− x Ti and Fe x Co 1− x Si in the light of new specific heat and resistivity studies as well as high field and high pressure magnetic measurements.

The superconducting and magnetic properties of the Yb /SUB 1.2-x/ Eu /SUB x/ Mo/sub 6/S/sub 8/ series of compounds have been investigated by means of ac magnetic susceptibility, electrical resistivity, and upper critical magnetic field H /SUB c2/ measurements. The superconducting transition temperature at ambient pressure is depressed by Eu additions, until superconductivity disappears completely at x about0.7. For Eu concentrations x

The 4.2K magnetization of several Pd-Ni alloys, with concentration up to 5% Ni was measured in magnetic fields up to 50 kOe and at pressures up to 7 kbar. The results are interpreted using a local model for the appearance of ferromagnetism by the creation of giant induced moments on the non magnetic sites.

Magnetization, NMR and coercive force measurements were performed on amorphous Ni1−cPc alloys for concentration ranging between 0.15 and 0.25. The experimental results show that the magnetism is not of the same nature below and above some critical concentration c0 which determines the concentration ranges: the first one (0.15 < c < 0.18) presents the characters of a weak homogeneous ferromagnetism, while inhomogeneities dominate the magnetic properties of the second one (0.18 < c < 0.25).

The magnetic properties such as Curie temperatures, spontaneous magnetizations, paramagnetic susceptibilities and their pressure derivatives of PdNi alloys with nickel concentrations below 15% have been measured. All these properties (from our measurements as well from previously published measured values for nickel concentrations up to 40%) are well described in a local model of coupling between nickel moments through the palladium matrix. From the concentration dependence of the Curie temperature and its pressure variation the authors derived values for the exchange integral between localized moments and d electrons and for its pressure derivative in agreement with values found in the case of PdFe and PdCo alloys. The paramagnetic susceptibilities follow a Curie-Weiss law. There exist concentration ranges where the spontaneous magnetization as well as its pressure derivative vary proportionally to the concentration.

We have measured the thermal variation of the magnetization of weakly ferromagnetic Ni0.47Pt0.53, Ni0.52Pt0.48, Ni0.04Pd0.96 and Ni0.05Pd0.95 alloys in fields up to 150 kOe. The values of the stiffness coefficients D for the magnon dispersion curves are deduced. Small angle neutron scattering measurements with and without a magnetic field were carried out on Ni0.45Pt0.55, Ni0.50Pt0.50 and Ni0.04Pd0.96 alloys. An independent measurement of D has been obtained from the cut off angle of the intensity of the scattered neutrons. The results are compared.

The authors have measured the magnetisation of ferromagnetic pseudobinary FexCo1-xTi alloys in fields up to 150 kOe, at temperatures between 1.4 and 300K and under high pressures up to 7 kbar. They have analysed the temperature dependence of the spontaneous magnetisation. Their experimental results suggest that the alloys, weak itinerant ferromagnets for x 0.5. The results are analysed in terms of indirect coupling models.

The properties of Yb 1.2−x Eu x Mo 6 S 8 compounds have been investigated by means of electrical resistivity and ac magnetic susceptibility measurements under hydrostatic pressure up to 20 kbar and quasi-hydrostatic pressure up to 100 kbar. A temperature-pressure-Eu concentration phase diagram showing the crystallographic, normal and superconducting phases of these compounds was constructed Les proprietes des composes pseudoternaires Yb 1.2−x Eu x Mo 6 S 8 ont ete etudiees a l'aide des mesures de resistivite electrique et de susceptibilite magnetique ac sous pression hydrostatique jusqu'a 20 kbar et quasi hydrostatique jusqu'a 100 kbar. Un diagramme de phase de temperature-pression-concentration d'Eu montrant les phases cristallographiques, normales et superconductrices de ces composes a ete construit

Accurate high pressure X-ray diffraction experiments performed on a powdered single crystal of CeAl2 do not show any sizeable volume anomaly up to 150 kbar. However, high pressure electrical resistance experiments performed on a single crystal of the same batch show a continuous anomaly near 80 kbar at room temperature, i.e. close to the pressure for which Croft and Jayaraman [2] observed a strong volume anomaly. The resistance anomaly has been followed down to 2 K leading to a new line in the P-T diagram of CeAl2. This line, interpreted in terms of a crossover between two different Kondo regimes, crosses the critical line where magnetic order takes place. On the basis of our results in CeAl2, a detailed phase diagram for magnetically ordered Kondo compounds is proposed and discussed.

We have investigated under high pressure a sintered L~~CU~.~~O~-, sample which exhibits bulk supercon- ductivity below Tc 2( 37 K and antiferromagnetic ordering below TN N 240 K. dTN ldp has been determined using d.c. susceptibility and resistivity measurements under pressure. dTc ldp and dTN ldp are found to have opposit signs. This experimental result is confronted to the theory.

The resistivity of the heavy fermion compound CeInCu2 has been measured under pressure up to 1.55 GPa (15.5 kbar); the resistivity maximum is swept from 23 K to 80 K with increasing pressure. The compressibility was measured at room temperature, as well as the thermal expansion between 1.2 and 50 K. The Gruneisen parameter evaluated from the shift of the resistivity curve is about 26, the value deduced from the thermal expansion, specific heat and compressibility being 42.

We have determined the effect of uniaxial stress on the magnetic transition temperatures of gadolinium, terbium, and dysprosium. The problem of stress homogeneity has received particular attention. From the variation with stress of the Curie (Gd) or Neel (Tb, Dy) temperatures, spontaneous magnetostriction in Gd, Tb, and Dy is quantitatively interpreted.

The (FeTi)x(CoTi)1−x pseudobinary alloys are weekly ferromagnetic in the range 0.4

The effects of both high magnetic field and high pressure on the magnetic and superconducting properties of the compound Y9Co7 have been studied via magnetization and low field ac susceptibility measurements. The results imply that the magnetic state at ambient pressure is that of nearly ferromagnetic Fermi systems and most likely is quasi‐low‐dimensional in character. We find that the dependence of the magnetization on the field has the unusual form M(H)=M* exp−(H*/H),1/4 where M* and H* are temperature dependent parameters. Application of pressure rapidly suppresses the magnetic interactions whereas it enhances the superconducting transition temperature. This suggests coexistence of magnetism and superconductivity.

High pressure electrical resistance experiments performed on a single crystal of CeAl2 allow one to determine a characteristic line in the pressure-temperature plane where a continuous passage from weak to strong Kondo behaviour is observed. This line is not associated with any sizeable volume anomaly as shown by X-ray experiments.

The electrical resistivity of CePd3 has been measured between 1.5 and 300 K under hydrostatic pressures up to 20 kbar. The temperature TM for the maximum of resistivity increases with pressure at the rate dTMdp = 0.65 K kbar−1. The value, −5.2, found for ∂ lnM∂ lnV is in good agreement with previous data based on elasticity measurements and thermodynamical properties.

At 300 and 4 K, the CeSn 3 anomalous compressibility indicates a pressure induced valence change. The thermal contraction from 300 to 4 K is equivalent to that produced by a pressure of 8 kbar. High pressure susceptibility data show that the thermal expansion does not drive the “magnetic-nonmagnetic” transition of CeSn 3 .

Recent results are reported on the Kondo lattice compound CePt2Si2. Specific heat data present two anomalies in the range 20–100 K, associated with crystal field and incoherent Kondo effect. A maximum in C/T is observed around 1.4 K, which could be attributed to coherence effects. Resistivity and susceptibility measurements under pressure are also presented.

An experimental study on amorphous electrodeposited Ni 1− c P c alloys was performed using measurements of magnetic properties, coercive force, NMR and resistivity at low temperatures. The results show that weak ferromagnetism takes place for 0.15 c

We report here results from a study of superconductivity in the Sm 1.85 (Ce 0.15−x Th x )CuO 4−y system. We observe resistive superconducting transitions for all values of x, with transition midpoints ranging from 19.3 K for x =0 to 1.9 K for x =0.15. This is the first reported observation of superconductivity in the compound Sm 1.85 Th 0.15 CuO 4−y . Magnetic susceptibility measurements performed on this compound verify the presence of superconductivity. Additionally, electrical resistivity measurements done under pressure show a decrease in T c in Sm 1.85 Th 0.15 CuO 4−y at a rate dT c /dP=-0.043 K/kbar.

The electrical resistivity of CeMg has been measured under pressures up to 105 kbar. The Neel temperature continuously decreases, while the amplitude of the magnetic term as well as the negative slope at high temperature increase. We deduce the variation of the coupling constant Γ as a function of pressure.

We have measured the ordered moment μ s of UN under pressure up to 30 kbar. It is found to decrease rapidly at exactly the same rate as T N = d log μ s /d log V = d log T N /d V = 19. This is taken as good experimental evidence that UN is a band antiferromagnet.

Magnetization measurements of amorphous FeGe alloys containing 20 and 30 at.% iron have been made under high field and high pressure. These alloys possess a weakly itinerant ferromagnetic character although large inhomogeneous effects are superposed.

The cubic Laves phase of YCo2 has a strongly enhanced susceptibility χy. The variation of χy with pressure at 40 K has been measured and the initial slope is d log χy/d log V = 14 ± 2. This result is correlated with the pressure dependence of the Curie temperatures of A Co2 alloys.

Novel high-T c superconductors La2−x Bi x′ Sr x−x′ CuO4−y have been isolated and studied. The influence of the experimental conditions of synthesis on the superconductivity has been especially studied for the composition La1.7Bi0.1Sr0.2CuO4−y ; it is shown thatT c decreases as oxygen is introduced into the matrix, likely due to the partial oxidation of Bi(III) to Bi(V). The highT c value observed for one sample (T c ≃42 K), as compared withT c ≃38 K of La1.8Sr0.2CuO4−y suggests that bismuth is also a potential candidate for improving the superconducting properties in these oxides.

Disordered FexCo1−xSi alloys are known to be ferromagnetic in an iron concentration range starting at x = 0.2. We have measured their magnetization in magnetic fields up to 40 kOe at 4.2 K and under hydrostatic pressures up to 8 kbar, as well as their zero pressure susceptibility at 4.2 K in high magnetic fields of 150 kOe. We have also determined the Curie temperatures of the ferromagnetic samples under hydrostatic pressure up to 8 kbar from the temperature variation of the initial susceptibility. We determined a critical iron concentration of x ≃ 0.95 for ferromagnetism in FeSi rich alloys. From some of our results, the ferromagnetism in the CoSi rich alloys seems to appear in a rather homogeneous way, whereas the FeSi rich alloys in contrast exhibit local effects.

In this work we study a sintered La2CuxO4−y sample corresponding to the initial stoichiometry x=1.02 which is anti ferromagnetic with a Neel temperature TN=240 K and superconductor below Tc=37 K. Antiferromagnetism coexists with superconductivity in the bulk as deduced from susceptibility and magnetization measurements. Antiferromagnetic order is characterized by an anomaly of resistivity, a maximum in DC susceptibility and a metamagnetic transition. TN decreases under hydrostatic pressure (H.P.). Under quasihydrostatic pressrure (Q.H.P.), the superconducting transition becomes incomplete and the antiferromagnetic ordering is suppressed. The superconducting transition temperature (Tc(p)) passes through a maximum for P⋍40 kbar. Under Q.H.P. the sample exhibits a resistivity behaviour, p ∝ exp (T0Tα with 0.25

Bulk superconductivity is present in La 2 Cu x O 4 − y for 0.98 ⩽ x ⩽ 1.04 and for an y value which is strongly reduced by annealing under high pressure of oxygen. Two superconducting temperatures are observed T 2 and T c ; the first one, T 2 = 37 K, corresponds to the resistivity fall; the second one, T c , corresponds to the appearance of diamagnetism. T 2 and the critical fields of samples stay unchanged whatever the normal state resistivity is, even if it varies by a factor 40000 from a semi conducting to a metallic state. Then a conventional mechanism of pairing is unconceivable. The existence of a bump in the resistivity at T = 220 K of samples which undergo a superconducting transition suggest a possible correlation between coherence effects among copper spins and superconductivity.

The magnetic moments of transition atoms in disordered‐concentrated metallic alloys depend on their immediate surrounding as well as on the mean electronic properties of the alloys. We discuss, using a few examples, the homogeneity of these alloys in the concentration range for the onset of ferromagnetism and of the effects of high magnetic fields, temperatures and pressures on their magnetic moment. Among the examples chosen are the NixOt1−x, NixPd1−x, FexGe1−x, FexCo1−xSi and rare earth‐yttrium‐cobalt Y1−xTxCo2 systems. Their physical properties are largely dependent on non‐strongly magnetic transition atoms.

Nous avons mesure la variation avec les contraintes uniaxiales de la temperature de Neel du terbium et de la temperature de transition ferromagnetique-helimagnetique du dysprosium. Dans une etude preliminaire nous avons determine par photoelasticite la repartition des contraintes a l'interieur d'echantillons en resine photoelastique de forme cubique ou spherique.

The electrical resistivity of Li 0.9 Mo 6 O 17 single crystal has been studied between 1.5 K and 300 K under hydrostatic pressures up to 20 kbar. A large increase of the superconducting transition temperature, from 1.7 K to 2.5 K, is associated to a sharp decrease of the temperature T m of the electronic, probably CDW instability.

Powdered Ba 0.6 K 0.4 BiO 3−y was synthesized using a two steps technique. The samples are cubic with a= 4.281(1). The transition temperature (Tc) is determined from a c susceptibility (Tcζ) as well as from resistivity measurements on pellets (Tc ϱ ). Tc is found to be dependent (25.5–27 K) related to the annealing temperature. Besides, Tc ζ > Tc ϱ is unusual and anomalous magnetoresistive effects are measured between Tc ϱ and Tc ζ . Both effects are discussed in terms of weakly coupled superconducting grains.

The magnetic properties of disordered Pd-Ni alloys, with low nickel content have been studied at high magnetic fields and high pressures. The variation of the saturation magnetization and Curie temperature with the concentration and pressure are described.