Search

In this work we present a magnetoresistance study on the CeRu2Ge2 compound. We analyze the ρ(T) curves for several applied magnetic fields using the electron–magnon scattering model for a ferromagnetic spin arrangement. From this analysis, the field dependence of the energy gap of the magnon spectrum is obtained. The magnetoresistance ρ(H) at various temperatures arises from a normal metal contribution with an additional scattering mechanism due to electron–magnon interaction.

We report pressure and temperature dependent electrical resistivity measurements in the Ce 2 Rh 1 - x Ir x In 8 alloys. Our results revealed two phases with zero resistance. One of these phases is induced by pressure, occurring for a range of compositions situated near the Rh-rich extreme, consistent with the behavior observed for the pure Ce 2 RhIn 8 compound. The second transition occurs for intermediate concentrations ( x ∼ 0.5 – 0.7 ) , and in sharp contrast with the first transition, is progressively eliminated by the application of pressure. We compare the findings in the Ce 2 Rh 1 - x Ir x In 8 alloys to its related CeRh 1 - x Ir x In 5 , discussing how the occurrence of the superconducting phases may become unfavorable for the bi-layer alloys due to higher dimensionality and stronger disorder.

In this work a preliminary pressure–temperature–composition phase diagram for the Ce 2 Rh ( 1 - x ) Ir x In 8 heavy-fermions (HF) materials is reported, built from pressure-dependent electrical resistivity ( ρ ( T ) ) measurements on single-crystalline samples. Although neither of the two end members is an ambient-pressure SC, a transition to a zero-resistance (ZR) state was found at ambient pressure ( T C ≈ 600 mK ) in a narrow Ir concentration range (around x = 0.5 ). Pressures not higher than 10 kbar are sufficient to suppress this ZR state for all measured concentrations, in contrast to the 115 materials.

Experiments of electrical resistivity as a function of hydrostatic pressure for single crystals of Sn-doped CeCoIn 5 are reported. Due to the subtle Sn-doping, T c is strongly suppressed from T c = 2.3 K of undoped CeCoIn 5 to T c ∼ 0.7 K for the reported concentration ( x ∼ 0.12 ). As for pure CeCoIn 5 , superconductivity (SC) seems to evolve out of a non-Fermi liquid (NFL) normal state just above T c . A temperature–pressure phase diagram is constructed from our results and compared with the properties of pure CeCoIn 5 under pressure. Effects of chemical pressure and/or hybridization tuning associated with Sn-doping are discussed.

The system CeCoGe3−xSix is of special interest since there is evidence that a quantum critical point of the antiferromagnetic phase can be approached by alloying as well as by application of high pressure. With new results of AC-susceptibility and specific heat measurements on CeCoGe2.1Si0.9 under high pressure presented here, we show by comparison with former data that the tuning parameters composition and pressure, respectively, are equivalent. Alloy and pressure data fit in a common phase diagram. The quantitative behavior of c/T under pressure, too, corresponds to that under changes of composition.

The effect of hydrostatic pressure on the resistivity of Ce(Ru 1− x Fe x ) 2 Ge 2 was studied. Chemical pressure (alloying) and hydrostatic pressure produce similar changes in the physical properties of the series driving it from the ferromagnetic (CeRu 2 Ge 2 ) to the heavy fermion (CeFe 2 Ge 2 ) ground state with (decreasing) unit cell volume as a unique parameter; f-p(CeGe) hybridization is, probably, also giving some contribution to the changes.

We have performed measurements of electrical resistivity, AC susceptibility, magnetization, Mossbauer effect and NMR on the series of intermetallic compounds Ce(Ru 1− x M x ) 2 Ge 2 , M  Fe, Au for 0 ⩽ x ⩽ 0.1. The parent compound CeRu 2 Ge 2 orders ferromagnetically below 7.5 K, with f-electrons showing only a small mass-enhancement at low temperatures. However, its crystal structure and Fermi surface are closely related to the heavy-electron superconductor CeRu 2 Si 2 . Analysis of X-ray diffraction patterns confirmed the structure to be of thCr 2 Si 2 -type, with no foreign phases detected. The results of our Mossbauer studies indicate that Fe goes into the Ru sites with no magnetic moment. NMR signals were observed in the Fe-doped samples with quadrupolar interaction that can be related to 73 Ge nucleus ( I = 9/2).

The intermetallic compound CeCo(Ge1−xSix)3 for x=0, is an antiferromagnetic Kondo lattice system with a double magnetic transition at Tc=21.2 K and TN=19 K. Upon doping with Si, these transitions merge into a single antiferromagnetic transition, as for the x=0.75 composition studied here (TN=5.5 K). We have applied hydrostatic pressure to this material and observed the vanishing of the antiferromagnetic transition as pressure increases, using electrical resistance and AC susceptibility measurements. For T⪡TN, we show that the resistance is dominated by electron–magnon scattering. The magnon spectrum is characteristic of anisotropic antiferromagnets. The gap and stiffness of the spin waves, obtained from the fits of the resistance curves, vary with pressure. We discuss the behavior of these quantities close to the quantum critical point.

We present the results of magnetoresistance ρ(H, T) measurements for CeFeGe3 and CeCoGe3 as a function of temperature in fixed applied fields and as a function of field at fixed temperatures. For CeCoGe3 the H–T phase diagram was constructed from ρ(H, T) results. Temperature dependent magnetoresistance of CeCoGe3 in applied field was fitted taking into account electron–magnon scattering in different regions of the H–T diagram.

Ludwigites are low-dimensional magnetic systems with chemical formula 2MO·M′BO3. For the ludwigites in which M′=Fe and M=Mg, Fe, Ni and Cu we report the following behavior: (1) The ordering temperatures of the Fe3+ sub-system in each compound is higher than that of the respective M sub-system; (2) In particular, the 2FeO·FeBO3 ludwigite presents a reentrant weak ferromagnetism in the range 40–70 K and the coexistence of paramagnetic and antiferromagnetic spins between 70 and 112 K