J. García Soldevilla

Transport and magnetic properties of RxR′1−xNi5 (R, R′ = Ce, Pr AND Nd): The effect of comptition between rare earth magnetism

Abstract The crystallography, electrical resistivity, magnetic susceptibility and magnetisation of the CexPr1−xNi5, CexNd1−xNi5 and PrxNd1−xNi5 compounds are presented. The evolution from a magnetic order in NdNi5 to the non magnetic state in PrNi5 (singlet ground level) and CeNi5 (intermediate valence) is discussed. The Curie temperature of NdNi5 decreases proportionally to the amount of substituting Pr or Ce ions. CEF effects on the singlet ground state on the Pr based compounds are detected by resistivity and susceptibility measurements. The influence of the competition between the intermediate valence and the singlet ground state in CexPr1−xNi5 are also analyzed.

Magnetic properties of a new series of Nd-based compounds NdNi1−xCux

Abstract The magnetic properties of the NdNi 1− x Cu x compounds (0.4≤ x ≤ 1) with the FeB-type orthorhombic structure have been studied using electrical resistivity and magnetization measurements. For x ≤ 0.7, the compounds are ferromagnetic ( T C ≈ 35 K) with strong anisotropy, while the compositions with x = 0.9 and 1 are antiferromagnetic, suggesting the existence of complex magnetic structures. This evolution can be understood as a consequence of the modification of the magnetic interactions in large anisotropy compounds.

Magnetoresistivity of the antiferromagnetic Kondo stannide Ce2Ni2Sn

Abstract Ce2Ni2Sn is an antiferromagnetically (TN = 4.7 K) ordered Kondo system. In order to study the crossover from the non-magnetic state to the antiferromagnetic one, we have performed magnetoresistivity measurements on this stannide. Above 6 K, the magnetoresistivity is always negative and decreases when the temperature is lowered (− 20% at 6 K and B = 9 T). This behaviour, observed previously for CeNi2Sn2, can be attributed to the existence of 4f-conduction band hybridization. Below 4 K, a positive magnetoresistance is observed in the low field region, followed by a maximum at a critical field as corresponds to an antiferromagnetic order undertaking a metamagnetic transition.

Annealing and magnetic field effects on the resistivity of Fe-rich FeZr glasses

Abstract Electrical resistivity at zero and applied magnetic fields has been measured in as-quenched and annealed Fe 91 Zr 9 and Fe 90 Zr 10 amorphous alloys between 4 and 320 K. Fe 91 Zr 9 remained amorphous after annealing at 400 K (1 h) while in Fe 90 Zr 10 , traces of crystallites were observed. Similar annealings at 600 K were sufficient to crystallize both alloys, with α-Fe as the main product. A.c. susceptibility shows small changes in the Curie and spin-glass temperatures upon annealing. The resistivity displays a minimum at high temperatures (≅ 250 K), slightly influenced by a magnetic field and thermal treatment. The resistivity is a competition of contributions in which the structure plays the most important role. The presence of magnetic inhomogeneities could also favor an enhanced electronic localization.

Magnetic interactions competing in CeNi1-xCux compounds☆

Abstract We present the crystallographic, electrical and magnetic properties of CeNi 1- x Cu x . An evolution from an enhanced Pauli paramagnetism in CeNi to a Kondo ferromagnet for the intermediate compositions and an antiferromagnetic state for the highest Cu concentrations is found. This behavior is discussed conssidering the changes in volume and density of states which modifies RKKY and Kondo interactions.

Multiphase magnetic analysis through the martensitic transition of TbCu

Abstract We present the neutron diffraction data obtained from both TbCu bulk and powdered samples. This binary alloy undergoes a martensitic transition evolving from a cubic CsCl-type of structure at room temperature to a mixture of cubic and orthorhombic phases at low temperatures. The multiphase Rietveld refinement has been improved due to the specific behaviour of the powdered samples, which do not suffer this transition keeping the same cubic structure along the full temperature range. This combined analysis, which has already been applied with success to GdCu, has allowed us to obtain precise information about the nature of the martensitic transition and the magnetic structure of both the cubic and the orthorhombic phases.

Complex magnetic structures in TbPt1−xCux compounds

Abstract We present neutron diffraction measurements in TbPt 1− x Cu x for x =0, 0.2, 0.4, 0.6 and 0.8 samples. TbPt shows a ferromagnetic non-collinear-C x F z structure. The Cu substitution modifies the conduction band inducing amplitude modulated (AM) structures. For x =0.2 and 0.4, these AM phases coexist with the ferromagnetic ones while for x =0.6 and 0.8 only AM structures are observed.

The role of disorder in the phase diagram of the CeNi1−xCux system

Abstract We discuss the compositional and temperature-phase diagram of the CeNi 1− x Cu x system where non-magnetic, ferromagnetic, antiferromagnetic and spin glass-like states have been found. The substitutional disorder on the Ni/Cu site plays a major role to understand such complex magnetic-phase diagram. A magnetically inhomogeneous spin glass-like state is observed and its stability range depends on the competition between magnetocrystalline anisotropies (at random and coherent) and exchange interactions.

Simultaneous changes of the 4f-conduction band hybridization and the density of states in the CeNi1− xCux compounds

Abstract The interplay between Kondo effect and RKKY interactions is studied in the CeNi 1− x Cu x compounds through the analysis of the evolution of T C or T N (Curie or Neel temperatures) and T K (Kondo Temperature), obtained by means of different methods: susceptibility, resistivity and neutron scattering. With increasing Cu concentration, a ferromagnetic ordering appears for 0.3 ⩽ x 0.8 coexisting with a clear Kondo behaviour while in the Cu rich side the compounds are antiferromagnetic with Kondo interactions decreasing progressively.

Elastic and inelastic neutron scattering on NdNi1−xCux

Abstract The magnetic structures and the crystalline electric field (CEF) excitations of NdNi 1− x Cu x compounds were studied by means of neutron scattering experiments. While a F x C z ferromagnetic ordering is found for x ⩽ 0.7, NdNi 0.2 Cu 0.8 presents a conical arrangement of the magnetic moments, and for x = 0.9 and 1, incommensurate antiferromagnetic structures with several propagation vectors are found. On the other hand, INS spectra show some significant changes in the position of the CEF excitations when Ni is substituted by Cu.