arXiv subjects

Cinthia Piamonteze

Publications and source records attributed to Cinthia Piamonteze.

24 records · Page 2Linked to original sources

arXiv2015

Evidence for Coexistence of Bulk Superconductivity and Itinerant Antiferromagnetism in the Heavy Fermion System CeCo(In$_{1-x}$Cd$_x$)$_5$

In the generic phase diagram of heavy fermion systems, tuning an external parameter such as hydrostatic or chemical pressure modifies the superconducting transition temperature. The superconducting phase forms a dome in the temperature-tuning parameter phase diagram, which is associated with a maximum of the superconducting pairing interaction. Proximity to antiferromagnetism suggests a relation between the disappearance of antiferromagnetic order and superconductivity. We combine muon spin rotation, neutron scattering, and x-ray absorption spectroscopy techniques to gain access to the magnetic and electronic structure of CeCo(In$_{1-x}$Cd$_x$)$_5$ at different time scales. Different magnetic structures are obtained that indicate a magnetic order of itinerant character, coexisting with bulk superconductivity. The suppression of the antiferromagnetic order appears to be driven by a modification of the bandwidth/carrier concentration, implying that the electronic structure and consequently the interplay of superconductivity and magnetism is strongly affected by hydrostatic and chemical pressure.

cond-mat.supr-con↗

arXiv2015

Surface aligned magnetic moments and hysteresis of an endohedral single-molecule magnet on a metal

The interaction between the endohedral unit in the single-molecule magnet Dy$_2$ScN@C$_{80}$ and a rhodium (111) substrate leads to alignment of the Dy 4$f$ orbitals. The resulting orientation of the Dy$_2$ScN plane parallel to the surface is inferred from comparison of the angular anisotropy of x-ray absorption spectra and multiplet calculations in the corresponding ligand field. The x-ray magnetic circular dichroism (XMCD) is also angle dependent and signals strong magnetocrystalline anisotropy. This directly relates geometric and magnetic structure. Element specific magnetization curves from different coverages exhibit hysteresis at a sample temperature of $\sim4$ K. From the measured hysteresis curves we estimate the zero field remanence life-time during x-ray exposure of a sub-monolayer to be about 30 seconds.

cond-mat.mtrl-sci↗

arXiv2013

Tunneling, Remanence, and Frustration in Dysprosium based Endohedral Single Molecule Magnets

A single molecule magnet (SMM) can maintain its magnetization direction over a long period of time [1,2]. It consists in a low number of atoms that facilitates the understanding and control of the ground state, which is essential in future applications such as high-density information storage or quantum computers [3,4]. Endohedral fullerenes realize robust, nanometer sized, and chemically protected magnetic clusters that are not found as free species in nature. Here we demonstrate how adding one, two, or three dysprosium atoms to the carbon cage results in three distinct magnetic ground states. The significantly different hysteresis curves demonstrate the decisive influence of the number of magnetic moments and their interactions. At zero field the comparison relates tunneling of the magnetization, with remanence, and frustration. The ground state of the tridysprosium species turns out to be one of the simplest realizations of a frustrated, ferromagnetically coupled magnetic system.

cond-mat.mtrl-sci↗

arXiv2011

An electron hole doping and soft x-ray spectroscopy study on La1-xSrxFe0.75Ni0.25O3-δ

The conductivity of the electron hole and polaron conductor La1-xSrxFe0.75Ni0.25O3-δ, a potential cathode material for intermediate temperature solid oxide fuel cells, was studied for 0 <x < 1 and for temperatures 300 K <T < 1250 K. In LaSrFe-oxide, an ABO3 type perovskite, A-site substitu-tion of the trivalent La3+ by the divalent Sr2+ causes oxidation of Fe3+ towards Fe4+, which forms conducting electron holes. Here we have in addition a B-site substitution by Ni. The compound for x = 0.5 is identified as the one with the highest conductivity (σ ~ 678 S/cm) and lowest activation energy for polaron conductivity (Ep = 39 meV). The evolution of the electronic structure was monitored by soft x-ray Fe and oxygen K-edge spectroscopy. Homogeneous trend for the oxida-tion state of the Fe was observed. The variation of the ambient temperature conductivity and activation energy with relative Sr content (x) shows a correlation with the ratio of (eg/eg+t2g) in Fe L3 edge up to x=0.5. The hole doping process is reflected by an almost linear trend by the variation of the pre-peaks of the oxygen K-edge soft x-ray absorption spectra.

cond-mat.str-el↗

arXiv2011

Entanglement of charge transfer, hole doping, exchange interaction and octahedron tilting angle and their influence on the conductivity of La1-xSrxFe0.75Ni0.25O3-δ: A combination of x-ray spectroscopy and diffraction

Substitution of La by Sr in the 25% Ni doped charge transfer insulator LaFeO3 creates structural changes that inflect the electrical conductivity caused by small polaron hopping via exchange interactions and charge transfer. The substitution forms electron holes and a structural crossover from orthorhombic to rhombohedral symmetry, and then to cubic symmetry. The structural crossover is accompanied by a crossover from Fe3+-O2--Fe3+ superexchange interaction to Fe3+-O2--Fe4+ double exchange interaction, as evidenced by a considerable increase of conductivity. These interactions and charge transfer mechanism depend on superexchange angle, which approaches 180° upon increasing Sr concentration, leading an increased overlap between the O (2p) and Fe/Ni (3d) orbitals.

cond-mat.str-el↗

arXiv2003

Phonon Activity and a Possible Lattice Arrangement in the Intermediate Phase of YVO3

We show that in YVO3 new hard phonons gradually become zone center active below ~210 K verifying that a lattice phase transition takes place at about that temperature. The Debye-Waller factor found from EXAFS measurements show an additional disorder below 150K seen as a departure from the thermal behavior. We bring up the similarities of the intermediate phase to known results belonging to incommensurate systems that here we attribute to faulty orbital stacking with possible domain formation set below 116K, the onset temperature of the G-type antiferromagnetism. We found support for this interpretation in the inverted lambda shapes in the measured heat capacity at the phase transitions and in the overall temperature dependence of the reported new hard phonons as compared with those for known incommensurate dielectrics.

cond-mat.mtrl-sci↗