arXiv subjects

J. Roa-Rojas

Publications and source records attributed to J. Roa-Rojas.

4 recordsLinked to original sources

arXiv2025

Tuning the Topological Properties of the Antiferromagnetic V(Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{4}$ via Sb concentration

The investigation of topological materials has uncovered groundbreaking phases of matter with significant implications for quantum technologies. Here, we explore the antiferromagnetic topological insulator family V(Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{4}$ ($x$=$0$, $0.5$, $1$), formed by introducing vanadium telluride (VTe) layers into the layered topological insulator (Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{3}$. Our results reveal the tunability of the spin Hall conductivity (SHC) and its topological contribution, quantified by the recently introduced average Spin Chern Number (ASCN), via Sb concentration. The materials' strong topological insulating behavior is established through spin-orbit coupling-induced band inversions, nontrivial $\mathbb{Z}_2$ invariants, and the presence of topological surface states. These findings position V(Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{4}$ as promising candidates for next-generation spintronic devices and advanced quantum applications.

cond-mat.mtrl-sci↗

arXiv2019

Bivalent nature of Fe and W ions in the antiferromagnetic Sr2FeWO6 material produced by the combustion technique

The synthesis of the double perovskite Sr2FeWO6 through the direct combustion technique is reported. A complete characterization of the crystalline structure is performed from Synchrotron X-ray measurements and subsequent Rietveld analysis. The results evidence that this material crystallizes in a monoclinic structure, P21/n space group, with strong distortions in the Fe-O6 and W-O6 octahedra, which is consistent with Glazer's notation a-b+a-. A superficial morphological study through scanning electron microscopy images reveals that this synthesis technique allows obtaining nanometric grains with 160 nm mean size. The semiquantitative compositional analysis through spectroscopy of X-ray energy dispersion by electrons shows that the produced material does not contain other chemical elements besides those expected form the stoichiometric formula. Results of analyzes of spectroscopy of photoelectrons emitted by X-rays suggest that there is 66.9% of the material with oxidation states Fe2+ and W6+ and 33.1% with oxidation states Fe3+ and W5+. This bivalence of Fe and W cations is corroborated by means the M\"ossbauer spectroscopy technique. Finally, the magnetic response in AC susceptibility curves allows us to affirm that at low temperatures the material adopts an antiferromagnetic behavior with TN=32 K, with a tendency to the ferromagnetic state above T=150 K mostly due to the presence of Fe3+ ions in the high spin configuration 3d5, S = 5/2.

cond-mat.mtrl-sci↗

arXiv2016

Structure, ferromagnetic, dielectric and electronic features of the LaBiFe2O6 material

In this paper the synthesis and study of the structural, morphological, electrical, magnetic and electronic properties of the LaBiFe2O6 novel material are reported. The material was produced using the standard ceramic method. The Rietveld analysis of experimental data of x-ray diffraction showed that it synthesizes in an orthorhombic perovskite structure (Pnma, #62 space group). Two types of grain, micro and submicrometric, with the LaBiFe2O6 stoichiometry were identified by scanning electron microscopy and X-ray dispersive spectroscopy. Results of electrical polarization and dielectric constant ferroelectric suggest the occurrence of response of the material at room temperature. A T=300 K the material is ferromagnetic and exhibits an anomaly at T=258 K, which is attributed to anisotropy effects, suggesting the occurrence of biferroic behaviour. Results of diffuse reflectance suggest a semiconductor behaviour with energy gap Eg=2,17 eV, which is in agreement with calculations of band structure and density of states for one spin orientation, while for the other spin configuration calculations suggest a conductor feature.

cond-mat.mtrl-sci↗

arXiv2014

Magnetic, electrical and structural properties of the new Re-doped ruthenocuprate Ru1-xRexSr2GdCu2Oy

Despite the discovery of new superconductors classes, high-Tc oxides continue to be a current topic, because of their complex phase diagrams and doping-dependant effects (allowing one to investigate the interaction between orbitals), as well as structural properties such as lattice distortion and charge ordering, among many others. Ruthenocuprates are magnetic superconductors in which the magnetic transition temperature is much higher than the critical superconducting temperature, making them unique compounds. With the aim of investigating the dilution of the magnetic Ru sub-lattice, we proposed the synthesis of the new Ru1-xRexSr2GdCu2Oy ruthenocupratetype family, adapting the known two-step process (double perovskite + CuO)by directly doping the double perovskite, thus obtaining the new perovskite compound Sr2GdRu1-xRexOy, which represents a new synthesis process to the best of our knowledge. Our samples were structurally characterised through X-ray diffraction, and the patterns were analysed via Rietveld refinement. A complete magnetic characterisation as a function of temperature and applied field, as well as transport measurements were carried out. We discuss our results in the light of the two-lattice model for ruthenocuprates, and a relation between RuO2 (magnetic) and CuO2 (superconductor) sublattices can clearly be observed.

cond-mat.supr-con↗