GROWTH AND OPTIMIZATION OF THIN FILMS BASED ON IRIDIUM OXIDE FOR SPINTRONICS

La búsqueda de materiales con un fuerte acoplamiento espín–órbita (SOC) representa una vía muy prometedora a la hora de desarrollar nuevos dispositivos espintrónicos. Dentro de este grupo, el interés en el óxido de iridio (IrO2) ha aumentado notablemente en los últimos años. Esto se debe, entre otros factores, a su estado fundamental, delicadamente equilibrado como consecuencia de diferentes interacciones que compiten en la misma escala energética: SOC, campo cristalino, o repulsiones de Coulomb; lo que ha llevado a recientes estudios teóricos a concluir que el carácter metálico y no magnético del IrO2 puede ser modificado mediante cambios estructurales. De esta manera, motivados por su enorme potencial en espintrónica y por las predicciones que sugieren unas propiedades de transporte eléctrico y magnéticas modificables, esta tesis se centra en el estudio del IrO2. En particular, la investigación llevada a cabo tiene como objetivo principal encontrar evidencia experimental de las transiciones metal–aislante y no magnético–magnético predichas en sistemas basados en IrO2. Para ello, se estudiaron 3 vías alternativas: (1) crecimiento de láminas delgadas de IrO2 con relevantes diferencias estructurales en cuanto a espesor, cristalinidad y parámetros de red se refiere; (2) aplicar presión química mediante dopaje sustitucional; (3) y combinarlo con elementos 3d magnéticos.<br /

Microstructure and indentation hardness study of CAE-PVD (Cr,Ti,Al)N solid solution coatings deposited using a combinatorial multitarget approach

In this study we have analysed the indentation hardness and modulus of cathodic arc deposited CrTiAlN coatings as a function of the stoichiometric variables Ti/Cr, Al content and cation mix. The coatings have been prepared using a combinatorial cathode composition approach, leading up to 14 different stoichiometries produced in 5 batches. The coatings have been inspected by glow discharge optical emission spectroscopy, scanning electron microscopy, X-ray diffraction and nanoindentation techniques. The coatings develop crystalline structures compatible with solid solutions of face-centered cubic unit cells for all the compositions produced. Such unit cells exhibited a downwards lattice parameter dependency on the aluminum concentration of the coatings (from 0.417 nm down to 0.413 nm). The indentation hardness as a function of the Ti/Cr is compatible with other previous studies reported. The films hardnesses and moduli also increase as the aluminum concentration increases (21 GPa up to 34 GPa). Both indentation responses upon Ti/Cr and Al are attributed to solid solution strengthening. However in order to prove this statement, the indentation hardness and modulus were studied as a function of the mixing term of the cations, as this term is well representative of the solid solution compositional map. The observed results unambiguously evidence that the solid solution strengthening effect is confirmed on the basis of the dependency between the indentation hardness and the so called degree of mixing.This work has been funded by the Spanish Ministry of Science and Innovation of Spain through the project PGC2018-096855-A-C44. The authors also acknowledge the Centro para el Desarrollo Tecnológico e Industrial (CDTI) for the support of the excellence program CERVERA through the project CER2019-1003

Probing the tunability of magnetism with external pressure in metastable Sr2NiIrO6 double perovskite

In Sr2NiIrO6 long-range Ir-Ir antiferromagnetic exchange interactions have been reported to overcome the ferromagnetic Ni-Ir interactions hampering the otherwise expected ferromagnetic behavior. Prompted by this, a combination of x-ray absorption spectroscopy and x-ray diffraction at high pressure is used here to investigate the interplay between the magnetic structure of the Ir sublattice and lattice degrees of freedom. The compression of Sr2NiIrO6 drives an unexpected nonmonotonic change of the x-ray magnetic circular dichroism (XMCD) spectra: The intensity first decreases in the 0- to 18-GPa range, then shows an increase in the 18- to 30-GPa range and again decreases for higher pressures. The XMCD intensity, a measure of the net magnetization in the Ir sublattice, however, is found to remain very low in the whole pressure range so the observed changes do not correspond with a transition from antiferromagnetic to ferromagnetic or ferrimagnetic order. The evolution of the XMCD is better explained in terms of a weakening/strengthening of the long-range antiferromagnetic (AFM) Ir-Ir interaction between ferromagnetic planes associated with the reduction of the lattice parameters. In particular, a correlation can be established between the evolution of the b/a ratio and the weakening/strengthening of the AFM interaction.This work was supported by Spanish MINECO Projects No. MAT2014-54425-R (AEI/FEDER, UE), No. MAT201783468-R (AEI/FEDER, UE), and No. MAT2017-84496R (AEI/FEDER, UE), MICINN Project No. PID2020115159GB-I00/AEI/10.13039/501100011033, and the regional Government of Aragon (Grant No. E12-20R RASMIA). E.A.-E. acknowledges the Spanish MINECO and the European Social Fund for a FPI (Formación de Personal Investigador, 2015) grant. This research used resources of the APS, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DEAC02-06CH11357.Peer reviewe

Data for Dimensionality-driven metal-insulator transition in spin-orbit-coupled IrO2

All the experiments have been carried out on thin films of IrO2, the thickness and crystallinity of the each film being specified in each file. X-ray reflectivity (XRR) and X-ray diffraction measurements (XRD) were performed by using Bruker D8 and Rigaku D/max-2500 diffractometers, respectively, by using the Ka radiation line of copper. The electrical resistivity was measured using the four points van der Pauw method by means of a Quantum Design PPMS-9T with no applied magnetic field and with a small electric current (0.1 mA). Magnetization measurements were carried out by using a commercial SQUID magnetometer from Quantum Design. Magnetization versus temperature data were collected from 5 to 350 K with a heating rate of 5 K/min at 1000 Oe. High-energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XANES) measurements were carried out at RT by using a beamline I20-Scanning at Diamond Light Source. More informacion can be found in https://doi.org/10.1107/S1600577518008974. X-ray magnetic circular dichroism (XMCD) measurements were carried out at beamline 4-ID-D of the Advanced Photon Source, Argonne National Laboratory. Measurements were done in a cryomagnet with the sample cooled with 4He vapor. A 500 micron thick diamond phase plate was used to generate circularly polarized X-rays and XMCD measurements were carried out in helicity-switching mode. Measurements were done in fluorescence mode using a grazing incidence geometry and an energy dispersive 4-element Si drift diode detector placed at 90 degrees relative to the incident beam direction. XMCD Data were collected at 10 K with the magnetic fields along and opposite the X-ray propagation direction to remove any artifacts of nonmagnetic origin.Spanish MINECO projects MAT2014-54425-R (MINECO/FEDER, UE), MAT2017-82970-C2-R (AEI/FEDER, UE), MAT2017-83468-R (AEI/FEDER,UE), MAT2017-87134-C02-01-R (AEI/FEDER, UE) and MAT2017-87134-C02-02-R (AEI/FEDER, UE); Spanish MICINN project PID2020-115159GB-I00 / AEI / 10.13039/501100011033; Aragon Regional Government (Projects No. E12-20R and E28-20R); European Union’s Horizon 2020 program Marie Sklodowska-Curie grant agreement no. 665919; European Union’s Horizon 2020 Programme project Quantox of QuantERA ERA-NET Cofund of Quantum Technologies (Grant Agreement No. 731473).XRD_IrO2_001epitaxy.dat XRD_IrO2_100epitaxy.dat XRD_IrO2_110epitaxy.dat XRD_IrO2_110textured.dat AFM_2d2nm_thick_001epitaxy.tif STEM_5d7_nm_thick_001epitaxy.tif XAS_IrO2_001epitaxy_5d7nm.dat XAS_IrO2_001epitaxy_96nm.dat XAS_IrO2_100epitaxy_1d7nm.dat XAS_IrO2_100epitaxy_5d1nm.dat XAS_IrO2_100epitaxy_89nm.dat XAS_IrO2_110epitaxy_5d3nm.dat XAS_IrO2_110epitaxy_92d2nm.dat XAS_IrO2_polycrystalline_films resistivity_IrO2_ 001epitaxy.dat resistivity_IrO2_ 100epitaxy.dat resistivity_IrO2_ 110epitaxy.dat resistivity_IrO2_ 110texture.dat MvsT_IrO2_001epitaxy_1d5nmthick.dat MvsT_IrO2_100epitaxy_1d5nmthick.dat XAS_XMCD_IrO2_100epitaxy_1d5nmthick.dat XAS_XMCD_powderIrO2.dat XRR_IrO2_5nmthick.dat XRR_IrO2_100nmthick.dat XAS_polycrystalline_vs_amorphous.dat rockingcurves_IrO2.dat RSM_IrO2_001epitaxy_5d7nm.dat RSM_IrO2_001epitaxy_96nm.dat RSM_IrO2_100epitaxy_5d1nm.dat RSM_IrO2_100epitaxy_89nm.datPeer reviewe