Possible scale invariant linear magnetoresistance in pyrochlore iridates Bi2Ir2O7

We report the observation of a linear magnetoresistance in single crystals and epitaxial thin films of the pyrochlore iridate Bi2Ir2O7. The linear magnetoresistance is positive and isotropic at low temperatures, without any sign of saturation up to 35 T. As temperature increases, the linear field dependence gradually evolves to a quadratic field dependence. The temperature and field dependence of magnetoresistance of Bi2Ir2O7 bears strikingly resemblance to the scale invariant magnetoresistance observed in the strange metal phase in high Tc cuprates. However, the residual resistivity of Bi2Ir2O7 is more than two orders of magnitude higher than the curpates. Our results suggest that the correlation between linear magnetoresistance and quantum fluctuations may exist beyond high temperature superconductors

Low-temperature processing of ZrB2-ZrC composites by reactive hot pressing

Dense ZrB2-ZrC and ZrB2-ZrCx0.67 composites have been produced by reactive hot pressing13; (RHP) of stoichiometric and nonstoichiometric mixtures of Zr and B4C powders at 40 MPa and13; temperatures up to 1600 C for 30 minutes. The role of Ni addition on reaction kinetics and13; densification of the composites has been studied. Composites of 97 pct relative density (RD)13; have been produced with the stoichiometric mixture at 1600 C, while the composite with13; 99 pct RD has been obtained with excess Zr at 1200 C, suggesting the formation of carbon13; deficient ZrCx that significantly aids densification by plastic flow and vacancy diffusion mechanism.13; Stoichiometric and nonstoichiometric composites have a hardness of 20 GPa. The grain13; sizes of ZrB2 and ZrCx0.67 are 0.6 and 0.4 lm, respectively, which are finer than those13; reported in the literature

Indentation of a hard film on a compliant substrate: film fracture mechanisms to accommodate substrate plasticity

In this paper we discuss various contact damage modes in thin TiN films on steel substrate with increasing load. To understand the displacement at different points along the depth of the film, we have used a TiN–AlTiN multilayered film in which each layer acts as a strain marker and we have also calculated the stresses theoretically using an elastic model of spherical indentation of a bi-layer. The study has helped to understand the physics behind different fracture phenomena, such as confinement of columnar sliding to the middle of the film, the genesis of lateral cracks during unloading, etc. We also emphasize the co-existence and competition of different modes of fracture in the film, rather than a single mode, at a particular combination of film thickness, substrate hardness and load and describe the way different modes interact in the spatial domains when they do coexist

Toughening through multilayering in TiN–AlTiN films

The damage response of columnar multilayers of TiN and AlTiN to Vickers indentation is studied through focused ion beam machining and elastic modelling. Multilayers display an enhanced resistance, which increases with layer refinement, to the multiple fracture modes that appear at high loads in these materials, including edge (nested)cracks and inclined shear cracks. Measurements of layer thickness reveal that multilayers display additional modes of plastic deformation that lead to permanent compression and bending of the film. An elastic model of contact deformation in a bilayer where plasticity is mimicked by greatly enhanced elastic compliance of the film is used to rationalize the trends in crack resistance. It is shown that the enhanced toughness is not due to any increase in the strain capacity (hardness/modulus) of the film material, brought about by multilayering

Effect of residual stress on the fracture strength of columnar TiN films

The intercolumnar fracture strength of a columnar TiN film was deconvoluted by nanoindentation load-displacement curves. The columnar boundary strength of such films strongly depends on the amount of residual stress present in the film. The residual stress of the coating was modified by plastically stretching the substrate. Indentation studies on the columnar TiN coating as a function of residual stress reveals that the column sliding stress diminishes with residual stress, suggesting that the presence of a high compressive stress substantially improves the fracture strength of a columnar TiN film. True film hardness on the other hand does not change

Processing, microstructure and hardness of TiN/(Ti, Al)N multilayer coatings

Multilayer films of TiN/(Ti,Al)N were deposited on stainless steel substrates by rotating the sample continuously between TiN and (Ti, Al)N targets in a cathodic arc evaporation chamber. A complex set of microstructures has been found in which alternate layers of TiN and (Ti, Al)N are separated, at the interface, by another layered interfacial region which consists of extremely fine (4 mn) sub-layers, which result from the secondary planetary rotation of the specimen in the deposition chamber and which is thought to arise from a varying Ti/Al vapour concentration in the chamber. The hardness values of the multilayers show little influence of layer periodicity and no change from those of monolithic TiN and AlTiN films. This absence of strengthening from layer refinement is discussed with respect to the gradient of composition change at the interface and prevailing models of hardening in coherent multilayered systems

Possible scale invariant linear magnetoresistance in pyrochlore iridates Bi2Ir2O7

We report the observation of a linear magnetoresistance in single crystals and epitaxial thin films of the pyrochlore iridate Bi2Ir2O7. The linear magnetoresistance is positive and isotropic at low temperatures, without any sign of saturation up to 35 T. As temperature increases, the linear field dependence gradually evolves to a quadratic field dependence. The temperature and field dependence of magnetoresistance of Bi2Ir2O7 bears strikingly resemblance to the scale invariant magnetoresistance observed in the strange metal phase in high Tc cuprates. However, the residual resistivity of Bi2Ir2O7 is more than two orders of magnitude higher than the curpates. Our results suggest that the correlation between linear magnetoresistance and quantum fluctuations may exist beyond high temperature superconductors