Direct evidence for the suppression of charge stripes in epitaxialLa1.67Sr0.33NiO4films

Abstract

We have successfully grown epitaxial La1.67Sr0.33NiO4 films with a small crystalline mosaic using pulsed laser deposition. With synchrotron radiation, the x-ray diffraction peaks associated with charge stripes have been successfully observed for relatively thick films. Anomalies due to the charge-ordering transition have been examined using four-point probe resistivity measurements. Xray scattering provides direct evidence for suppression of the stripe phase in thin samples; the phase disappears for film thicknesses 2600Å. The suppression appears to be a result of shrinking the stripe phase domains. This may reflect the stripe phase progressing from nematic to isotropic. PACS numbers:The real space ordering of charges, spins, and electronic orbitals in correlated electron materials has been a major topic in condensed matter physics in recent years. Such behavior has been found in a variety of transition metal oxides that exhibit a range of physical properties. A typical situation occurs when antiferromagnetic insulators of these oxides are electronically doped, the charge carriers tend to localize and order [1,2]. One of the most important types of order is generally known as stripes. This is best known in doped compounds of the La 2 CuO 4 family of high temperature superconductors. At a particular density of doped holes, n h = 1/8, there is a static, ordered arrangement of spins and charges forming stripes along the Cu-O bond direction [3]. The isostructural system La 2−x Sr x NiO 4+y shows a similar stripe structure but with an orientation rotated by 45 • with respect to the Ni-O bond direction in the planes. However, it does not exhibit superconductivity and even remains insulating for a wide doping range [4]. Furthermore, a variety of manganese oxide materials appears to show various types of charge, spin, and orbital ordering, some of which are stripe-like [5,6]. More recently, a short-range charge ordering in Ho-doped SrCoO 3−x cobaltite with chargeordered clusters size down to 50Å is observed for a broad compositional range [7]. As more examples of charge inhomogeneity are discovered, one might think that the spin-charge ordering may be a ubiquitous property of transitional metal oxides. However, there are certainly many examples of charge-doped transition metal oxides where no such charge inhomogeneity has been reported. It is thus important to understand the nature of charge ordering correlations, their effect on physical properties, and under what situations they will occur. To further such a goal, it would be very helpful to find a single materials system where the charge orders through an external tuning parameter that does not affect the charge concentration itself.There have been several efforts to investigate the correlation between the stripe phase and lattice distortion by applying mechanical strain in cuprate materials. The static stripe phase in La 1.875 Ba 0.125 CuO 4 and (LaNd) 1.875 Sr 0.125 CuO 4 is accompanied by a structural phase transition from a low temperature orthorhombic (LTO) to a...

Charge order and antiferromagnetism in epitaxial ultrathin films ofEuNiO3

“…These devices typically require ultra thin films or nanoparticles of materials making the study of size effects of paramount importance to future functionality. For instance, it was found that the bulk CO transition is rapidly suppressed in the nano-limit or under high pressure for CMR manganite systems 12,13 ; while in thin films the CO transition temperature can be suppressed entirely or even increased from the bulk value [14][15][16] . Further, to be technologically viable a device typically needs to operate at room temperature and above, while in complex oxides CO is typically a low temperature phenomenon.…”