Competing electronic orders in anisotropically strained(Pr0.6Ca0.4)1−<

Abstract

We have explored the competing phases in the anisotropically strained manganese oxide with use of a composition-spread thin film where two contrastive ground states, i.e., ferromagnetic metal and charge/orbitalordered insulator, are designed to compete with a continuous variation in the chemical composition. Taking advantage of a systematic inspection of the phase evolutions, we have confirmed that competing electronic orders could be realized in thin-film form. In particular, we found a possibly one-dimensional orbital-ordered insulating state near the metal-insulator phase boundary which can be disturbed by a relatively low magnetic field.Competing orders and resultant phase instabilities in electronic states of a solid are of great importance for exploiting gigantic or sensitive responses against external stimuli. Realization of such functions has been made with use of thin films and/or junctions with the tuned phase competition and the stable homogeneity in electronic response over tens of nanometer to micron size. Transition-metal oxides with correlated electrons are promising hosts of such functionalities; e.g., insulator-metal or superconducting transition and magnetic transitions induced by electric/magnetic-field stimulation, light irradiation, heat, stress, etc. Compared to bulk materials, however, the phase competition in their thin-film form can be severely suppressed by the epitaxial strain from the substrate. For instance, when transition-metal oxides with simple cubic perovskite symmetry are grown on the ͑001͒ surface of the substrate as shown in Fig. 1͑a͒, biaxial stress usually overwhelms other instabilities and makes the film inactive against additional stimuli. As an effort to minimize such strain effects, the films with a large thickness are grown to make the strain fully relaxed or vicinal substrates are sometimes used to release the accumulated elastic energy at the step edges. 1 The state-of-the-art thin-film technology provides us with another possibility to overcome this problem by exploiting the ͑011͒ orientation of the substrate as shown in Fig. 1͑b͒. 2 In this case, only one axis is directly clamped to the substrate and hence the film gains more freedom so as to behave like a strain-free material. Recently, the charge/ orbital-ordered state for some manganite thin films was realized by this method as in corresponding bulk materials, 2-4 which lowered the barrier in the thin-film technology of correlated-electron system toward its actual application targeting a wider range of bulk properties.Here, we address the issue of phase competition in the thin-film system by investigating the anisotropically strained manganese oxide, ͑Pr 0.6 Ca 0.4 ͒ 1−y ͑La 0.6 Sr 0.4 ͒ y MnO 3 . La 0.6 Sr 0.4 MnO 3 and Pr 0.6 Ca 0.4 MnO 3 are the typical and contrastive systems, where the ferromagnetic metallic and charge/ orbital-ordered insulating ground states are formed, respectively. Furthermore, a size mismatch of constituent ions is comparatively small between La and Sr as well as between Pr and Ca, whic...

Insulator-metal transition driven by change of doping and spin-orbit interaction in Sr2IrO4

“…18 The composition (x) varies continuously along the lateral direction of the substrate over several millimeters. 18,19 Figures 2(c) and 2(d) show intensity distribution of x-ray diffraction related to the lattice constant along the surface normal direction at room temperature, which is obtained from concurrent 2θ /θ x-ray diffraction for the (002) Bragg peak from the substrate and (006) peak from the film. They confirm a continuous variation of the c-axis length with the cation substitutions.…”

“…In particular, our custom designed scanning microscope allows a typical spatial resolution of 100-200 μm for the investigation of composition-spread thin films. 18 The phase change (φ) upon the reflection was determined via Kramers-Kronig transformation as shown in Fig. 3(a).…”

Single-axis-dependent structural and multiferroic properties of orthorhombic RMnO3(R=Gd–Lu)

“…For further fundamental investigations on the relation between lattice and material properties, it is more desirable to prepare samples where only a single lattice parameter is varied with the others fixed for the sake of simplicity. This article discusses the combination of chemical pressure and epitaxy in order to achieve the aforementioned aim as is implicitly applied in Refs [38] and [39]. Here, we utilize only one type of substrate, a (010)-oriented YAlO3 substrate, and coherently grow a series of o-RMnO3 films (R = Gd -Lu) to lock the in-plane lattice parameters.…”